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Dynamic Library Specification
Author: David Dyer-Bennet
MRO1-2/L14
DTN 231-4076
DYER-BENNET AT KL2102, SPAGS::DDB
Edition: 1.0, 18-Jan-84
File: DYN1F.MEM
This document exists online as
KL2137::PS:<DYER-BENNET.PUBLIC>DYN1F.MEM
Dynamic Library Specification Page ii
Issue History 21 May 86
Issue History
Issue 0.1 30-Sep-83 Initial entry. First limited review.
Issue 0.2 14-Oct-83 Signalling details. development.
Issue 1.0 18-Jan-84 Update with things learned from coding and using
the DYNLIB/RTL. Currently in development.
Dynamic Library Specification Page iii
Issue History 21 May 86
1.0 PRODUCT SUMMARY . . . . . . . . . . . . . . . . . . 1
2.0 TERMINOLOGY AND CONVENTIONS . . . . . . . . . . . . 1
3.0 ENVIRONMENT . . . . . . . . . . . . . . . . . . . . 2
3.1 Users . . . . . . . . . . . . . . . . . . . . . . 2
3.2 Hardware . . . . . . . . . . . . . . . . . . . . . 2
3.3 Software . . . . . . . . . . . . . . . . . . . . . 3
3.3.1 Other Software Required For DYNLIB . . . . . . . 3
3.3.2 Other Software That Requires DYNLIB . . . . . . 3
3.4 Services . . . . . . . . . . . . . . . . . . . . . 3
4.0 SOFTWARE CAPABILITIES . . . . . . . . . . . . . . . 3
4.1 Streaming . . . . . . . . . . . . . . . . . . . . 4
4.2 The Run-time Library . . . . . . . . . . . . . . . 4
4.3 Dynamic Invocation Of Libraries . . . . . . . . . 4
4.3.1 Calling A Routine In A Dynamic Library . . . . . 4
4.3.2 Referring To A Galactic Variable . . . . . . . . 5
4.3.3 Errors Occurring During Dynamic Loading . . . . 6
4.4 Memory Allocation . . . . . . . . . . . . . . . . 7
4.5 Signalling And Condition Handling . . . . . . . . 7
4.5.1 Layered Interrupts . . . . . . . . . . . . . . . 8
4.5.2 Condition Handling . . . . . . . . . . . . . . . 8
4.5.2.1 Fixed interrupt channels . . . . . . . . . . 10
4.5.2.2 APR traps . . . . . . . . . . . . . . . . . 10
4.5.2.3 Character interrupts . . . . . . . . . . . . 10
4.5.3 Performance Considerations . . . . . . . . . . 11
4.5.3.1 Arithmetic Trap Default Actions . . . . . . 11
4.6 Errors And Message Printing . . . . . . . . . . 12
4.7 Dynamic Library Contents . . . . . . . . . . . . 12
4.8 Writing Dynamic Libraries . . . . . . . . . . . 13
4.8.1 The Library Definition . . . . . . . . . . . . 13
4.8.2 The LDLBLK File . . . . . . . . . . . . . . . 14
4.8.3 The LDLJCK File . . . . . . . . . . . . . . . 14
4.8.4 Master Initialization . . . . . . . . . . . . 14
4.8.5 Condition Handling Routines . . . . . . . . . 15
4.9 Details Of Data Structures . . . . . . . . . . . 16
4.9.1 The Dynamic Library Block . . . . . . . . . . 16
4.9.2 The Local Dynamic Library Block . . . . . . . 17
4.9.3 The Signal Block . . . . . . . . . . . . . . . 18
4.9.4 The Condition Code . . . . . . . . . . . . . . 19
4.9.5 The Handler Block . . . . . . . . . . . . . . 19
4.10 Details Of Explicit Calls . . . . . . . . . . . 19
4.10.1 Return Last DYNLIB Error -- DY_$LER . . . . . .
20
4.10.2 Force Loading/Overloading -- DY_$LOD . . . . .
20
4.10.2.1 .DYLOD -- Force loading of library . . . . . 21
4.10.2.2 .DYOLB -- overload one library onto another 21
4.10.2.3 .DYOVC -- overload one vector onto another . 22
4.10.3 Global Master Initialization -- DY_$MIN . . . .
22
4.10.4 Allocate Memory Block -- ME_$ALM . . . . . . .
22
4.10.5 Allocate Pages Of Memory -- ME_$ALP . . . . . .
23
4.10.6 Create A New Section -- ME_$ALS . . . . . . . .
Dynamic Library Specification Page iv
Issue History 21 May 86
23
4.10.7 Return Memory Block -- ME_$DLM . . . . . . . .
24
4.10.8 Return Memory Pages -- ME_$DLP . . . . . . . .
24
4.10.9 Destroy A Section -- ME_$DLS . . . . . . . . .
25
4.10.10 Sub-contract Memory Management -- ME_$MEM . . .
25
4.10.11 Formatted ASCII Output -- RL_$FAO . . . . . . .
26
4.10.12 Allocate An Interrupt Channel -- SG_$ALC . . .
27
4.10.13 Disable Interrupt Characters -- SG_$DIC . . . .
27
4.10.14 Return An Interrupt Channel -- SG_$DLC . . . .
27
4.10.15 Deallocate A Signal Chain -- SG_$DLG . . . . .
28
4.10.16 Dump An SG Chain -- SG_$DMG . . . . . . . . . .
28
4.10.17 Enable Interrupt Characters -- SG_$EIC . . . .
28
4.10.18 Establish A Condition Handler -- SG_$EST . . .
29
4.10.19 Establish A Handler Locally -- SG_$LES . . . .
29
4.10.20 Remove A Handler Locally -- SG_$LRM . . . . . .
30
4.10.21 Make Signal Block For Last Monitor Error --
SG_$MER . . . . . . . . . . . . . . . . . . . .
30
4.10.22 Print Error Messages -- SG_$PEM . . . . . . . .
30
4.10.23 Remove A Condition Handler -- SG_$REM . . . . .
31
4.10.24 Declare Trap Handler For Section -- SG_$SEC . .
31
4.10.25 Signal -- SG_$SIG . . . . . . . . . . . . . . .
32
4.11 Details Of Galactic Variables Defined . . . . . 32
4.11.1 Signalling Information . . . . . . . . . . . . 32
4.11.1.1 Enable stack pointer -- SG.ENS . . . . . . . 32
4.11.2 Last-ditch Handler Parameters . . . . . . . . 32
4.11.2.1 Maximum depth -- SG.LEV . . . . . . . . . . 33
4.11.2.2 Destination designator -- SG.OUT . . . . . . 33
4.11.2.3 Prefix table address -- SG.PFX . . . . . . . 33
4.11.2.4 Suffix table address -- SG.SFX . . . . . . . 33
4.11.2.5 Default prefix table -- SG.DPX . . . . . . . 33
4.11.2.6 Default suffix table -- SG.DSX . . . . . . . 33
4.12 DYNLIB Bootstrap . . . . . . . . . . . . . . . . 33
5.0 PUBLICATIONS . . . . . . . . . . . . . . . . . . . 34
6.0 PACKAGING . . . . . . . . . . . . . . . . . . . . 34
7.0 INSTALLABILITY . . . . . . . . . . . . . . . . . . 34
Dynamic Library Specification Page v
Issue History 21 May 86
8.0 EASE OF USE . . . . . . . . . . . . . . . . . . . 34
9.0 PERFORMANCE . . . . . . . . . . . . . . . . . . . 34
10.0 RELIABILITY . . . . . . . . . . . . . . . . . . . 35
11.0 MAINTAINABILITY . . . . . . . . . . . . . . . . . 35
12.0 MAINTENANCE . . . . . . . . . . . . . . . . . . . 35
13.0 COMPATIBILITY . . . . . . . . . . . . . . . . . . 36
13.1 Compatibility With Existing Libraries . . . . . 36
13.2 Product Compatibility . . . . . . . . . . . . . 36
13.2.1 Dependency Issues . . . . . . . . . . . . . . 36
13.3 Standards Conformance . . . . . . . . . . . . . 36
13.4 Internationalization . . . . . . . . . . . . . . 36
14.0 EVOLVABILITY . . . . . . . . . . . . . . . . . . . 36
15.0 COSTS . . . . . . . . . . . . . . . . . . . . . . 36
16.0 TIMELINESS . . . . . . . . . . . . . . . . . . . . 37
17.0 CONSTRAINTS AND TRADES-OFF . . . . . . . . . . . . 37
18.0 APPROVAL PROCESS . . . . . . . . . . . . . . . . . 37
Dynamic Library Specification Page 1
PRODUCT SUMMARY 21 May 86
1.0 PRODUCT SUMMARY
A "routine library" (often called simply a "library" in this document)
is a group of routines and data which is intended to provide services to
its caller. Because the word "library" appears so often in this
document, a routine library is also sometimes called a "package." On
TOPS-20, the most familiar form of library is probably the "REL library"
as understood by LINK and MAKLIB.
A "dynamically linked library" (often called simply a "dynamic library"
in this document) is a library which is merged into a program on request
at execution time.
This document describes a dynamic library system for TOPS-20. This
system provides the following benefits as compared to REL libraries:
o Provide a discipline for independently-developed packages to
share a process peacefully while providing access to the
resources they need to do their jobs (resources that require
discipline to share successfully include address space, the APR
trap system, and the software interrupt system).
o Easier software updates. A new version of a package
implemented as a dynamic library can be introduced into all
programs calling it by simply placing it on the directory from
which dynamic libraries are loaded. There is no need to relink
programs using it.
o More consistent program behavior. If a facility is always
provided by the same package of code, then it will always be
provided in the same way.
o More efficient use of physical memory and swapping space. If a
facility provided by a dynamic library is never called during a
run of a program, that library will never become part of that
process' address space. If several programs are using the same
dynamic library, they will share a single copy of its "pure"
parts.
o Lower cost of engineering other products. Using an existing
package to provide a service is much cheaper than having to
modify it or write one from scratch.
The code to perform dynamic library invocation and related functions
will reside in a special dynamic library called the RTL (run-time
library).
2.0 TERMINOLOGY AND CONVENTIONS
This document specifies the "dynamic library mechanism," which we define
as "that which causes a library to be merged into a program on request,
and performs other functions necessary to make that useful." To avoid
Dynamic Library Specification Page 2
TERMINOLOGY AND CONVENTIONS 21 May 86
confusion, I will from now on call this "DYNLIB." In the rest of this
document, when I refer to a "dynamic library" I am referring generically
or specifically to some library designed to be called through the
services provided by DYNLIB.
DYNLIB has associated with it some special facilities for handling traps
and interrupts, allocating memory, and performing other tasks necessary
to allow many packages to co-exist peacefully in a single process.
These facilities are also specified in this document. They are SIG for
signalling and condition handling (including interrupt and trap
handling), MEM for memory management and section allocation, and RTL for
other utility functions (message formatting and printing, etc.).
Related to DYNLIB are some rules that must be followed by writers of
libraries to be called through DYNLIB. These appear in this document in
a paragraph by themselves, beginning with "DYNLIB use rule:". The full
set of rules for writing a dynamic library will be documented as part of
the development effort of this project.
A "OWL/GBP" is a one-word local/global byte pointer, which is
interpreted as follows: If it has the form of a one-word global
byte-pointer, then it is interpreted as one. If it has the form of a
local byte-pointer, then it is interpreted as pointing into the section
of memory from which it is fetched. This is equivalent to being able to
set an "IFIW" bit in the byte pointer word (which is unfortunately not
supported). The GETBP macro in DYNSYM.UNV performs this operation.
3.0 ENVIRONMENT
3.1 Users
Dynamic libraries will be written primarily by Digital engineers.
Moderately sophisticated customer system programmers may occassionally
be called upon to write dynamic libraries, as may Digital software
specialists.
Dynamic libraries will (eventually) be used implicitly by most
higher-level language programs, but this should be transparent to the
users.
Both application and system programs are likely to invoke dynamic
libraries explicitly.
Digital-written utilities will also use dynamic libraries extensively.
3.2 Hardware
DYNLIB will run on a PDP-10 family processor with extended addressing
(i.e. KL model B). KS processors will not be supported.
Dynamic Library Specification Page 3
ENVIRONMENT 21 May 86
No microcode changes will be required for DYNLIB.
As described below, DYNLIB will encourage the use of extended
addressing. Some dynamic libraries may require fixes for extended
addressing bugs. This will be the responsibility of the project that
produces the dynamic library in question.
3.3 Software
3.3.1 Other Software Required For DYNLIB
DYNLIB requires TOPS-20 release 5.1 or later.
In a future release of the operating system, support for DYNLIB should
be built in. This is discussed under Evolvability. Operating system
support of DYNLIB is not a goal of this project.
3.3.2 Other Software That Requires DYNLIB
DYNLIB is required for Datatrieve-20 V1.0, dynamic extended RMS (V3),
and dynamic callable DBCS (V7) (Dynamic MTHLIB is being produced as part
of the Datatrieve project.)
All other software projects should consider if they would benefit from
using DYNLIB. Language systems should consider invoking their OTS'
through DYNLIB. Languages calling SORT, DBCS, and RMS should consider
calling them through DYNLIB.
3.4 Services
No special services are required for DYNLIB.
4.0 SOFTWARE CAPABILITIES
The basic capability of DYNLIB is to map in an EXE file containing some
package of code at the time a call is made to it. There are some
additional functions associated with this part of DYNLIB, but the bulk
of the routines described in this section are actually support routines
-- they don't directly assist DYNLIB, but they make it possible to write
packages of code that will work together without interference in the
DYNLIB environment.
These support routines are the complicated part of the project. Please
pay close attention to the descriptions of their capabilities and
restrictions.
Dynamic Library Specification Page 4
SOFTWARE CAPABILITIES 21 May 86
4.1 Streaming
"Single-stream" libraries are those like the current SORT which can only
handle one stream of operations at a time, but which have a user
interface such that you make more than one call for that single stream
(some sort of state information is preserved between calls).
"Non-streamed" libraries are those like, perhaps, the MTHLIB, which can
only handle one stream of operations, but where this doesn't matter to
anybody because there is only one call made to perform the operation.
There is no "state" saved across calls to these libraries. Note that to
really qualify in this category a library must be fully reentrant.
"Multi-streamed" libraries are those like callable Datatrieve which
support several concurrent streams of operations. This classification
can be further divided into "infinitely multi-streamed," where it should
always be possible to start another stream, and "limited
multi-streamed," where you could easily run out of streams. Where
"multi-streamed" is used without qualification, "infinitely
multi-streamed" should be assumed.
DYNLIB supports non-streamed and infinitely multi-streamed libraries.
If a caller attempts to initialize a new LDLBLK to a library that has
its busy bit set, a DYNLIB error will be returned. If a library
receives a request to start a stream which it is unable to honor, this
same error should be signalled by the library.
4.2 The Run-time Library
The run-time library (RTL) is a special library that contains the DYNLIB
code and associated facilities (memory management, signalling). This is
an appropriate place to put generally useful routines that aren't big
enough to rate their own library. The MTHLIB has been included in the
RTL, for example.
4.3 Dynamic Invocation Of Libraries
Most calls for DYNLIB services will be made implicitly, by referring to
an address exported from a dynamic library (routine entry point or
"galactic variable").
4.3.1 Calling A Routine In A Dynamic Library
To be able to call routines in a dynamic library, you must:
1. Be running in a non-zero section
2. Have a global-format stack pointer in AC17
Dynamic Library Specification Page 5
SOFTWARE CAPABILITIES 21 May 86
3. Have declared as EXTERNAL in your program the names of the
routines you wish to call
4. Have linked your program with a library-specific REL file for
each of the libraries you call directly (you do not need to
consider libraries that may be called by libraries you call)
5. Have linked your program with DYNBOO.REL
There are two defined types of library-specific REL file that may be
associated with a dynamic library. The normal type is called an "LDLBLK
file"; it contains simply the definition of the LDLBLK. The
alternative type is called an "LDLJCK file"; it contains definitions of
jacket routines for each routine in the library. It may also contain an
ordinary LDLBLK with galactic variable information only.
Suppose the dynamic library EXAMPL contains a routine RNDNAM. The
argument-passing rules for this routine and what registers it preserves
are of no concern to DYNLIB (although they must, of course, be agreed
between the routine and its caller).
To call this routine from MACRO using the LDLBLK file, you must set up
the arguments as specified for the routine, and then
PUSHJ P, @RNDNAM##
This is the normal way of calling a routine in a dynamic library.
To call this routine from MACRO using the LDLJCK file, you must set up
the arguments as specified for the routine, and then
PUSHJ P, RNDNAM##
Note the lack of indirection. When converting an existing program, or a
program written in a higher-level language, to use dynamic libraries,
this mode can be essential. There is no reason for preferring this mode
of call in a newly-written MACRO program, and some performance reasons
for avoiding it.
You may use any number of levels of indirection in the instruction that
calls a routine in a dynamic library. It is also perfectly acceptable
for the PUSHJ instruction to be XCT'd from somewhere else. However, the
EA calc should not depend on the values in the AC's (so don't use
indexing, and don't indirect through an AC).
Normally, the names for the routines in the LDLJCK file and the names
for the transfer vector locations in the LDLBLK file will be the same.
Thus, they cannot both be used in the same program. A technique for
making it possible to use both calling conventions in a single program
is described below.
4.3.2 Referring To A Galactic Variable
To refer to a data location in another library, you must:
Dynamic Library Specification Page 6
SOFTWARE CAPABILITIES 21 May 86
1. Be running in a non-zero section
2. Have declared as EXTERNAL in your program the names of the
galactic variables to which you wish to refer
3. Have linked your program with a library-specific REL file for
the library which defines the galactic variable to which you
wish to refer
To refer to the galactic variable, make an indirect reference through a
"local galactic vector" (like a transfer vector, but the things it
points to aren't routine entry points) which is provided by the
library-specific REL file mentioned above.
The method of referring to a galactic variable is the same whether the
LDLBLK file or the LDLJCK file is used. There is no provision for
referring to galactic variables in languages that do not support the
concept of the indirect reference.
In version 1 of DYNLIB, referring to a galactic variable before the
library which defines it is loaded (either by explicit call to DYNLIB,
or by calling a routine in that library) is an error.
4.3.3 Errors Occurring During Dynamic Loading
There are three ways errors occurring during dynamic loading are
handled, depending on the exact conditions.
If the library being loaded is the RTL, an error message is printed on
the terminal. This is done to minimize the size of the DYNBOO bootstrap
routine. All the code for the fancy error handling described below is
contained in the RTL, which is by hypothesis not available in this
situation.
If the instruction which caused dynamic loading is immediately followed
by an ERJMP or ERCAL instruction, control is transferred to the location
specified. T1 will contain the address of an SG block chain describing
the error. T0 will be trashed. Other registers will be preserved if so
specified for the routine being called.
or can be determined by calling the DYNLER routine, which returns the
signal block for the last error that occurred.
If the instruction which caused dynamic loading is not immediately
followed by an ERJMP or ERCAL instruction, a signal is generated for the
error. This may either be handled by a user error handler, or ignored;
if it is ignored, the last-ditch handler will handle it. For dynamic
library loading errors, its handling is to print a message describing
the error and abort the program.
Dynamic Library Specification Page 7
SOFTWARE CAPABILITIES 21 May 86
4.4 Memory Allocation
The RTL will contain the master section allocator, and a basic memory
manager. All sections must be allocated through the section allocator.
An allocated section is managed by its allocator. One alternative it
has is to manage it itself. Another is to request that the RTL memory
allocator do so for it.
DYNLIB use rule: All sections used must be allocated by the DYNLIB
section allocator.
DYNLIB use rule: Memory in a section may not be used without the
"permission" of the allocator of that section. That is, any sort of
cooperative arrangement is fine, but in the absence of agreement, keep
your fingers in your own sections!
Signal blocks must be allocated by the RTL memory allocator, so that
they can be released by the SIG facility.
A future version of the RTL must support allocation of groups of
contiguous sections. Support for a user-written section allocator is
also desirable (and seems easy).
4.5 Signalling And Condition Handling
To attain the goals of a truly layered product environment, the
facilities of the interrupt system and of trapping must be available to
each package called by a process, without a package having to worry
about which other packages are being used.
DYNLIB use rule: user programs may not directly manipulate the APR trap
system (in particular, they may not use the APR trap function of the
SWTRP% JSYS). User programs should get APR trapping services by using
the JOV or other JFCL-class instruction after the instruction they wish
to check for overflows, or by handling the condition generated in the
absence of JFCL-class instructions.
DYNLIB use rule: user programs should not directly manipulate the
software interrupt (PSI) system except for assigning events to channels
allocated from DYNLIB and handling those interrupts. They should never
perform interrupt-specific JSYSes other than DEBRK%.
There are two asynchronous types of activities that must be supported.
One is asynchronous events requiring attention from the package that
started them. These occur as a normal part of processing, are of
interest only to the package that initiated the activity, and must be
quite quick. This mechanism will be called "layered interrupts".
The other is exception (error) conditions generated by the users' code
and requests. These occur relatively rarely, and quite often result in
an error which is of interest to other packages than the one generating
the condition. The occurrence of these conditions need not be
Dynamic Library Specification Page 8
SOFTWARE CAPABILITIES 21 May 86
blindingly fast. This mechanism will be called "condition handling."
This facility, and the code making it up, is referred to as "SIG"
throughout this document.
4.5.1 Layered Interrupts
This mechanism is intended for servicing of asynchronous events that
belong to a particular package. These are handled by user-specified
interrupt handlers at interrupt level. The user allocates a channel
from SIG, and attaches conditions to the channel himself.
4.5.2 Condition Handling
This mechanism is intended for information of general hierarchical use,
particularly for error or exception information.
This mechanism is modeled after the signalling / condition handling
facilities in BLISS-36, VAX/VMS, and RSX-11.
Conditions may be signalled by user software by making a call to a SIG
routine. In addition to this use, all events made available by TOPS-20
through APR traps or interrupts will be turned into signals by the SIG
facility (APR traps only in V1).
To handle conditions, a routine must identify its handler to SIG.
Conditions that aren't handled by any level will be dealt with by the
"last-ditch" handler.
SIG will maintain a list of handlers established. When a condition is
signalled, the handlers will be called in order from most recently
established to oldest, until one of them handles the situation (see
discussion of handler options below).
There is no facility for a package to grab complete control of some
category of signal; this would violate the hierarchical layering.
Because this facility is based on the existing PSI and SWTRP mechanisms,
there are some restrictions on the user handlers. In particular, some
of them must run at interrupt level. Here are the types of events
signalled, the level at which handlers for them must run, and the
default actions if they are not handled:
Description Level Default Continuable
---------- ----- ------- -----------
APR normal fixup and signal Yes
data error interrupt message and exit Yes
disk quota interrupt message and exit Yes
end of file interrupt message and exit Yes
illegal inst. normal message and exit Restarts instr
illegal read normal message and exit Restarts instr
Dynamic Library Specification Page 9
SOFTWARE CAPABILITIES 21 May 86
illegal write normal message and exit Restarts instr
inferior stop interrupt continue Yes
non-exist. page interrupt create, continue Yes
PDL overflow normal message and exit Yes
software signal normal message & continue Yes
or exit (based on
severity)
system resourc. normal message and exit Yes
character interrupt ^C exits, Yes
others ignored
terminal interrupt ignored Yes
(carrier transition, break, input available)
When a handler is entered for a signal, it has the following options:
re-signal from current position, continue interrupted code, unwind to
its establisher's caller. A handler must also receive the unwind signal
and do appropriate things with it (in particular, it must free dynamic
resources that its establisher allocated). The continue option is only
available for software signals, signals originating as traps, and
signals originating as interrupts that are handled at interrupt level.
There are some restrictions on the linkage conventions of routines which
must enable for condition handling:
o The routines must be running in a non-zero section at the time
they enable, and at any time their handlers are invoked
o There must be a global-format stack pointer in AC17 with
sufficient space available
o The routines must be called with PUSHJ 17, adr.
o The routines must return a value in AC0. It is this value that
may be specified in the unwind call
A routine need not be in a dynamic library to enable for condition
handling. It can be part of a top-level program or a library called in
some other way.
A signal block (or error block) will have a fixed heading, including
facility identification, condition identification, severity
identification, print flags, message text, and pointer to next block.
It will contain a pointer to a block containing condition-specific data.
The normal appearance of a signal is as a chain of these error blocks.
The first one in the chain is the most recent, and for most things is
the only one that needs to be examined. However, for error message
printing, and for more detailed analysis of a situation, the earlier
blocks are available. One of the print flags will indicate that a block
is for computer use only, that no message should be printed.
Dynamic Library Specification Page 10
SOFTWARE CAPABILITIES 21 May 86
4.5.2.1 Fixed interrupt channels
Events that are assigned by TOPS-20 to fixed interrupt channels will be
turned into signals by the SIG facility (not in V1).
Illegal instruction interrupts can result from monitor call errors. The
interrupt will only occur if there is not an ERJMP or ERCAL instruction
after the JSYS that failed. The signal block generated for illegal
instruction interrupts will include as its message the text of the
monitor error message for the JSYS failure.
4.5.2.2 APR traps
APR traps will generate signals unless the instruction producing the
trap is followed by some flavor of JFCL instruction. The default
handling of the signal will be to perform the MTHTRP fixup, print a
message, and then continue.
An alternative method of handling APR traps (and interrupts from fixed
interrupt channels) is discussed under "Performance Considerations",
below.
4.5.2.3 Character interrupts
General handling of character interrupts won't be provided in the first
version. It will probably never be provided. What will be provided is
likely to be good enough for everybody.
There will be two parts to using character interrupts: defining a
character as in interrupt (as opposed to a normal) character, and
processing the signal when it comes by.
Receiving character interrupt signals is the same as receiving any other
signals. There will be a word of signal-specific data giving a mask of
the characters that could have caused this signal (combining interrupt
characters is discussed directly below, and elsewhere in the document;
briefly, it is often sufficient to a program to know that SOME interrupt
character, or some from a small set, was typed, and by assigning more
than one character to a channel when possible the limited set of
channels is conserved).
Characters are defined as interrupt characters by making calls to a SIG
routine giving bit masks. Each call defines a group of characters which
you wish to see treated as interrupt characters. The group of
characters given in a call will not necessarily be distinguishable from
each other when the signal arrives.
If you ask to distinguish between characters that somebody else has
already asked to see combined, you lose (and get a code to that effect).
As a special exception, ^C, ^T, ^A , and ^Y will never be combined with
anything else, although you can request them in combination with other
things. (The exact list of characters given this special treatment is
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certainly open to debate. It has no particular impact on performance or
development time.)
At a future date, the software handling this could be re-written to
optimize assignment of groups of characters to channels so as to allow
you to see any combination you want, subject to the availability of
channels. This is not a requirement of any software we know. This
extension would only be implemented if required by some future software.
Its implementation would be transparent to existing software.
4.5.3 Performance Considerations
There are many packages which get called many times during a relatively
short program run. For example, MTHLIB, RMS (once per record),
sometimes SORT. It is important to minimize the cost of an explicit
layer transition.
Actual exceptions occur relatively rarely, and when they do often result
in program termination or at least user interaction. Accordingly, it is
not as important for the actual handling of exceptions to be fast.
Trading off slower exception handling for faster layer transitions is a
desirable thing to do. (Obviously in an ideal world both would take
zero time. If you know how to achieve this, please come explain it to
me....)
The one possible exception to this is arithmetic traps. These can
sometimes occur without indicating a package-level error, and thus may
occur frequently in a single run. Some packages treat arithmetic traps
as errors. For them, signalling the trap is fine. Some things (written
in MACRO) want to test for errors immediately after the instruction that
produced them. For them, we are making the default handling of a trap
include a check for a JFCL-class instruction right after it. If such an
instruction is present, the trap is ignored.
To ease conversion of existing libraries, and improve performance of
libraries depending extensively on APR traps, there is a facility for
requesting that all traps originating in a given section be directed to
a specified handler. This option, if invoked, completely bypasses
MTHTRP fixups, signal generation, and message printing for APR traps
originating in specified sections.
4.5.3.1 Arithmetic Trap Default Actions
Fixups are as performed by MTHTRP. Putting a JFCL (of any flavor) after
an instruction that may cause an overflow will work normally (MTHTRP
looks for them). In the absence of a JFCL, after determining the error
and possibly fixing things up MTHTRP generates a signal. If this signal
isn't intercepted, the last-ditch handler will print the message it
describes.
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4.6 Errors And Message Printing
The signal block contains information to make printing error messages as
easy as possible -- for example, facility names and error messages are
present as text, so no decoding is necessary. There are also print
flags in the blocks, specifying any special aspects of that block (such
as a block which is for computer use only, contains no message, and
should not be printed at all).
A routine is provided for printing the messages from some initial
segment of the signal blocks in a chain in a uniform format. This is
used by the last-ditch handler, and is recommended for use by user
routines that wish to print messages.
4.7 Dynamic Library Contents
A dynamic library consists of several pieces, including
An EXE file which contains:
o A PDV with the name "DYNLIB$class-name". Word 2 (formerly
called .PVSTR) in the PDV should point to the master dynamic
library block (DLBLK) for this library. Word 4, .PVVER, by
convention contains the version number of the library.
o The DLBLK for the library. This block describes the entry
points and other exported addresses of the library.
o The necessary code and data to perform the library's functions.
A REL file which contains information for the caller to link with.
The normal case (an LDLBLK file):
o The local dynamic library block (LDLBLK) for the library. This
block describes the entry points and other exported addresses
of the library and contains the address vectors through which
references to the actual library objects are made.
A special case, useful when converting callers of existing libraries or
making the calls from higher-level languages that don't support the
concept of pointers to routines (an LDLJCK file):
o The local dynamic library block (LDLBLK) for the library. This
block describes the entry points and other exported addresses
of the library and contains the address vectors through which
references to the actual library objects are made.
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o A jacket routine for each routine in the library. This routine
expects to be called by a simple PUSHJ. It then calls the
routine in the library through the transfer vector.
4.8 Writing Dynamic Libraries
A library is put together from four parts:
1. The code and data to perform the library functions
2. A definition of the library entry points and characteristics
3. A LDLBLK file
4. A LDLJCK file
Parts three and four can (and should) be built automatically from part
one by using the $DLBLK, $LDLBLK, and $LDLJCK macros from DYNSYM.UNV.
Note that making an existing library into a dynamic library can
sometimes be fairly easy, requiring only the production of a library
definition.
4.8.1 The Library Definition
The library definition provides one place to put all the declarations
relating to the dynamic library and its exported addresses. This makes
for easy reference, and fewer mistakes since all places using this
information get it from the definition.
The definition must specify:
o Library name -- must be a valid MACRO name
o Library abreviation -- two characters
o Library macro name -- must be a valid MACRO name
o Library version -- TOPS-20 version number word
o Default version matching rule for this library
o Service class name -- quoted string
o File spec for library EXE file -- quoted string
o List of DIGITAL-specified entry point names in their specified
order. Each entry in this list may be either a single name, or
a sublist as follows:
1. Name for this exported address (routine or galactic
variable)
2. Jacket entry name for routine (defaults to same as address
name)
3. Condition handling flag (defaults to off)
All of the entry points defined by DIGITAL must be present, or
an error will be issued when you compile the definition.
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o List of library-specific entry point names. Same rules as for
previous entry
o List of DIGITAL-specified galactic variable names in their
specified order. All of the galactic variables defined by
DIGITAL must be present, or an error will be issued when you
compile the definition.
o List of library-specific galactic variable names
o Value to statically initialize user word in DLBLK to
o Value to statically initialize user word in LDLBLK to
o Value to statically initialize flag word in DLBLK to
o Value to statically initialize flag word in LDLBLK to
4.8.2 The LDLBLK File
For each library, there must be a source file to build the LDLBLK file.
Its contents should be as follows:
SEARCH DYNSYM, library-sym
$LDLBLK library-macro
END
4.8.3 The LDLJCK File
For each library, there must be a source file to build the LDLJCK file.
Its contents should be as follows:
SEARCH DYNSYM, library-sym
$LDLJCK library-macro [, just-routine-jacket-flag]
END
If the just-routine-jacket-flag is set, the LDLJCK file will contain
only the routine jacket information and will need to be loaded along
with the LDLBLK file. Furthermore, in this case you must have specified
alternate names for all the LDLJCK routine entry points, or else you
will have multiply defined global symbols when you link your program.
(The just-routine-jacket-flag is not supported in V1.)
4.8.4 Master Initialization
The master init routine of a library should, when called, set that
library to a clean state. A freshly master initialized library should
behave exactly as if a clean copy had been loaded.
One of the most important things to do in the master initialization
routine is to properly initialize the memory allocation tables. This
should be done by using a static data structure made at the time the
library was built. Attempting to snoop for free pages in the master
initialization routine won't work, since pages used during a run will
not be free, and yet should become available after master
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SOFTWARE CAPABILITIES 21 May 86
initialization.
The master initialization routine should not do a RESET% JSYS, that will
be done by the top-level program.
The master init routine is called with a PUSHJ 17, adr. It may trash
all registers.
Arguments: None
Return values:
1. Completion status. 0 means OK, anything else means failure. A
master init routine may also signal a condition that indicates
failure.
Error conditions: library-dependent
4.8.5 Condition Handling Routines
A condition handler is called with a PUSHJ 17, adr. It may use all
registers.
Arguments:
1. Address of SIG block for signal to handle.
If the signal is of class SG%UNW, the handler is expected to perform any
necessary cleanup and then exit. No value is returned in this case.
If the signal is of any other class, the handler is expected to decide
what should be done about the condition, and indicate this to SIG by its
return value.
Return values:
1. AC0 is the value to be returned by this handlers establisher
(ONLY IF AC2 CONTAINS .HNUNW)
2. AC1 is the signal block to pass upwards (ONLY IF AC2 CONTAINS
.HNRES)
3. AC2 is the action code describing what action to take:
o .HNUNW -- unwind. This causes a return from the
establisher of this handler to the caller of the
establisher, passing in AC0 the return value specified now
in AC0.
o .HNCON -- continue. This ends condition handling and
causes processing to continue from after or at the
instruction that initiated the signal.
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o .HNRES -- resignal. This passes the same or a modified
condition on to any higher-level condition handlers. In
general, a signal block should not be modified unless you
own it; to resignal a different condition than the one you
received, make a new signal block containing what you want
to say, and set its .SGNXT pointer to the block you
received.
4.9 Details Of Data Structures
4.9.1 The Dynamic Library Block
1. .DYCNT -- block word count (must be 9 currently)
2. .DYFVN -- Block format version number
3. .DYFLG -- Flag word (DIGITAL defined only)
1. DY%BSY -- Busy: library can't start a stream
2. DY%VER -- Version matching rules. Version number from
DLBLK in this library is compared to version number in
LDLBLK and this library is accepted if:
1. DY%MAG -- major version of library greater than major
version of LDLBLK
2. DY%MAL -- major version of library less than major
version of LDLBLK
3. DY%MIG -- major versions equal and minor version of
DLBLK greater
4. DY%MIL -- major versions equal and minor version of
DLBLK less
4. .DYUSR -- Library-use word
5. .DYVER -- Library version number
6. .DYDTV -- IFIW Address of DIGITAL-specified entry-point vector
(DTVEC)
7. .DYCTV -- IFIW Address of library-specific entry-point vector
(CTVEC)
8. .DYDGV -- IFIW Address of DIGITAL-specified galactic variable
vector (DGVEC)
9. .DYCGV -- IFIW Address of library-specific galactic variable
vector (CGVEC)
[The possibility of additional entries is reserved to DIGITAL]
For each of the four classes of exported addresses described above,
there is a separate address vector. Each is a counted vector.
DTVEC: diglen+1
IFIW routine entry-point
. . .
IFIW routine entry-point
CTVEC: cuslen+1
IFIW routine entry-point
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SOFTWARE CAPABILITIES 21 May 86
. . .
IFIW routine entry-point
CGVEC: cgalen+1
IFIW address
. . .
IFIW address
4.9.2 The Local Dynamic Library Block
This block is linked into a calling program from a library-provided REL
file. It provides the section-local indirect words necessary for
referring to addresses in other sections. It also provides the
information to identify and map in the library being called, if
necessary.
1. .LDCNT -- Word count (block length) (must be 11 currently)
2. .LDFVN -- DYNLIB version number for which this LDLBLK was
compiled
3. .LDFLG -- Flag word (DIGITAL-defined only). Flags defined are:
1. LD%VMA -- Use version match rules from this LDLBLK rather
than from DLBLK
2. LD%VER -- Version matching rules. Version number from
DLBLK in library found is compared to version number in
this LDLBLK and that library is accepted if:
1. LD%MAG -- major version of library greater than major
version of LDLBLK
2. LD%MAL -- major version of library less than major
version of LDLBLK
3. LD%MIG -- major versions equal and minor version of
DLBLK greater
4. LD%MIL -- major versions equal and minor version of
DLBLK less
3. LD%INI -- Initialized: library has been loaded and vectors
updated
4. .LDUSR -- User word; may be set by calling program in any way
it wants
5. .LDCLS -- OWL/GBP to "service class" string
6. .LDSPC -- OWL/GBP to file spec string
7. .LDVER -- Library version number
8. .LDDTV -- IFIW Address of DIGITAL-specified entry-point vector
(LDTVEC)
9. .LDCTV -- IFIW Address of library-specific entry-point vector
(LCTVEC)
10. .LDDGV -- IFIW Address of DIGITAL-specified galactic vector
11. .LDCGV -- IFIW Address of library-specific galactic vector
(LCGVEC)
[The possibility of additional entries is reserved to DIGITAL]
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As in the DLBLK, there is a transfer vector for each of the four classes
of exported addresses described above.
4.9.3 The Signal Block
This data structure represents one level of a signal in progress. The
top (most recently added) level of a signal in progress is supplied to
routines. Lower levels are available by following the pointer to next
block.
All of the pointers are expected to point either into the signal block,
or into static storage (which need not be released when the signal block
is released). The pointers may not point into stack storage, as this
may have been released by the time the pointer is used!
Block contents:
1. .SGCC -- Condition code
2. .SGNXT -- xFIW address of next block
3. .SGFAC -- OWL/GBP to ASCIZ facility name
4. .SGCND -- OWL/GBP to ASCIZ condition name
5. .SGMSG -- OWL/GBP to ASCIZ message
6. .SGPC -- PC of source of signal
7. .SGCLS -- Class of condition (bit mask)
o SG%UNW -- Unwind
o SG%APR -- APR trap
o SG%DER -- Data error interrupt
o SG%QUO -- Disk quota interrupt
o SG%EOF -- End of File interrupt
o SG%ILI -- Illegal instruction interrupt (or monitor call
error)
o SG%ILR -- Illegal memory read interrupt
o SG%ILW -- Illegal memory write interrupt
o SG%INS -- Inferior stop interrupt
o SG%NXM -- Non-existent page interrupt
o SG%PDL -- PDL overflow interrupt (not useful?)
o SG%SOF -- Software-originated signal
o SG%RES -- System resources interrupt
o SG%CHR -- Character interrupt
o SG%TRM -- Terminal interrupt
8. .SGFLG -- flag word (DIGITAL-defined only)
o SG%INT -- At interrupt level
o SG%NPR -- Do not print this block (computer use only)
o SG%DYN -- This block is dynamic and may be thrown away
9. .SGDAT -- xFIW address of signal-specific data, such as:
o Character mask for character interrupt
o Values involved for APR traps
o Page number for nonexistent page traps
o Stack pointer for stack overflow traps
o User data for software signals
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4.9.4 The Condition Code
A condition code is a one-word representation of the raw bones of a
condition. It is essentially the same as a BLISS-36 condition code.
SG%FAC SG%MSG SG%SEV
+---+---------------------------+---------------------------+---+
| | | | |
+---+---------------------------+---------------------------+---+
0 0 0 1 1 3 3 3
0 3 4 7 8 2 3 5
Bit 4 (SG%FCD) is set if the facility is customer-defined, clear if
DIGITAL-defined. Bit 18 (SG%MCD) is set if the message is
customer-defined, set if DIGITAL-defined. SG%ID covers the full
condition ID, bits 4-32. SG%SUC is the success bit (35).
4.9.5 The Handler Block
A handler block is the set of information describing an establishing of
a handler. It is the argument passed to the SIGEST routine. This block
may be dynamically allocated, but it must remain in existence (in the
same place) throughout the life of the handler it describes.
1. .HNHND -- xFIW address of handler
2. .HNCLS -- Enable mask (see bit definitions above)
3. .HNCIM -- Character interrupt mask
4. .HNUDA -- xFIW address of user data
5. .HNLEN -- Size of block in words
4.10 Details Of Explicit Calls
There are many functions that the user may request DYNLIB and related
facilities to perform. These functions are implemented in the run-time
library; they are called as any dynamic library routine.
Unless specified otherwise, errors are reported by signalling. This
signal can be prevented by placing an ERJMP or ERCAL instruction
immediately following the potentially offending instruction (and in this
case the address of the signal block is returned in AC1).
The calling sequence for these routines is as follows: Arguments go in
sequential registers starting with AC1. Return values go in registers
sequentially following the arguments, unless specified otherwise (such
as updated values of input arguments). The routines should be called as
ordinary routines in a dynamic library -- with PUSHJ P, @routine-name.
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SOFTWARE CAPABILITIES 21 May 86
Registers 6-17 are preserved unless otherwise specified.
4.10.1 Return Last DYNLIB Error -- DY$LER
(Not in V1)
Returns the address of the signal block (first of chain) describing the
last DYNLIB error, or 0 if no error has been detected. This signal
chain is dynamically allocated; if another DYNLIB error occurs between
the time you get the information and the time you use it, it will be
invalid. You should not attempt to de-allocate this block.
Arguments: None
Return values:
1. Address of signal block (first of chain), or zero if no error
occurred
Error conditions: None
4.10.2 Force Loading/Overloading -- DY$LOD
(Not in V1)
Force the loading of a dynamic library before a reference to an address
exported from it occurs. This could be useful, for example, to cause
the loading of a library containing a galactic variable you need to
reference when there are no routines in that library, or none that you
want to call.
This call also supports overloading -- deliberately loading information
about two libraries into one LDLBLK. This can be useful to replace a
few routines in a library with private copies, without having to
duplicate the entire library. These private copies could be debugging
versions of routines not yet ready to be included in the real library,
for example.
Arguments:
1. Function
1. .DYLOD -- Force loading of library. This function cannot
be applied to the run-time library.
2. .DYOLB -- overload one library onto another
3. .DYOVC -- overload one vector onto another
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SOFTWARE CAPABILITIES 21 May 86
Other arguments depend on the function code.
The normal rules for overloading are as follows:
1. LTVEC entries not containing their default initial state will
not be altered. The default initial state is "IFIW LDLBLK-1"
for the user-mode implementation.
2. If an MTVEC entry contains 0 in its right half, the
corresponding LTVEC entry is not altered. 0 in the right half
covers IFIW 0 and location 0 in any section.
3. If the LTVEC is longer than the MTVEC, excess LTVEC locations
are not altered.
4. If the MTVEC is longer than the LTVEC, the additional MTVEC
entries are ignored.
4.10.2.1 .DYLOD -- Force loading of library
Additional arguments:
1. Address of the LDLBLK of the library to load
Error conditions:
o Any error possible when implicitly loading a dynamic library
4.10.2.2 .DYOLB -- overload one library onto another
Load one library over another according to the rules for overloading.
Standard version checking is performed on both DYNLIB and library
versions for both source and destination libraries.
Arguments:
1. Address of LDLBLK of source library (need not be already mapped
in)
2. Address of LDLBLK of destination library (need not be already
mapped in)
Error conditions:
o Any error possible when implicitly loading a dynamic library
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4.10.2.3 .DYOVC -- overload one vector onto another
This function is used to overload only one address vector from one
library over another. Standard version checking is performed on both
source and destination libraries.
Arguments:
1. Address of LDLBLK of source library
2. Address of source vector
3. Address of LDLBLK of destination library
4. Address of destination vector
Error conditions:
o Any error possible when implicitly loading a dynamic library
may occur
4.10.3 Global Master Initialization -- DY$MIN
Resets all libraries already mapped in to their uninitialized state by
calling the master initialization point in each such library.
All registers are trashed.
Arguments: None
Error conditions:
o Any error condition signalled or returned in the defined manner
by any of the master initialization routines called is passed
on to the caller of DY$MIN.
4.10.4 Allocate Memory Block -- ME$ALM
Allocate a block of memory without page alignment.
Arguments:
1. Chunk identifier
2. Block size in words
Return values:
1. (in T1) Chunk identifier
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2. (in T2) Address of block allocated
Error conditions:
o No room in chunk specified for block requested
o Chunk specified is invalid
The block returned starts at the address given and is the length
specified. The words preceeding and following the block contain RTL
information used when the block is released. Since this word is not
part of the block given you, it should be no strain to keep your hands
off it!
4.10.5 Allocate Pages Of Memory -- ME$ALP
(Not in V1)
Allocate memory in full, contiguous pages.
Arguments:
1. Chunk in which to allocate
2. Number of pages to allocate
Return values:
1. Address of first page allocated
Error conditions:
o Section not under control of RTL
o Space requested not available in section requested
4.10.6 Create A New Section -- ME$ALS
(Not in v1)
Allocates a free section and creates it (the monitor doesn't
automatically create a section when you first refer to an address in it,
as it does for individual pages within pre-existing sections).
Optionally, puts the newly-created section under the control of the RTL
memory manager.
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This is the only valid way to create a section in the DYNLIB
environment. (The section that a new dynamic library is mapped into is
allocated through ME$ALS by DYNLIB.)
This should probably be extended to allocate groups of contiguous
sections.
Arguments:
1. Set if section should be controlled by the RTL memory manager
Return values:
1. Number of the section allocated
Error conditions:
o No sections available
4.10.7 Return Memory Block -- ME$DLM
Return a block of memory allocated with ME$ALM.
Arguments:
1. Address of block to return
Return values: None
Error conditions:
o ME$NAL: Block wasn't allocated
4.10.8 Return Memory Pages -- ME$DLP
(Not in V1)
Arguments:
1. Address of first page
2. Number of pages
Return values: None
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SOFTWARE CAPABILITIES 21 May 86
Error conditions:
o Section not under control of RTL
o Some or all of the pages being returned were not allocated
4.10.9 Destroy A Section -- ME$DLS
(Not in V1)
Sections not under the control of the RTL memory manager are destroyed
immediately on request.
Sections controlled by the RTL memory manager are "frozen" on this call
-- no more space will be allocated out of them. They will be destroyed
when all of the space allocated from them is returned.
This needs support for groups of sections (as in ME$ALS).
Arguments:
1. Section number
Return values: None
Error conditions:
o Section is not allocated
4.10.10 Sub-contract Memory Management -- ME$MEM
Create a memory chunk that can be allocated from.
Arguments:
1. Address of first word of chunk
2. Address of last word of chunk
Return values:
1. Chunk ID in T3
Error conditions:
o ME$NCA: No chunk ID available
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4.10.11 Formatted ASCII Output -- RL$FAO
Format a message given a model string and some arguments to fill in
from.
Arguments:
1. Destination string pointer
2. Max allowable destination string length
3. Model (pattern) string pointer
4. Address of first arg (others follow at higher addresses). Note
that this may be on the stack, or elsewhere; FAO doesn't care
5. Count of args
Return values:
1. Destination pointer is updated in T1
2. Count is decremented in T2
3. T3-T5 are trashed
The pattern string is a simple ASCIZ string with special escape
sequences in it that cause substitution from the list of arguments.
Each argument is used at most once, in the order listed.
All escape codes begin with an exclamation point. The codes and their
meanings are:
!/ Put a CRLF into output
!_ Put a TAB into output
!! Put an exclamation mark into output
!^G Put a BEL into output (ASCII 7, not G)
!OW Put next arg to output as octal word
!SW Put next arg to output as signed decimal word
!OH Put next arg to output as octal halfwords (good
for PC's)
!AA Put 7-bit ASCIZ string at address given by next
arg to output
!AZ Put ASCIZ string pointed to by next arg to
output
!AC Put string pointed to by next arg to output, max
of next arg
chars
!%S Put capital S to output if last number printed
was not 1
!%s Put lower case s to output if last number
printed was not 1
!JFN Put file spec corresponding to JFN in next arg
to
output
!VER Put next arg to output interpreted as version
number
!JER Put JSYS error text for error code in next arg
to
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SOFTWARE CAPABILITIES 21 May 86
output
4.10.12 Allocate An Interrupt Channel -- SG$ALC
(Not in V1)
Arguments: None
Return values:
1. Channel assigned
Error conditions:
o No interrupt channels available
4.10.13 Disable Interrupt Characters -- SG$DIC
(Not in V1)
Requests that a character be made a non-interrupt character. Note that
the count of enable versus disable requests is what controls the actual
status of a character at any given moment
Arguments:
1. Character mask
Error conditions: None
4.10.14 Return An Interrupt Channel -- SG$DLC
(Not in V1)
Arguments:
1. Interrupt channel to return
Return values: None
Error conditions:
o The interrupt channel returned was not allocated
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4.10.15 Deallocate A Signal Chain -- SG$DLG
Deallocate all blocks in a signal chain flagged as dynamic.
Arguments:
1. Address of first block in chain
Return value: None
Error conditions:
o ME$NAL: Block not allocated (for any block along the chain)
4.10.16 Dump An SG Chain -- SG$DMG
Print a formatted dump of a chain of SG blocks on the terminal.
Arguments:
1. Address of first block in chain
Return Value: None
Error conditions: None
4.10.17 Enable Interrupt Characters -- SG$EIC
(Not in V1)
Requests that a set of characters be made interrupt characters. The
count of enable versus disable requests is what controls the actual
status of a character at any given moment.
Arguments:
1. Character mask
Return values: None
Error conditions:
o Insufficient interrupt channels available
o Cannot isolate characters you want from previous requests
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4.10.18 Establish A Condition Handler -- SG$EST
Establish a condition handler for the current routine. SIGEST must be
called before anything is done to the stack within the routine.
For non-macro programs, the technique for establishing is to make a
jacket routine that performs this call. This is done automatically when
you set the "jacket" flag in the library definition for this routine.
(Not in V1)
There are restrictions on the linkage conventions of routines that
establish handlers.
ALL registers are preserved.
Arguments (pushed onto the stack before call):
1. Address of handler block (this block may be dynamically
allocated, but it must remain in existence throughout the life
of the handler)
Return values: None
Error conditions:
o Invalid handler block
o Insufficient room on enable stack
4.10.19 Establish A Handler Locally -- SG$LES
This is a version of SG$EST to be called from within BLISS routines.
This routine is for use by WIZARDS only!! In particular, unwinding to a
routine that enables for condition handling this way is almost certainly
a mistake.
Registers 2-16 are preserved.
Arguments:
1. Address of handler block
Return Values: None
Error conditions: None
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SOFTWARE CAPABILITIES 21 May 86
4.10.20 Remove A Handler Locally -- SG$LRM
Remove a locally established handler
Registers 2-17 are preserved.
Arguments:
1. Address of handler block
Return value: None
Error conditions:
o SG$ROS: Cannot remove a handler other than the most recently
established
4.10.21 Make Signal Block For Last Monitor Error -- SG$MER
(Not in V1)
Arguments: None
Return values:
1. Address of signal block created
Error conditions:
o No monitor error has occurred
4.10.22 Print Error Messages -- SG$PEM
Prints a sequence of error messages from a chain of signal blocks.
Various arguments control depth and format of printing.
Arguments:
1. Destination designator
2. Address of signal block
3. Maximum depth to print messages for
4. Address of suffix list
5. Address of prefix list
Dynamic Library Specification Page 31
SOFTWARE CAPABILITIES 21 May 86
The prefix and suffix lists are vectors of OWL/GBP to ASCIZ strings,
intended to be indexed by severity. The strings pointed to are prefixes
and suffixes for messages.
Return values: None
Error conditions:
o Invalid signal block encountered
4.10.23 Remove A Condition Handler -- SG$REM
Remove the condition handler established for the current routine. This
must be done just before routine exit.
All registers are preserved.
Arguments (push on stack):
1. Address of handler block (must be same block passed to SIGEST)
Return values: None
Error conditions:
o The handler being removed is not the most recently established
one
o Invalid handler block
4.10.24 Declare Trap Handler For Section -- SG$SEC
(Not in V1)
Specify an APR trap and fixed interrupt handler for all events occurring
in a specified section. This is provided for convenience in converting
existing libraries with their own trap handlers, and to allow use of
traps in a library without the overhead of enabling for condition
handling.
Arguments:
1. Section number
2. Address of handler block
Return values: None
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SOFTWARE CAPABILITIES 21 May 86
Error conditions:
o A handler has already been established for the section
specified
o The section specified does not exist
4.10.25 Signal -- SG$SIG
Signal a software condition. Under some conditions, this routine does
not return. This is determined by whatever handler finally handles the
signal. If it does return, it returns with all registers preserved.
Arguments:
1. Address of signal block
Return values: None
Error conditions:
o Invalid signal block
4.11 Details Of Galactic Variables Defined
The RTL defines some galactic variables to allow users to control
certain aspects of its operation without having to make calls to special
routines to set internal values.
4.11.1 Signalling Information
SIG makes certain internal information available as galactic variables.
4.11.1.1 Enable stack pointer -- SG.ENS
The stack pointer for the enable stack. Each frame on the enable stack
holds an establish block describing one handler that is currently
established.
This is for use by experts only! You can cause a lot of trouble with
this, if you want.
4.11.2 Last-ditch Handler Parameters
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SOFTWARE CAPABILITIES 21 May 86
4.11.2.1 Maximum depth -- SG.LEV
No more than this many levels of messages will be printed (blocks in a
signal chain for which no message is printed do not count against this
limit). To print "all" levels, set this to an outrageously high
positive value. Signal chains should never get "too" deep.
4.11.2.2 Destination designator -- SG.OUT
Last-ditch messages may be directed to places other than primary output.
If attempting to output to the destination specified fails, it will be
reset to primary output and the message will be printed there. Setting
this to a byte pointer has some potential problems -- it doesn't get
copied back to SG.OUT after it's used, so messages will overlay each
other in the memory area specified.
4.11.2.3 Prefix table address -- SG.PFX
The prefix table is indexed by severity to find the OWL/GBP to an ASCIZ
string to print before the message. This is where the "?" before errors
or the "[" before informational messages comes from.
4.11.2.4 Suffix table address -- SG.SFX
Like SG.PFX, but strings go after the message. This is where the "CRLF"
after errors or the "]CRLF" after informational messages comes from.
4.11.2.5 Default prefix table -- SG.DPX
This is the default prefix table. By executing
XMOVEI T0, @SG.DPX
MOVEM T0, @SG.PFX
you will reset the LDH to use the default prefix table. You should not
attempt to change the contents of the default prefix table -- it may be
in write-protected memory.
4.11.2.6 Default suffix table -- SG.DSX
This is the default suffix table, very similar to SG.DPX.
4.12 DYNLIB Bootstrap
As much of DYNLIB as possible will actually reside in the RTL. Since
DYNLIB is used to bring in the RTL, "as much as possible" will be less
than "all".
Dynamic Library Specification Page 34
SOFTWARE CAPABILITIES 21 May 86
The subset of DYNLIB necessary to bring in the RTL will be available in
the file DYNBOO. All programs calling dynamic libraries must link with
DYNBOO.
5.0 PUBLICATIONS
DYNLIB development will include the preparation of two documents, "How
to write a Dynamic Library" and "How to call a dynamic library",
intended respectively for developers of dynamic libraries and users of
dynamic libraries.
These documents will be prepared by the engineering staff, there is no
funding for technical writers.
There is no plan to distribute these documents outside of Digital.
6.0 PACKAGING
The DYNLIB facility is being developed for Datatrieve. We want to make
it available to all layered products in the longer run. The first
release of DYNLIB will be packaged with Datatrieve-20 version 1.
7.0 INSTALLABILITY
DYNLIB will be installed as part of the installation of Datatrieve-20.
8.0 EASE OF USE
9.0 PERFORMANCE
Since DYNLIB is intended to be widely used as the basis for building
products out of layers of building-blocks, performance can be an
important issue. We believe, based on the usage of existing libraries,
that the vast majority of the interactions between a caller and a
package will be routine calls.
Calling a routine in a dynamic library will be done with a single PUSHJ
using one level of indirect addressing (unless the user writes code
requiring more to get to the transfer vector) after the first call
through any given LDLBLK.
Referring to an exported address will simply require one additional
level of indirection relative to referring to that address locally.
Since indirection is necessary to reference outside of the current
section anyway, DYNLIB will cost absolutely nothing on references after
the first.
Dynamic Library Specification Page 35
PERFORMANCE 21 May 86
The first reference to an address exported from a dynamic library will
potentially take a long time, since a GTJFN% is performed. This could
potentially require searching through thousands of file-names, if the
logical names used are defined wrong. There is also the matter of
creating a section and mapping the file into that section. On a
"reasonably" heavily loaded system, and assuming only moderately
perverse search lists, it could take 5 seconds to load a dynamic
library.
The other DYNLIB functions are very infrequently used and are not
performance-critical.
Many of the RTL functions have no performance requirements in the
Product Requirements document. This is because they aren't required in
and of themselves, but turn out to be necessary to meet other
requirements.
10.0 RELIABILITY
Because the first product using dynamic libraries to be seen by
customers, Datatrieve-20, is aimed at inexperienced users, it is
especially important that dynamic libraries not introduce any mysterious
(from the users' points of view) errors. Ideally, no errors should
occur. Next best is for errors to explain themselves clearly.
DYNLIB use rule: all programs which call dynamic libraries should check
for errors after each call, and present them to the user in a manner
compatible with the other user interactions made by the program.
11.0 MAINTAINABILITY
DYNLIB and its support procedures will be written in MACRO. I view this
as an unfortunate choice, but since DYNLIB is intended to become a
bundled part of the TOPS-20 operating system eventually, it should be
written in a language which purchasers of TOPS-20 sources can
understand. The tools for building libraries must be in macro anyway,
since they must be usable at all customer sites.
Most of the actual DYNLIB code will live in the RTL, with only a small
bootstrap routine to load the RTL on the first call to a dynamic
library.
DYNLIB will be autopatchable in the field. (What will it be autopatched
as part of? At first? Later?)
12.0 MAINTENANCE
Maintenance of this product will be performed by Software Engineering.
Dynamic Library Specification Page 36
MAINTENANCE 21 May 86
Updates will appear as necessary on the autopatch tapes.
13.0 COMPATIBILITY
13.1 Compatibility With Existing Libraries
An existing library that will run in an arbitrary non-zero section,
using no traps or interrupts, can be made a dynamic library simply by
writing a library definition and an appropriate master initialization
routine.
A library using traps and interrupts would be somewhat more difficult.
The degree of dificulty would depend on how the traps and interrupts
were used. It could still be quite simple, on the order of a day's work
by somebody who already understood dynamic libraries.
13.2 Product Compatibility
13.2.1 Dependency Issues
We must come to a consensus with the TOPS-20 monitor group on
interpretation of PDV's.
We must come to a consensus with the LINK and monitor groups on
LINK-provided memory maps.
13.3 Standards Conformance
13.4 Internationalization
No requirements in this area.
14.0 EVOLVABILITY
A Monitor DYNLIB facility could be written which would replace DYNBOO.
This would, I hope, be relatively simple. All the rest of DYNLIB
version would would be preserved, and performance would improve
somewhat.
15.0 COSTS
DYNLIB is being developed as part of the Datatrieve-20 project.
We hope to limit the development of DYNLIB to 4 man-months (including
all time spent from writing specification to field-test entry).
Dynamic Library Specification Page 37
TIMELINESS 21 May 86
16.0 TIMELINESS
The product must be ready to field-test and ship along with
Datatrieve-20.
17.0 CONSTRAINTS AND TRADES-OFF
Ease of conversion of an existing library is more important than keeping
the call overhead of that library within the bounds specified. However,
new libraries implemented according to the instructions to be developed
as part of DYNLIB must meet the call overhead limits. There may be
different techniques for defining a new dynamic library and a dynamic
interface to an existing library.
18.0 APPROVAL PROCESS
DYNLIB is being developed within the Datatrieve-20 project, but will
probably be used by many other projects. The normal approval process as
applied to Datatrieve-20 probably will not give sufficient visibility to
DYNLIB to ensure that necessary feedback from other groups is received.
Special efforts will be made to circulate DYNLIB documents to project
leaders and supervisors throughout LSG Software Engineering. Selected
consultant-level people within the group will be approached individually
for their comments.