The LINK command

Preamble

Owing to incompatibilities between V2 and V3 compilers, two variants of this command exist:

LINK2 for modules compiled by version 2 compilers,
LINK3 for modules compiled by version 3 compilers.

At present (September 1986), LINK is equivalent to LINK2.

The parameters to the commands consist of a list of input module names and a single name to be given to the output module. The file-name extension .MOB is assumed for all of the names.

Background

The LINK command combines two or more compiled M68000 program modules into a single program module. The cross-references between the input modules are discharged so that they no longer require to be satisfied at execution time.

One of the reasons for carrying out this operation is to reduce the time overhead in loading a program made up of a large number of fixed modules. Another is to make a program more self-contained and less dependent on the module environment in which it is run. Use of it involves sacrificing the flexibility of load-time linking and convenience of individual module development, so that it is appropriate mainly for stable program suites. Note also that, in the case of modules compiled with the V3 diagnostic compilers, that DIAGNOSTIC INFORMATION IS LOST in the linking process.

If the first input module is a main program, the resultant module will also be a main program; otherwise the resultant module will simply be a library of external procedures.

The import list of the output module will consist of all those imports appearing in the import lists of the input modules which are NOT satisfied by internal cross-reference.

By default, the export list of the output module will consist of all those exports which are NOT used to satisfy internal cross-references.

The user may modify this behaviour by requesting that an export should either be included irrespective (even if used internally) or excluded irrespective (even if not used internally).

Using LINK2

} LINK2 Mainfile,Auxfile1,.../Outfile-Options

Up to 19 auxiliary files may be specified.

Parameters

Mainfile
The object file containing the main module.

Auxfile1..19
Object files containing further modules.

Outfile
The file to receive the output object module. If omitted, the
output file will have the same name as (i.e. will replace)
the main input file.

Options

Include, Exclude

These parameters, if present, are either "*" or a filename. If "*", this means all exports are to be in/excluded in the output, if a filename (which may be the terminal (":")), then a list of export names to be in/excluded are read from the specified file.

If one is specified as "*", it will be processed before the other, so that the other is always a list of exceptions to the first. Specifying "*" for both is daft.

Dynamic

If this boolean parameter is specified, any dynamic references are left as such. Otherwise these are converted into ordinary external references.

Auto

If this boolean parameter is specified, the linker will search the current external dictionary to determine which object files are required. This eliminates the need to type in long lists of object filenames, provided the ones needed have been INSTALLed.

Disregard

This parameter (relevant only when -auto is specified), is a filename. The file contains a list of object file names NOT to be inculded by the automatic scanning. The default DISREGARD-file is UTILS:LINK.DAT which causes the linker to exclude most of the standard run time libraries which are normally preloaded (or at least installed) on all machines.

Restrictions

Part-linking

Part-linking a collection of libraries to form a new library is not recommended, especially if the resultant library is intended to be linked later with something else. It is therefore suggested that the MAINFILE should always be a main program.

More precisely, you are likely to get into trouble if any included exports are not from the first module of the parameter list (Mainfile).

In other words, it should be OK to part-link A with B and C, provided that, at run-time, the exports made by B and C are only used by A, B, or C, not by the main program or other modules loaded with it.

Dynamic references

Believed dodgy. Hence the -DYNAMIC parameter is off by default.

Size of output file

Things may go wrong if the combined size of the output code and data areas exceeds 64K.

Using LINK3

Parameters may be provided as part of the command line. If omitted from the command, they will be requested on subsequent lines, one module per line.

The output file name is mandatory. The command line is NOT processed by PAM.

For example

} LINK3 MAIN,SUB1,SUB2/NEWMAIN

or
} LINK3
1st file: MAIN
2nd file: SUB1
3rd file (or *): SUB2
4th file (or *): *
New file: NEWMAIN

Include, Exclude

Inclusions and exclusions are specified by means of a + (inclusion) or - (exclusion) followed by an export name (or * for all). For example
} LINK
1st file: MAIN+*
2nd file: SUB1+PARSE-DIAGNOSE
3rd file (or *): SUB2-*+INITIALISE
etc

Notes

The process of linking does not alter the main code of the modules, and the internally linked calls therefore use the same call sequence as normally linked externals.

A linked module is itself acceptable as input to the LINK program.

If an import name could be satisfied by more than one export name (by virtue of the presence of multiple exports with the same name) the one that is used to satisfy the reference is not guaranteed to match that which would be selected by load-time linking. In general, this means that such duplication should be avoided.

Multiple occurrences of the same (unsatisfied) import name will appear multiply in the linked file.

Diagnostic tables do not survive linking.

Automatic linking (as with LINK2) is not available.

view:link printed on 15/02/89 at 21.49

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