Loads the global symbols contained in the specified file into the
SDA symbol table.
Format
READ {/EXECUTIVE [directory spec]
| /FORCE filespec [/RELOCATE =expression |
/SYMVA=expression]
| /IMAGE filespec
| filespec}
[ /[NO]LOG]
1 – Parameters
directory-spec
Name of the directory containing the loadable images of the
executive. This parameter defaults to SDA$READ_DIR, which is a
search list of SYS$LOADABLE_IMAGES, SYS$LIBRARY, and SYS$SYSTEM.
filespec
Name of the device, directory, and file from which you want to
read global symbols. The filespec defaults to SYS$DISK:[default-
dir]filename.type, where SYS$DISK and [default-dir] represent
the disk and directory specified in your last DCL command SET
DEFAULT. If no type has been given in filespec, SDA first tries
.STB and then .EXE.
If no device or directory is given in the file specification, and
the file specification is not found in SYS$DISK:[default_dir],
then SDA attempts to open the file SDA$READ_DIR:filename.type. If
no type has been given in filespec, SDA first tries .STB and then
.EXE.
If the file name is the same as that of an execlet or image, but
the symbols in the file are not those of the execlet or image,
then you must use the /FORCE qualifier, and optionally /RELOCATE
and /SYMVA qualifiers, to tell SDA how to interpret the symbols
in the file.
The READ command accepts quoted filenames for access to images on
ODS-5 disks with lowercase or compound characters in their names.
2 – Qualifiers
2.1 /EXECUTIVE
/EXECUTIVE directory-spec
Reads into the SDA symbol table all global symbols and global
entry points defined within all loadable images that make up the
executive. For all the execlets in the system, SDA reads the .STB
or .EXE files in the requested directory.
2.2 /FORCE
/FORCE filespec
Forces SDA to read the symbols file, regardless of what other
information or qualifiers are specified. If you do not specify
the /FORCE qualifier, SDA may not read the symbols file if the
specified filespec matches the image name in either the executive
loaded images or the current processes activated image list, and
one of the following conditions is true:
o The image has a symbols vector (is a shareable image), and
a symbols vector was not specified with the /SYMVA or /IMAGE
qualifier.
o The image is sliced, and slicing information was not provided
with the /IMAGE qualifier.
o The shareable or executive image is not loaded at the same
address it was linked at, and the relocation information was
not provided with either the /IMAGE or /RELOCATE qualifier.
The use of /FORCE [/SYMVA=addr][/RELOCATE=addr] filespec is a
variant of the /IMAGE qualifier and avoids fixing up the symbols
to match an image of the same name.
2.3 /IMAGE
/IMAGE filespec
Searches the executive loaded image list and the current process
activated image list for the image specified by filespec. If
the image is found, the symbols are read in using the image
symbol vector (if there is one) and either slicing or relocation
information.
This is the preferred way to read in the .STB files produced
by the linker. These .STB files contain all universal symbols,
unless SYMBOL_TABLE=GLOBAL is in the linker options file, in
which case the .STB file contains all universal and global
symbols.
2.4 /LOG
/LOG
/NOLOG (D)
The /LOG qualifier causes SDA to output the %SDA-I-READSYM
message for each symbol table file it reads. By default, these
messages are suppressed. You can specify /LOG and /NOLOG with any
other combination of parameters and qualifiers.
2.5 /RELOCATE
/RELOCATE=expression
Changes the relative addresses of the symbols to absolute
addresses by adding the value of expression to the value of
each symbol in the symbol table file to be read. This qualifier
changes those addresses to absolute addresses in the address
space into which the dump is mapped.
The relocation only applies to symbols with the relocate flag
set. All universal symbols must be found in the symbol vector for
the image. All constants are read in without any relocation.
If the image is sliced (image sections are placed in memory at
different relative offsets than how the image is linked), then
the /RELOCATE qualifier does not work. SDA compares the file
name used as a parameter to the READ command against all the
image names in the executive loaded image list and the current
processes activated image list. If a match is found, and that
image contains a symbol vector, an error results. At this point
you can either use the /FORCE qualifier or the /IMAGE qualifier
to override the error.
2.6 /SYMVA
/SYMVA=expression
Informs SDA whether the absolute symbol vector address is for
a shareable image (SYS$PUBLIC_VECTORS.EXE) or base system image
(SYS$BASE_IMAGE.EXE). All symbols found in the file with the
universal flag are found by referencing the symbol vector (that
is, the symbol value is a symbol vector offset).
3 – Description
The following MACRO program can be used to obtain symbols in
addition to those in SYS$BASE_IMAGE.EXE:
.TITLE GLOBALS
$PHDDEF GLOBAL ; Process header definitions
$DDBDEF GLOBAL ; Device data block
$UCBDEF GLOBAL ; Unit control block
$VCBDEF GLOBAL ; Volume control block
$ACBDEF GLOBAL ; AST control block
$IRPDEF GLOBAL ; I/O request packet
; More can be inserted here
.END
Use the command below to generate an object module file
containing the globals defined in the program.
$MACRO GLOBALS+SYS$LIBRARY:LIB/LIBRARY /OBJECT=GLOBALS.STB
SDA can also read symbols from an image .EXE or .STB produced by
the linker. The STB and EXE files only contain universal symbols.
The STB file, however, can be forced to have global symbols for
the image if the SYMBOL_TABLE=GLOBAL option is used in the linker
options file.
If you do not specify a file type, .STB is used by default. If a
.STB file is not found, SDA then tries a .EXE file.
A number of ready-built symbol table files ship with OpenVMS
Alpha. They can be found in the directory SYS$LOADABLE_IMAGES,
and all have names of the form xyzDEF.STB. Of these files, SDA
automatically reads REQSYSDEF.STB on activation. The symbols in
the other files can be added to SDA's symbol table using the READ
command.