[cc]mc |
.hd snplnk "snap shared library dynamic links" 09/10/84
x snplnk 1/<segment> [2/1]
.ds
'Snplnk' is a Primos-executable routine that scans a given segment
looking for dynamic library links (DYNT's) and forces the Primos
ring 3 pointer fault handler to resolve the address. After 'snplnk'
has been run on a segment, the segment may be shared non-writable
if it contains pure code. It is actually meant to be run from Primos
during library initialization rather than from SWT. <Segment> is the
desired segment to snap as an octal number, and the "2/1" causes
'snplnk' to print the name of the routine it is about to attempt to
resolve along with the location of the pointer in the segment.
.sp
To use 'snplnk', the information should be installed in the segment
and the segment should then be left writable. 'Snplnk' is then run
on the segment and the segment can then be made non-writable.
As an example, Georgia Tech has a file that is run at boot time
called "swt.share.comi" that installs the SWT subsystem. The file
contains:
.sp
.nf
.in +5
/* SWT.SHARE.COMI, Share Software Tools Subsystem
/*    Last modified: 06/11/84

OPR 1
SHARE SYSTEM>SW2035 2035 700  /* Library
SHARE SYSTEM>SH2030 2030 700  /* Shell library
SHARE SYSTEM>ST2030 2030 700  /* SWT Initialization program
SHARE SYSTEM>SE2031 2031 700  /* Screen Editor
R SYSTEM>SW4000 1/1           /* Install the Library
R SYSTEM>SH4000 1/5           /* Shell library
R SYSTEM>INITSWT

SNPLNK 1/2030; SHARE 2030 600 /* Snap links and make the
SNPLNK 1/2031; SHARE 2031 600 /* segments not writeable
SNPLNK 1/2035; SHARE 2035 600
OPR 0

CO -CONTINUE 6
CO -END
.sp
.fi
.in -5
The command "SNPLNK 1/2035; SHARE 2035 600" first snaps all the
dynamic links in segment 2035 (the shared standard library) and
then makes the segment non-writable. This prevents a user from
altering the segment whether malicious or otherwise.
.me
"A register setting missing" for missing <segment>
.sp
"Segment range is 2030-2037" for a segment out of that range
.bu
Should be written to use reasonable argument handling.
.sp
Gets a pointer fault when trying to snap a link to a routine that
does not exist.
.sp
The program attempts to be as intelligent as possible about what a link
is and is not but mistakes can theoretically happen.
[cc]mc