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Re: pgrep and pkill (any? arguments): cannot allocate 4294967295 bytes

From: Paul Dufresne
Subject: Re: pgrep and pkill (any? arguments): cannot allocate 4294967295 bytes
Date: Tue, 02 Feb 2021 11:11:41 -0500
User-agent: Zoho Mail

Sorry, because in previous posts, it seems code was not exactly the same as source code.

I now came to the following conclusion:
main (argc=2, argv=0x1032e24) at pgrep.c:935
935             procs = select_procs (&num);
(gdb) s
select_procs (num=0x1032d60) at pgrep.c:489
489     {
(gdb) s
494             pid_t saved_pid = 0;                      /* for new/old support */
(gdb) s
495             int matches = 0;
(gdb) s
496             int size = 0;
(gdb) s
498             pid_t myself = getpid();
(gdb) s
499             struct el *list = NULL;
(gdb) p myself
$1 = 19024
(gdb) s
500             long cmdlen = sysconf(_SC_ARG_MAX) * sizeof(char);
(gdb) p _SC_ARG_MAX
$2 = _SC_ARG_MAX
(gdb) p sizeof(char)
$3 = 1
(gdb) p sysconf(_SC_ARG_MAX)
'sysconf' has unknown return type; cast the call to its declared return type
(gdb) s
501             char *cmdline = xmalloc(cmdlen);
(gdb) p cmdlen
$4 = -1

I am convinced sysconf(_SC_ARG_MAX) returned -1 (I believe in unsigned value 4294967295)... and it try to allocate that value.
So -1 surely means error for sysconf.

Need to figure out what sysconf(_SC_ARG_MAX) is....

From: https://www.qnx.com/developers/docs/6.4.1/neutrino/lib_ref/s/sysconf.html
Maximum length of arguments for the exec*() functions, in bytes, including environment data.

Now... for the details how I was able to get there... And I feel I may not have been doing it the most effective way.
I used info from: https://wiki.debian.org/HowToGetABacktrace
did something like:
#mkdir build_procps
#cd build_procps
#DEB_BUILD_OPTIONS="nostrip noopt" apt -b source procps
root@kibar:~/procps-3.3.16# file /usr/bin/pgrep
/usr/bin/pgrep: ELF 32-bit LSB pie executable, Intel 80386, version 1 (SYSV), dynamically linked, interpreter /lib/ld.so, BuildID[sha1]=d8ba18308f63edfc63d24003d9dda11fcfa8e75e, for GNU/Hurd 0.0.0, with debug_info, not stripped

[made sure with debug_info, not stripped is there]

#cd some new (empty) directory
#apt-get source procps
# cd procps-3.3.16/

#gdb /usr/bin/pgrep

(gdb) set args something_not_existing
(gdb) break main
(gdb) run
s [for step] repeated many times until I get on the right line, as shown in beginning of this message

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