Bug#1078128: libc6: mtrace() + malloc() do not generate data

[Vincent Lefevre <vincent@vinc17.net>]

Package: libc6
Version: 2.39-6
Severity: normal

When testing the example given in the mtrace(3) man page,
no data are generated:

$ cat t_mtrace.c
#include <mcheck.h>
#include <stdio.h>
#include <stdlib.h>

int
main(void)
{
  mtrace();

  for (unsigned int j = 0; j < 2; j++)
    malloc(100);            /* Never freed--a memory leak */

  calloc(16, 16);             /* Never freed--a memory leak */
  exit(EXIT_SUCCESS);
}

$ cc -g t_mtrace.c -o t_mtrace
t_mtrace.c: In function ‘main’:
t_mtrace.c:11:5: warning: ignoring return value of ‘malloc’ declared with attribute ‘warn_unused_result’ [-Wunused-result]
   11 |     malloc(100);            /* Never freed--a memory leak */
      |     ^~~~~~~~~~~
t_mtrace.c:13:3: warning: ignoring return value of ‘calloc’ declared with attribute ‘warn_unused_result’ [-Wunused-result]
   13 |   calloc(16, 16);             /* Never freed--a memory leak */
      |   ^~~~~~~~~~~~~~
$ export MALLOC_TRACE=/tmp/t
$ ./t_mtrace
$ mtrace ./t_mtrace $MALLOC_TRACE
Cannot open mtrace data file at /bin/mtrace line 152, <locs> line 4.
$ ls $MALLOC_TRACE
ls: cannot access '/tmp/t': No such file or directory

-- System Information:
Debian Release: trixie/sid
  APT prefers unstable-debug
  APT policy: (500, 'unstable-debug'), (500, 'stable-updates'), (500, 'stable-security'), (500, 'stable-debug'), (500, 'proposed-updates-debug'), (500, 'unstable'), (500, 'testing'), (500, 'stable'), (1, 'experimental')
Architecture: amd64 (x86_64)

Kernel: Linux 6.7.12-amd64 (SMP w/16 CPU threads; PREEMPT)
Kernel taint flags: TAINT_WARN
Locale: LANG=C.UTF-8, LC_CTYPE=C.UTF-8 (charmap=UTF-8), LANGUAGE not set
Shell: /bin/sh linked to /usr/bin/dash
Init: systemd (via /run/systemd/system)
LSM: AppArmor: enabled

Versions of packages libc6 depends on:
ii  libgcc-s1  14.2.0-1

Versions of packages libc6 recommends:
ii  libidn2-0  2.3.7-2

Versions of packages libc6 suggests:
ii  debconf [debconf-2.0]  1.5.87
ii  glibc-doc              2.39-6
ii  libc-l10n              2.39-6
pn  libnss-nis             <none>
pn  libnss-nisplus         <none>
ii  locales                2.39-6

-- debconf information:
  glibc/disable-screensaver:
  glibc/kernel-not-supported:
  glibc/restart-services:
  glibc/upgrade: true
  glibc/kernel-too-old:
  glibc/restart-failed:
* libraries/restart-without-asking: true

-- 
Vincent Lefèvre <vincent@vinc17.net> - Web: <https://www.vinc17.net/>
100% accessible validated (X)HTML - Blog: <https://www.vinc17.net/blog/>
Work: CR INRIA - computer arithmetic / AriC project (LIP, ENS-Lyon)