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mallocwatch breaks on a c++ program #59

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sudhackar opened this issue Mar 27, 2019 · 0 comments · Fixed by #60
Closed

mallocwatch breaks on a c++ program #59

sudhackar opened this issue Mar 27, 2019 · 0 comments · Fixed by #60

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@sudhackar
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If malloc is called in libstdc++ while loading before preeny_mallocwatch_orig has been called from call_init.part it crashes as such

Program received signal SIGSEGV (fault address 0x0)
pwndbg> bt
#0  0x0000000000000000 in ?? ()
#1  0x00007ffff77d0ea6 in malloc (size=72704) at /tmp/preeny/src/mallocwatch.c:30
#2  0x00007ffff72d59c0 in ?? () from /usr/lib/x86_64-linux-gnu/libstdc++.so.6
#3  0x00007ffff7de879a in call_init (l=<optimized out>, argc=argc@entry=1, argv=argv@entry=0x7fffffffdff8, env=env@entry=0x7fffffffe008) at dl-init.c:72
#4  0x00007ffff7de88ab in call_init (env=0x7fffffffe008, argv=0x7fffffffdff8, argc=1, l=<optimized out>) at dl-init.c:30
#5  _dl_init (main_map=0x7ffff7ffe170, argc=1, argv=0x7fffffffdff8, env=0x7fffffffe008) at dl-init.c:120
#6  0x00007ffff7dd9c5a in _dl_start_user () from /lib64/ld-linux-x86-64.so.2
#7  0x0000000000000001 in ?? ()
#8  0x00007fffffffe33d in ?? ()
#9  0x0000000000000000 in ?? ()

Fix should be pretty simple, checking if original_mallocand family is actually set or not and then calling preeny_mallocwatch_orig

preeny/src/mallocwatch.c

Line 30 in 36b1874

void *r = original_malloc(size);

I'll send a PR.
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Adding check if dlsym was called before calling malloc+free family.
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@sudhackar