[DynInst_API:] Problems in instrumenting malloc

[Martijn <martijn@xxxxxxxxxxxxxxxxx>]

Hello,

I am looking at the DynInst API to instrument applications to detect memory errors. Very impressed with the platform independence of the API thus far.

Studying the maxarg.C tutorial code on http://www.paradyn.org/tutorial/ with DynInst 9.2.0 on Ubuntu 16.04 Desktop and gcc 5.3.1, I encounter two issues, the second blocking me:

1) The maxarg tutorial tries to add a snippet to malloc() in libc.so. It tries to find the malloc function in the module with substring "libc" using findModule(). As I understand the API, this will find the module of libc.so.6, but malloc() may well be implemented in a separate source file, and hence another module name. I corrected the example by first obtaining the libc.so.6 BPatch_object, and then using findFunction on the object, which walks over all modules in the libc.so.6. A findObject() convenience function on the BPatch_image would be nice here.

2) Still, the example cannot find the function malloc() in the libc object. obj->findFunction("malloc") works on all modules in the libc object, but fails to find malloc. It does work for free(), returning "__GI___libc_free" as the function name in /lib/x86_64-linux-gnu/libc-2.23.so.

malloc seems to be present in libc:

$ readelf -s /lib/x86_64-linux-gnu/libc-2.23.so | grep malloc

ÂÂ 443: 0000000000083550ÂÂ 414 FUNCÂÂÂ GLOBAL DEFAULTÂÂ 13 __libc_malloc@@GLIBC_2.2.5
ÂÂ 550: 0000000000086e70ÂÂÂ 24 FUNCÂÂÂ WEAKÂÂ DEFAULTÂÂ 13 malloc_info@@GLIBC_2.10
ÂÂ 820: 0000000000086560ÂÂ 474 FUNCÂÂÂ WEAKÂÂ DEFAULTÂÂ 13 malloc_stats@@GLIBC_2.2.5
ÂÂ 992: 0000000000083850ÂÂ 539 FUNCÂÂÂ WEAKÂÂ DEFAULTÂÂ 13 malloc_get_state@@GLIBC_2.2.5
 1088: 00000000003c3b10 8 OBJECT WEAK DEFAULT 33 __malloc_hook@@GLIBC_2.2.5
 1185: 0000000000083550 414 FUNC GLOBAL DEFAULT 13 malloc@@GLIBC_2.2.5
 1221: 00000000000845f0 498 FUNC WEAK DEFAULT 13 malloc_usable_size@@GLIBC_2.2.5
 1467: 0000000000086170 705 FUNC WEAK DEFAULT 13 malloc_trim@@GLIBC_2.2.5
 1787: 00000000003c57b0 8 OBJECT WEAK DEFAULT 34 __malloc_initialize_hook@@GLIBC_2.2.5
 2087: 00000000000856b0 1320 FUNC WEAK DEFAULT 13 malloc_set_state@@GLIBC_2.2.5

And my test program explicitly calls malloc:

$ nm -g test1/test |grep malloc
ÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂ U malloc@@GLIBC_2.2.5

Any ideas what I do wrong here to try to find and instrument malloc()? I hope you can help me further.

Thanks,

Martijn

martijn@xxxxxxxxxxxxxxxxx