Re: [DynInst_API:] Problems in instrumenting malloc

[John Detter <jdetter@xxxxxxxx>]

Martijn,

What are you using as your mutatee? e.g. what is the command you're using to run the tutorial?

-- John

On 7/18/2016 8:50 AM, Martijn wrote:

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

   443: 0000000000083550   414 FUNC    GLOBAL DEFAULT   13 __libc_malloc@@GLIBC_2.2.5
   550: 0000000000086e70    24 FUNC    WEAK   DEFAULT   13 malloc_info@@GLIBC_2.10
   820: 0000000000086560   474 FUNC    WEAK   DEFAULT   13 malloc_stats@@GLIBC_2.2.5
   992: 0000000000083850   539 FUNC    WEAK   DEFAULT   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
                 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

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