On: Clang emits memcpy for std::swap, which can introd...

[majewsky]

The second one sounds like big fun when you LD_PRELOAD a different memcpy (say, for debugging purposes) and spend hours and hours trying to figure out why it is not being called.

[boulos → majewsky]

Yes, it's a nightmare, particularly on OS X with its funny loader semantics that make replacing malloc and free correctly very painful. For example, you can easily LD_PRELOAD your way out of malloc() but did you remember that asprintf also calls an allocation routine and won't use your new malloc? Enjoy.

[comex → boulos]

Hmm, why won't it? Maybe in the past when asprintf and malloc were located in the same dylib, since OS X dylibs generate direct calls to other public functions in the same image (rather than going through the PLT as GNU does by default), but for many years /usr/lib/libSystem.B.dylib has been split into several reexported libraries in /usr/lib/system, so there shouldn't be an issue there. Probably better to use this technique though (should still work in the latest version but needs mprotect):

http://eatmyrandom.blogspot.com/2010/03/mallocfree-intercept...

[ktRolster → boulos]

For debugging purposes, it can sometimes be easier to include a header file "mem_debug.h" or whatever, and redefine malloc:

  >#define malloc(a) debug_malloc(a, __FILE__, __LINE__)
  >#define free(a)   debug_free(a, __FILE__, __LINE__)
  >.
  >.
  >.

Then in your debug_malloc() function you can track where every allocation took place. Not always applicable but nice when it works.

[astrange → boulos]

malloc is set up to be specifically overridable so that guardmalloc(3)* will work. Are you saying asprintf doesn't work with guardmalloc?

* check it out, I used a man reference, am I a professional UNIX developer yet?

[achamayou → majewsky]

GCC does the exact same thing, and it can be turned off with -fno-builtin.