[PATCH][BZ #1349] Return requested size for malloc_usable_size when MALLOC_CHECK_ > 0

[Siddhesh Poyarekar]

Hi,

malloc_usable_size returns the usable size in an allocated chunk, which
may be >= the requested size. In the case of MALLOC_CHECK_ being
exported to > 0 however, only the requested size is usable, since a
magic value is written at the end of the request size to trap writes
beyond request bounds. Hence, when MALLOC_CHECK_ is exported to > 0,
malloc_usable_size() should return the request size. The attached patch
does exactly that.

There is also a test case included in the patch to verify that the
problem is fixed. I have verified on Fedora-16 x86_64 that this does
not cause any regressions.

Regards,
Siddhesh

ChangeLog:

	* malloc/Makefile (tests): Add tst-malloc-usable test case.
	(tst-malloc-usable-ENV): Set environment for test case.
	* malloc/hooks.c (malloc_check_get_size): New function to get
	requested size.
	* malloc/malloc.c (musable): Use malloc_check_get_size.
	* malloc/tst-malloc-usable.c: New test case.
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