[PATCH 2/2 Take-2][BZ #12416] Use stack boundaries from /proc/PID/maps to make stack executable

[Siddhesh Poyarekar]

On Wed, 25 Apr 2012 13:34:24 -0700 (PDT), Roland wrote:
> Perhaps it should work in a different way.  It's nasty to
> require /proc access, and all the io plus stdio overhead et al might
> make it more costly than another method.  It could use something like
> the mprotect-probing technique to locate the hole below the stack
> that linux/dl-execstack.c uses when PROT_GROWSDOWN is not available.

I have written a new patch based on this idea. I have consolidated the
mprotect-probing code into a function to make the code a bit cleaner,
since the same logic is being used repeatedly. I have also updated the
test case to not use procfs and use pthread_getattr_np instead. I have
verified (on x86_64) the test case with and without this fix. I have
also verified that there are no regressions in the testsuite due to
this fix.

Regards,
Siddhesh

ChangeLog:

2012-04-27  Siddhesh Poyarekar  <siddhesh@redhat.com>

	[BZ #12416]
	Based on idea by Roland McGrath.
	* elf/tst-execstack.c (do_test): Check that pthread_getattr_np
	returns the same end of stack before and after stack is made
	executable.
	* sysdeps/unix/sysv/linux/dl-execstack.c
	(_dl_make_stack_executable): Also mark pages below (or above if
	_STACK_GROWS_UP) as executable. Consolidate code to
	incrementally mark stack executable to ...
	(_incremental_make_stack_executable): ... a new function.
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