Provide consistent behaviour for memchr(_,_,0)

Provide consistent behaviour for memchr(_,_,0)

A memchr() search of a zero-byte range returns an undefined value.
On arm32 it always returns NULL, but on arm64 it does not.  This
causes random crashes while reading /proc/self/maps when loading the
64-bit libchrome.

Fix by setting the value to which memchr() assigns to NULL if the
search range is zero bytes.  There are three calls to memchr().  Two
of them could encounter this; the third is safe.

BUG=394306
Committed: https://src.chromium.org/viewvc/chrome?view=rev&revision=284693

[rmcilroy, 2014-07-22 09:16:36]

lgtm with optional suggestion.

https://codereview.chromium.org/405153002/diff/1/third_party/android_crazy_li...
File third_party/android_crazy_linker/src/src/crazy_linker_proc_maps.cpp
(right):

https://codereview.chromium.org/405153002/diff/1/third_party/android_crazy_li...
third_party/android_crazy_linker/src/src/crazy_linker_proc_maps.cpp:67: tok_end
= NULL;
Optional suggestion - I'm not sure if the crazy linker has a useful utility
class, but could we factor this out to a separate helper function (e.g.,
safe_memchr) which also automatically does the const char* static_cast?

[simonb (inactive), 2014-07-22 12:06:38]

The CQ bit was checked by simonb@chromium.org

[commit-bot: I haz the power, 2014-07-22 12:07:01]

CQ is trying da patch. Follow status at
 https://chromium-status.appspot.com/cq/simonb@chromium.org/405153002/1

[commit-bot: I haz the power, 2014-07-22 16:12:44]

Change committed as 284693