[Bug rtl-optimization/60947] [4.9/4.10 Regression] Unable to handle kernel paging request (linux kernel 2.6.28.9) with gcc 4.9 release

[mikpelinux at gmail dot com]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=60947

--- Comment #16 from Mikael Pettersson <mikpelinux at gmail dot com> ---
(In reply to amker from comment #15)
> Well, only thing suspicious that I can see, the memset function is a special
> implementation and not from C standard library.  Basically it doesn't need
> to follow the standard, which means the return value could be something else
> other than the passed in pointer.  Though I doubt it would actually break
> the standard.
> 
> So YuFan, could you help look into implementation of memset to see if it
> acts as expected?
> 
> Thanks.

I recall seeing reports of the Linux/ARM kernel being miscompiled by gcc-4.8
(or so) a while ago, and it was traced to an in-kernel memset() (or related
mem/str-function) implementation not following the same return value convention
as the normal user-space version.  The problem is that newer gcc:s optimize
some mem/str-functions based on those return value conventions, so things
broke.  The 2.6.28 kernel is ancient, so it's not at all surprising it won't
work when compiled by non-ancient gcc:s.