Re: [Qemu-devel] [PATCH] linux-user: Put PPC AT_IGNOREPPC auxv entries in the right place

[Peter Maydell]

On 27 June 2017 at 19:05, Richard Henderson <address@hidden> wrote:
> On 06/27/2017 09:49 AM, Peter Maydell wrote:
>>
>> The 32-bit PPC auxv is a bit complicated because in the
>> mists of time it used to be 16-aligned rather than directly
>> after the environment. Older glibc versions had code to
>> try to probe for whether it needed alignment or not:
>>
>> https://sourceware.org/git/?p=glibc.git;a=blob;f=sysdeps/unix/sysv/linux/powerpc/dl-sysdep.c;hb=e84eabb3871c9b39e59323bf3f6b98c2ca9d1cd0
>> and the kernel has code which puts some magic entries at
>> the bottom to ensure that the alignment probe fails:
>>
>> http://elixir.free-electrons.com/linux/latest/source/arch/powerpc/include/asm/elf.h#L158
>>
>> QEMU has similar code too, but it was broken by commit
>> 7c4ee5bcc82e64, which changed elfload.c from filling in
>> the auxv starting at the highest address and working down
>> to starting at the lowest address and working up. This
>> means that the ARCH_DLINFO hook must now be invoked first
>> rather than last, and the entries in it for PPC must
>> be reversed so that the magic AT_IGNOREPPC entries come
>> at the lowest address in the auxv as they should.
>>
>> The effect of this was that if running a guest binary that
>> used an old glibc with the alignment probing the guest ld.so
>> code would segfault if the size of the guest environment and
>> argv happened to put the auxv at an address that triggered
>> the alignment code in the guest glibc.
>>
>> Signed-off-by: Peter Maydell<address@hidden>
>> ---
>>   linux-user/elfload.c | 23 ++++++++++++-----------
>>   1 file changed, 12 insertions(+), 11 deletions(-)
>
>
> Reviewed-by: Richard Henderson <address@hidden>
> Tested-by:  Richard Henderson <address@hidden>

Thanks; applied directly to master since this has been
causing my mergebuild tests to fail (some recent environment
change result in it triggering this week...)

thanks
-- PMM