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

[Richard Henderson <rth@twiddle.net>]

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<peter.maydell@linaro.org>
> ---
>   linux-user/elfload.c | 23 ++++++++++++-----------
>   1 file changed, 12 insertions(+), 11 deletions(-)

Reviewed-by: Richard Henderson <rth@twiddle.net>
Tested-by:  Richard Henderson <rth@twiddle.net>


r~