Re: [PATCH 1/1] target/ppc: fix ELFv2 signal handler endianness

[Laurent Vivier <laurent@vivier.eu>]

Le 15/03/2020 à 16:52, Vincent Fazio a écrit :
> From: Vincent Fazio <vfazio@gmail.com>
> 
> In ELFv2, function pointers are entry points and are in host endianness.

"host endianness" is misleading here. "target endianness" is better.

> 
> Previously, the signal handler would be swapped if the target CPU was a
> different endianness than the host. This would cause a SIGSEGV when
> attempting to translate the opcode pointed to by the swapped address.

This is correct.

>  Thread 1 "qemu-ppc64" received signal SIGSEGV, Segmentation fault.
>  0x00000000600a9257 in ldl_he_p (ptr=0x4c2c061000000000) at qemu/include/qemu/bswap.h:351
>  351        __builtin_memcpy(&r, ptr, sizeof(r));
> 
>  #0  0x00000000600a9257 in ldl_he_p (ptr=0x4c2c061000000000) at qemu/include/qemu/bswap.h:351
>  #1  0x00000000600a92fe in ldl_be_p (ptr=0x4c2c061000000000) at qemu/include/qemu/bswap.h:449
>  #2  0x00000000600c0790 in translator_ldl_swap at qemu/include/exec/translator.h:201
>  #3  0x000000006011c1ab in ppc_tr_translate_insn at qemu/target/ppc/translate.c:7856
>  #4  0x000000006005ae70 in translator_loop at qemu/accel/tcg/translator.c:102
> 
> Now, no swap is performed and execution continues properly.
> 
> Signed-off-by: Vincent Fazio <vfazio@gmail.com>
> ---
>  linux-user/ppc/signal.c | 10 +++++++---
>  1 file changed, 7 insertions(+), 3 deletions(-)
> 
> diff --git a/linux-user/ppc/signal.c b/linux-user/ppc/signal.c
> index 5b82af6cb6..c7f6455170 100644
> --- a/linux-user/ppc/signal.c
> +++ b/linux-user/ppc/signal.c
> @@ -567,9 +567,13 @@ void setup_rt_frame(int sig, struct target_sigaction *ka,
>          env->nip = tswapl(handler->entry);
>          env->gpr[2] = tswapl(handler->toc);
>      } else {
> -        /* ELFv2 PPC64 function pointers are entry points, but R12
> -         * must also be set */
> -        env->nip = tswapl((target_ulong) ka->_sa_handler);
> +        /*
> +         * ELFv2 PPC64 function pointers are entry points and are in host
> +         * endianness so should not to be swapped.

"target endianness"

> +         *
> +         * Note: R12 must also be set.
> +         */
> +        env->nip = (target_ulong) ka->_sa_handler;

The cast is not needed: nip and _sa_handler are abi_ulong.

>          env->gpr[12] = env->nip;
>      }
>  #else
> 

If you repost with the fix I've reported above you can add my:

Reviewed-by: Laurent Vivier <laurent@vivier.eu>

Thanks,
Laurent