Re: [Qemu-devel] [PATCH for-4.0] target/ppc: Fix QEMU crash with stxsdx

[Mark Cave-Ayland]

On 27/03/2019 18:12, Greg Kurz wrote:

> I've been hitting several QEMU crashes while running a fedora29 ppc64le
> guest under TCG. Each time, this would occur several minutes after the
> guest reached login:
> 
> Fedora 29 (Twenty Nine)
> Kernel 4.20.6-200.fc29.ppc64le on an ppc64le (hvc0)
> 
> Web console: https://localhost:9090/
> 
> localhost login:
> tcg/tcg.c:3211: tcg fatal error
> 
> This happens because a bug crept up in the gen_stxsdx() helper when it
> was converted to use VSR register accessors by commit 8b3b2d75c7c04
> "target/ppc: introduce get_cpu_vsr{l,h}() and set_cpu_vsr{l,h}() helpers
> for VSR register access".
> 
> The code creates a temporary, passes it directly to gen_qemu_st64_i64()
> and then to set_cpu_vrsh()... which looks like this was mistakenly
> coded as a load instead of a store.
> 
> Reverse the logic: read the VSR to the temporary first and then store
> it to memory.
> 
> Fixes: 8b3b2d75c7c0481544e277dad226223245e058eb
> Signed-off-by: Greg Kurz <address@hidden>
> ---
>  target/ppc/translate/vsx-impl.inc.c |    2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/target/ppc/translate/vsx-impl.inc.c 
> b/target/ppc/translate/vsx-impl.inc.c
> index 508e9199c8df..489b2436e49f 100644
> --- a/target/ppc/translate/vsx-impl.inc.c
> +++ b/target/ppc/translate/vsx-impl.inc.c
> @@ -356,8 +356,8 @@ static void gen_##name(DisasContext *ctx)                 
>     \
>      gen_set_access_type(ctx, ACCESS_INT);                     \
>      EA = tcg_temp_new();                                      \
>      gen_addr_reg_index(ctx, EA);                              \
> +    get_cpu_vsrh(t0, xS(ctx->opcode));                        \
>      gen_qemu_##operation(ctx, t0, EA);                        \
> -    set_cpu_vsrh(xS(ctx->opcode), t0);                        \
>      tcg_temp_free(EA);                                        \
>      tcg_temp_free_i64(t0);                                    \
>  }

Gah, yes - I remember at one point having to double check the get/set direction 
but
obviously my brain and fingers got the better of me here. Apologies for the
inconvenience.

Reviewed-by: Mark Cave-Ayland <address@hidden>


ATB,

Mark.