[PATCH] xaudio2_7: Also preserve %ebx in call_on_voice_processing_pass_start().

[Andrew Eikum]

I'm not the right person to review the assembly, but the concept seems
fine and it doesn't break the build or tests for me.

Signed-off-by: Andrew Eikum <aeikum at codeweavers.com>

On Thu, Apr 11, 2019 at 11:30:50AM +0300, Paul Gofman wrote:
> It is tested that EBX register is not preserved by
> IXAudio2VoiceCallback_OnVoiceProcessingPassStart callback
> in League of Legends. It doesn't lead to crash in the
> present xaudio, while it might still be a potential issue.
> 
> Details are in https://bugs.winehq.org/show_bug.cgi?id=46870, while
> that bug is not dedicated to this specific issue.
> 
> Signed-off-by: Paul Gofman <gofmanp at gmail.com>
> ---
>  dlls/xaudio2_7/xaudio_dll.c | 9 +++++++--
>  1 file changed, 7 insertions(+), 2 deletions(-)
> 
> diff --git a/dlls/xaudio2_7/xaudio_dll.c b/dlls/xaudio2_7/xaudio_dll.c
> index 18306a1603..da34e480c1 100644
> --- a/dlls/xaudio2_7/xaudio_dll.c
> +++ b/dlls/xaudio2_7/xaudio_dll.c
> @@ -41,7 +41,8 @@
>  WINE_DEFAULT_DEBUG_CHANNEL(xaudio2);
>  
>  #if XAUDIO2_VER != 0 && defined(__i386__)
> -/* EVE Online uses an OnVoiceProcessingPassStart callback which corrupts %esi. */
> +/* EVE Online uses an OnVoiceProcessingPassStart callback which corrupts %esi;
> + * League of Legends uses a callback which corrupts %ebx. */
>  #define IXAudio2VoiceCallback_OnVoiceProcessingPassStart(a, b) call_on_voice_processing_pass_start(a, b)
>  extern void call_on_voice_processing_pass_start(IXAudio2VoiceCallback *This, UINT32 BytesRequired);
>  __ASM_GLOBAL_FUNC( call_on_voice_processing_pass_start,
> @@ -54,13 +55,17 @@ __ASM_GLOBAL_FUNC( call_on_voice_processing_pass_start,
>                    __ASM_CFI(".cfi_rel_offset %esi,-4\n\t")
>                     "pushl %edi\n\t"
>                    __ASM_CFI(".cfi_rel_offset %edi,-8\n\t")
> +                   "pushl %ebx\n\t"
> +                  __ASM_CFI(".cfi_rel_offset %ebx,-12\n\t")
>                     "subl $8,%esp\n\t"
>                     "pushl 12(%ebp)\n\t"     /* BytesRequired */
>                     "pushl 8(%ebp)\n\t"      /* This */
>                     "movl 8(%ebp),%eax\n\t"
>                     "movl 0(%eax),%eax\n\t"
>                     "call *0(%eax)\n\t"      /* This->lpVtbl->OnVoiceProcessingPassStart */
> -                   "leal -8(%ebp),%esp\n\t"
> +                   "leal -12(%ebp),%esp\n\t"
> +                   "popl %ebx\n\t"
> +                   __ASM_CFI(".cfi_same_value %ebx\n\t")
>                     "popl %edi\n\t"
>                     __ASM_CFI(".cfi_same_value %edi\n\t")
>                     "popl %esi\n\t"
> -- 
> 2.20.1
> 
> 
>