[PATCH] ntdll: Do not override existing context's EAX when dispatching user APC.

[Gabriel Ivăncescu]

Fixes a regression introduced by 175a3649ba04daaad3f2b5b62d6bfe091d6a9e46,
which caused Winamp's in_wave module to crash when playing a wav file
(the previous behavior only changed EAX when there was no context).

Signed-off-by: Gabriel Ivăncescu 
---
 dlls/ntdll/unix/signal_i386.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/dlls/ntdll/unix/signal_i386.c b/dlls/ntdll/unix/signal_i386.c
index ff9d8a1..f2d58dc 100644
--- a/dlls/ntdll/unix/signal_i386.c
+++ b/dlls/ntdll/unix/signal_i386.c
@@ -1696,6 +1696,7 @@ struct apc_stack_layout * WINAPI setup_user_apc_dispatcher_stack( CONTEXT *conte
     {
         c.ContextFlags = CONTEXT_FULL;
         NtGetContextThread( GetCurrentThread(), &c );
+        c.Eax = STATUS_USER_APC;
         context = &c;
     }
     memmove( &stack->context, context, sizeof(stack->context) );
@@ -1704,7 +1705,6 @@ struct apc_stack_layout * WINAPI setup_user_apc_dispatcher_stack( CONTEXT *conte
     stack->arg1 = arg1;
     stack->arg2 = arg2;
     stack->func = func;
-    stack->context.Eax = STATUS_USER_APC;
     return stack;
 }

[Paul Gofman]

On 1/8/21 20:29, Gabriel Ivăncescu wrote:
> Fixes a regression introduced by 175a3649ba04daaad3f2b5b62d6bfe091d6a9e46,
> which caused Winamp's in_wave module to crash when playing a wav file
> (the previous behavior only changed EAX when there was no context).
> Signed-off-by: Gabriel Ivăncescu
>
> dlls/ntdll/unix/signal_i386.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
>
> diff --git a/dlls/ntdll/unix/signal_i386.c b/dlls/ntdll/unix/signal_i386.c
> index ff9d8a1..f2d58dc 100644
> --- a/dlls/ntdll/unix/signal_i386.c
> +++ b/dlls/ntdll/unix/signal_i386.c
> @@ -1696,6 +1696,7 @@ struct apc_stack_layout * WINAPI setup_user_apc_dispatcher_stack( CONTEXT *conte
>      {
>          c.ContextFlags = CONTEXT_FULL;
>          NtGetContextThread( GetCurrentThread(), &c );
> -
>    c.Eax = STATUS_USER_APC;
>    context = &c;
> }
>    memmove( &stack->context, context, sizeof(stack->context) );
>
> @@ -1704,7 +1705,6 @@ struct apc_stack_layout * WINAPI setup_user_apc_dispatcher_stack( CONTEXT *conte
>      stack->arg1 = arg1;
>      stack->arg2 = arg2;
>      stack->func = func;
> - stack->context.Eax = STATUS_USER_APC;
> return stack;
>
> }

Thanks for spotting this. Are you planning to do the same for x64?

[Gabriel Ivăncescu]

I actually had no idea x64 had the same issue—I'll send a fix shortly, 
but I don't know of any apps to test it with (so if it's wrong, please 
resend corrected version).