Re: [Qemu-devel] Crash due to invalid env->current_tb

[Adam Lackorzynski <adam@os.inf.tu-dresden.de>]

On Wed Apr 30, 2008 at 17:11:32 +0200, Adam Lackorzynski wrote:
> On Wed Apr 30, 2008 at 11:08:46 +0200, Alexander Graf wrote:
> > There was a comment from Fabrice on how to do prologues in TCG to save / 
> > restore the clobbered values. Btw, ebx gets clobbered as well.
> 
> tcg/README says that some registers are clobbered. So something like
> this should be safe:
> 
> Index: cpu-exec.c
> ===================================================================
> --- cpu-exec.c	(revision 4276)
> +++ cpu-exec.c	(working copy)
> @@ -690,6 +691,15 @@
>  		fp.ip = tc_ptr;
>  		fp.gp = code_gen_buffer + 2 * (1 << 20);
>  		(*(void (*)(void)) &fp)();
> +#elif defined(__i386)
> +		asm volatile ("push %%ebp\n"
> +		              "push %%ebx\n"
> +		              "call *%1\n"
> +			      "pop %%ebx\n"
> +			      "pop %%ebp\n"
> +		              : "=a" (T0)
> +			      : "r" (gen_func)
> +			      : "esi", "edi", "ecx", "edx");
>  #else
>                  T0 = gen_func();
>  #endif

I just realised that the push and pop of ebx is not needed as T0 is ebx
which gets overwritten in the output anyway.

Index: cpu-exec.c
===================================================================
--- cpu-exec.c	(revision 4276)
+++ cpu-exec.c	(working copy)
@@ -690,6 +691,13 @@
 		fp.ip = tc_ptr;
 		fp.gp = code_gen_buffer + 2 * (1 << 20);
 		(*(void (*)(void)) &fp)();
+#elif defined(__i386)
+		asm volatile ("push %%ebp\n"
+		              "call *%1\n"
+			      "pop %%ebp\n"
+		              : "=a" (T0)
+			      : "r" (gen_func)
+			      : "esi", "edi", "ecx", "edx");
 #else
                 T0 = gen_func();
 #endif


Adam
-- 
Adam                 adam@os.inf.tu-dresden.de
  Lackorzynski         http://os.inf.tu-dresden.de/~adam/