Re: [Qemu-devel] Qemu crashes on AAM 0

[malc]

On Sat, 28 Apr 2007, Joris van Rantwijk wrote:

> Qemu crashes with a floating point exception when emulating the "AAM 0"
> instruction. By "crash", I mean that the whole qemu process actually
> blows up (not just the program running inside Qemu).
>
> A real i386 machine would trigger a divide exception on AAM 0.
> This instruction form is undocumented of course, but blowing up the emulator
> seems a bit drastic. I'm willing to write/test/provide a patch to fix this,
> please let me know if that would be appreciated.
>
> To trigger this bug, I run the qemu-0.9.0 binary distribution for
> linux-i386 on Linux 2.6.21, without kqemu. I boot it with a FreeDOS
> floppy image, start DEBUG, assemble the instruction AAM 0, execute it, boom.
>
> By the way, Qemu is an amazing piece of work. I used it often and I'm quite
> impressed by its overal quality and stability.

Following (given that real iron does indeed produce divide by zero
exception) should do the trick.

Index: op.c
===================================================================
RCS file: /cvsroot/qemu/qemu/target-i386/op.c,v
retrieving revision 1.47
diff -u -r1.47 op.c
--- op.c        1 Feb 2007 22:11:07 -0000       1.47
+++ op.c        29 Apr 2007 15:54:47 -0000
@@ -1004,6 +1004,9 @@
 {
     int base = PARAM1;
     int al, ah;
+    if (!base) {
+        raise_exception(EXCP00_DIVZ);
+    }
     al = EAX & 0xff;
     ah = al / base;
     al = al % base;

--
vale