[Qemu-devel] [5182] Fix up pxe boot (Glauber Costa)

[Anthony Liguori]

Revision: 5182
          http://svn.sv.gnu.org/viewvc/?view=rev&root=qemu&revision=5182
Author:   aliguori
Date:     2008-09-09 14:49:02 +0000 (Tue, 09 Sep 2008)

Log Message:
-----------
Fix up pxe boot (Glauber Costa)

As discussed in
http://lists.gnu.org/archive/html/qemu-devel/2008-08/msg00667.html,
current pxe boot is broken for some use cases. The problem
goes away if we reduce the number of allowed bits in the address space
to 32 (which has the side effect of reducing guest max mem size to 4Gb).

After digging for a while, it turns out that it happens because pxelinux
tries to access address 0x10009e9a6, which does not fit a 32-bit address.
A closer look, however, reveals this access is totally valid: It's just
0x9e9a6 with an add carry.

To avoid this, this patch casts the address passed to the POPL macro to
a 32-bit value. This is also done, although just theorectically, for
PUSHL too.

Signed-off-by: Glauber Costa <address@hidden>
Signed-off-by: Anthony Liguori <address@hidden>
Reported-by: Chris Lalancette <address@hidden>
CC: Eduardo Habkost <address@hidden>

Modified Paths:
--------------
    trunk/target-i386/op_helper.c

Modified: trunk/target-i386/op_helper.c
===================================================================
--- trunk/target-i386/op_helper.c       2008-09-07 21:00:01 UTC (rev 5181)
+++ trunk/target-i386/op_helper.c       2008-09-09 14:49:02 UTC (rev 5182)
@@ -590,6 +590,10 @@
 #define SET_ESP(val, sp_mask) ESP = (ESP & ~(sp_mask)) | ((val) & (sp_mask))
 #endif
 
+/* in 64-bit machines, this can overflow. So this segment addition macro
+ * can be used to trim the value to 32-bit whenever needed */
+#define SEG_ADDL(ssp, sp, sp_mask) ((uint32_t)((ssp) + (sp & (sp_mask))))
+
 /* XXX: add a is_user flag to have proper security support */
 #define PUSHW(ssp, sp, sp_mask, val)\
 {\
@@ -600,7 +604,7 @@
 #define PUSHL(ssp, sp, sp_mask, val)\
 {\
     sp -= 4;\
-    stl_kernel((ssp) + (sp & (sp_mask)), (val));\
+    stl_kernel(SEG_ADDL(ssp, sp, sp_mask), (uint32_t)(val));\
 }
 
 #define POPW(ssp, sp, sp_mask, val)\
@@ -611,7 +615,7 @@
 
 #define POPL(ssp, sp, sp_mask, val)\
 {\
-    val = (uint32_t)ldl_kernel((ssp) + (sp & (sp_mask)));\
+    val = (uint32_t)ldl_kernel(SEG_ADDL(ssp, sp, sp_mask));\
     sp += 4;\
 }