[XEN] Fix i386 hypercall code to always create shadow

parameters. Arguments on stack can be clobbered by
callee, since it owns them. But we require this doesn't
happen when we create hypercall continuations. Hence the
need to copy.
Signed-off-by: Keir Fraser <keir@xensource.com>

diff --git a/xen/arch/x86/x86_32/entry.S b/xen/arch/x86/x86_32/entry.S
index 06a25fa188bc684dab730f814d1dbedf790f215b..7ec820c7b555ba52602dc2faf4ff9e27fc275acb 100644 (file)
--- a/xen/arch/x86/x86_32/entry.S
+++ b/xen/arch/x86/x86_32/entry.S
@@ -175,7 +175,7 @@ ENTRY(hypercall)
         jae   bad_hypercall
         PERFC_INCR(PERFC_hypercalls, %eax)
 #ifndef NDEBUG
-        /* Deliberately corrupt parameter regs not used by this hypercall. */
+        /* Create shadow parameters and corrupt those not used by this call. */
         pushl %eax
         pushl UREGS_eip+4(%esp)
         pushl 28(%esp) # EBP
@@ -192,11 +192,23 @@ ENTRY(hypercall)
         movl  $0xDEADBEEF,%eax
         rep   stosl
         movl  %esi,%eax
+#else
+        /* 
+         * We need shadow parameters even on non-debug builds. We depend on the
+         * original versions not being clobbered (needed to create a hypercall
+         * continuation). But that isn't guaranteed by the function-call ABI.
+         */ 
+        pushl 20(%esp) # EBP
+        pushl 20(%esp) # EDI
+        pushl 20(%esp) # ESI
+        pushl 20(%esp) # EDX
+        pushl 20(%esp) # ECX
+        pushl 20(%esp) # EBX
 #endif
         call *hypercall_table(,%eax,4)
+        addl  $24,%esp     # Discard the shadow parameters
 #ifndef NDEBUG
-        /* Deliberately corrupt parameter regs used by this hypercall. */
-        addl  $24,%esp     # Shadow parameters
+        /* Deliberately corrupt real parameter regs used by this hypercall. */
         popl  %ecx         # Shadow EIP
         cmpl  %ecx,UREGS_eip+4(%esp)
         popl  %ecx         # Shadow hypercall index