Anthony Liguori wrote:
Avi Kivity wrote:
Marcelo Tosatti wrote:
Some pvmmu functions store their commands on stack, and newer GCC
versions conclude that these commands are unused.
So stick an inline asm statement to convince the compiler otherwise.
Signed-off-by: Marcelo Tosatti <[EMAIL PROTECTED]>
diff --git a/arch/x86/kernel/kvm.c b/arch/x86/kernel/kvm.c
index 8b7a3cf..c892752 100644
--- a/arch/x86/kernel/kvm.c
+++ b/arch/x86/kernel/kvm.c
@@ -55,6 +55,12 @@ static void kvm_mmu_op(void *buffer, unsigned len)
int r;
unsigned long a1, a2;
+ /*
+ * GCC 4.3.0 concludes that on-stack kvm_mmu_op* is unused and
+ * optimizes its initialization away.
+ */
+ asm ("" : : "p" (buffer));
+
I don't think "p" should force the contents into memory? Perhaps
"m"(*(char *)buffer)?
Anthony, I don't see why a memory clobber would tell gcc that the
variables is actually used.
It doesn't, but it seems to me that it should force GCC to assume
everything is live. It's a big stick to hit the problem with but it
seems like the right thing semantically.
In general the right stick to hit a compiler with is 'volatile,' which
should tell the compiler that outside forces are in play. Without really
digging into the code I don't want to suggest just where this should be
used, but clearly Christian had the same thought.
The problem is with the void * -> unsigned long cast (__pa), once
that happens gcc loses track. It's probably needed anyway since
hypercalls _do_ clobber memory.
Right, it's not telling GCC that we touch a particular variable, but
rather that we may have touched any variable.
--
Bill Davidsen <[EMAIL PROTECTED]>
"We have more to fear from the bungling of the incompetent than from
the machinations of the wicked." - from Slashdot
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