[PATCH] x86-paravirt: prevent gcc from generating the wrong addressingmode

[Jeremy Fitzhardinge]

When we generate a call sequence for calling a paravirtualized
function, we presume that the generated code is "call *0xXXXXX",
which is a 6 byte opcode; this is larger than a normal
direct call, and so we can patch a direct call over it.

At the moment, however we give gcc enough rope to hang us by
putting the address in a register and generating a two byte
indirect-via-register call.  Prevent this by explicitly
dereferencing the function pointer and passing it into the
asm as a constant.

This prevents crashes in VMI, as it cannot handle unpatchable
callsites.

Signed-off-by: Jeremy Fitzhardinge <jeremy.fitzhardinge@xxxxxxxxxx>
Cc: Alok Kataria <akataria@xxxxxxxxxx>

diff --git a/arch/x86/include/asm/paravirt.h b/arch/x86/include/asm/paravirt.h
index d4fec1f..6922d16 100644
--- a/arch/x86/include/asm/paravirt.h
+++ b/arch/x86/include/asm/paravirt.h
@@ -395,7 +395,7 @@ extern struct pv_lock_ops pv_lock_ops;

#define paravirt_type(op)				\
	[paravirt_typenum] "i" (PARAVIRT_PATCH(op)),	\
-	[paravirt_opptr] "m" (op)
+	[paravirt_opptr] "i" (&(op))
#define paravirt_clobber(clobber)		\
	[paravirt_clobber] "i" (clobber)

@@ -449,7 +449,7 @@ int paravirt_disable_iospace(void);
 * offset into the paravirt_patch_template structure, and can therefore be
 * freely converted back into a structure offset.
 */
-#define PARAVIRT_CALL	"call *%[paravirt_opptr];"
+#define PARAVIRT_CALL	"call *%c[paravirt_opptr];"

/*
 * These macros are intended to wrap calls through one of the paravirt


--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@xxxxxxxxxxxxxxx
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/