[Xen-devel] [PATCH] x86emul: keep compiler from using {x, y, z}mm registers itself

["Jan Beulich" <JBeulich@xxxxxxxx>]

Since the emulator acts on the live hardware registers, we need to
prevent the compiler from using them e.g. for inlined memcpy() /
memset() (as gcc7 does). We can't, however, set this from the command
line, as otherwise the 64-bit build would face issues with functions
returning floating point values and being declared in standard headers.

As the pragma isn't available prior to gcc6, we need to invoke it
conditionally. Luckily up to gcc6 we haven't seen generated code access
SIMD registers beyond what our asm()s do.

Reported-by: George Dunlap <george.dunlap@xxxxxxxxxx>
Signed-off-by: Jan Beulich <jbeulich@xxxxxxxx>
---
While this doesn't affect core functionality, I think it would still be
nice for it to be allowed in for 4.10.

--- a/tools/tests/x86_emulator/x86-emulate.h
+++ b/tools/tests/x86_emulator/x86-emulate.h
@@ -4,6 +4,11 @@
 #include <stdint.h>
 #include <stdlib.h>
 #include <string.h>
+
+#if __GNUC__ >= 6
+#pragma GCC target("no-sse")
+#endif
+
 #include <xen/xen.h>
 
 #include <asm/msr-index.h>




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