[PATCH] compiler_attributes.h: Support no_sanitize_undefined check with GCC 4

[Marco Elver <elver@google.com>]

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UBSAN is supported since GCC 4.9, which unfortunately did not yet have
__has_attribute(). To work around, the __GCC4_has_attribute workaround
requires defining which compiler version supports the given attribute.

In the case of no_sanitize_undefined, it is the first version that
supports UBSAN, which is GCC 4.9.

Reported-by: kernel test robot <lkp@intel.com>
Signed-off-by: Marco Elver <elver@google.com>
---

Doing a 'make W=1' with GCC 4.9 and the provided config fixes the build
robot's report.

Peter: Feel free to either squash this patch into the one adding
__no_sanitize_undefined or apply on top.

Although at this point we don't have any users of
__no_sanitize_undefined anymore since objtool resolved the noinstr
problem for UBSAN differently. We should probably keep the attribute
around because eventually somebody will need it.

Thanks,
-- Marco

---
 include/linux/compiler_attributes.h | 1 +
 1 file changed, 1 insertion(+)

diff --git a/include/linux/compiler_attributes.h b/include/linux/compiler_attributes.h
index cdf016596659..c8f03d2969df 100644
--- a/include/linux/compiler_attributes.h
+++ b/include/linux/compiler_attributes.h
@@ -40,6 +40,7 @@
 # define __GCC4_has_attribute___noclone__             1
 # define __GCC4_has_attribute___nonstring__           0
 # define __GCC4_has_attribute___no_sanitize_address__ (__GNUC_MINOR__ >= 8)
+# define __GCC4_has_attribute___no_sanitize_undefined__ (__GNUC_MINOR__ >= 9)
 # define __GCC4_has_attribute___fallthrough__         0
 #endif
 
-- 
2.27.0.290.gba653c62da-goog