From: Josh Poimboeuf <jpoimboe@xxxxxxxxxx> Subject: bitops: always inline sign extension helpers With CONFIG_CC_OPTIMIZE_FOR_SIZE, objtool reports: drivers/gpu/drm/i915/gem/i915_gem_execbuffer.o: warning: objtool: i915_gem_execbuffer2_ioctl()+0x5b7: call to gen8_canonical_addr() with UACCESS enabled This means i915_gem_execbuffer2_ioctl() is calling gen8_canonical_addr() from the user_access_begin/end critical region (i.e, with SMAP disabled). While it's probably harmless in this case, in general we like to avoid extra function calls in SMAP-disabled regions because it can open up inadvertent security holes. Fix the warning by changing the sign extension helpers to __always_inline. This convinces GCC to inline gen8_canonical_addr(). The sign extension functions are trivial anyway, so it makes sense to always inline them. With my test optimize-for-size-based config, this actually shrinks the text size of i915_gem_execbuffer.o by 45 bytes -- and no change for vmlinux. Link: http://lkml.kernel.org/r/740179324b2b18b750b16295c48357f00b5fa9ed.1582982020.git.jpoimboe@xxxxxxxxxx Signed-off-by: Josh Poimboeuf <jpoimboe@xxxxxxxxxx> Reported-by: Randy Dunlap <rdunlap@xxxxxxxxxxxxx> Cc: Peter Zijlstra <peterz@xxxxxxxxxxxxx> Cc: Al Viro <viro@xxxxxxxxxxxxxxxxxx> Cc: Chris Wilson <chris@xxxxxxxxxxxxxxxxxx> Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx> --- include/linux/bitops.h | 4 ++-- 1 file changed, 2 insertions(+), 2 deletions(-) --- a/include/linux/bitops.h~bitops-always-inline-sign-extension-helpers +++ a/include/linux/bitops.h @@ -162,7 +162,7 @@ static inline __u8 ror8(__u8 word, unsig * * This is safe to use for 16- and 8-bit types as well. */ -static inline __s32 sign_extend32(__u32 value, int index) +static __always_inline __s32 sign_extend32(__u32 value, int index) { __u8 shift = 31 - index; return (__s32)(value << shift) >> shift; @@ -173,7 +173,7 @@ static inline __s32 sign_extend32(__u32 * @value: value to sign extend * @index: 0 based bit index (0<=index<64) to sign bit */ -static inline __s64 sign_extend64(__u64 value, int index) +static __always_inline __s64 sign_extend64(__u64 value, int index) { __u8 shift = 63 - index; return (__s64)(value << shift) >> shift; _
