Linux kernel mirror (for testing) git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git
kernel os linux

objtool, x86/hweight: Remove ANNOTATE_IGNORE_ALTERNATIVE

Since objtool's inception, frame pointer warnings have been manually
silenced for __arch_hweight*() to allow those functions' inline asm to
avoid using ASM_CALL_CONSTRAINT.

The potentially dubious reasoning for that decision over nine years ago
was that since !X86_FEATURE_POPCNT is exceedingly rare, it's not worth
hurting the code layout for a function call that will never happen on
the vast majority of systems.

However, those functions actually started using ASM_CALL_CONSTRAINT with
the following commit:

194a613088a8 ("x86/hweight: Use ASM_CALL_CONSTRAINT in inline asm()")

And rightfully so, as it makes the code correct. ASM_CALL_CONSTRAINT
will soon have no effect for non-FP configs anyway.

With ASM_CALL_CONSTRAINT in place, ANNOTATE_IGNORE_ALTERNATIVE no longer
has a purpose for the hweight functions. Remove it.

Signed-off-by: Josh Poimboeuf <jpoimboe@kernel.org>
Signed-off-by: Ingo Molnar <mingo@kernel.org>
Cc: Andy Lutomirski <luto@kernel.org>
Cc: Brian Gerst <brgerst@gmail.com>
Cc: H. Peter Anvin <hpa@zytor.com>
Cc: Juergen Gross <jgross@suse.com>
Cc: Kees Cook <keescook@chromium.org>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Link: https://lore.kernel.org/r/e7070dba3278c90f1a836b16157dcd34ccd21e21.1744318586.git.jpoimboe@kernel.org

authored by

Josh Poimboeuf and committed by
Ingo Molnar
7b3169df d51faee4

+2 -4
+2 -4
arch/x86/include/asm/arch_hweight.h
··· 16 16 { 17 17 unsigned int res; 18 18 19 - asm_inline (ALTERNATIVE(ANNOTATE_IGNORE_ALTERNATIVE 20 - "call __sw_hweight32", 19 + asm_inline (ALTERNATIVE("call __sw_hweight32", 21 20 "popcntl %[val], %[cnt]", X86_FEATURE_POPCNT) 22 21 : [cnt] "=" REG_OUT (res), ASM_CALL_CONSTRAINT 23 22 : [val] REG_IN (w)); ··· 45 46 { 46 47 unsigned long res; 47 48 48 - asm_inline (ALTERNATIVE(ANNOTATE_IGNORE_ALTERNATIVE 49 - "call __sw_hweight64", 49 + asm_inline (ALTERNATIVE("call __sw_hweight64", 50 50 "popcntq %[val], %[cnt]", X86_FEATURE_POPCNT) 51 51 : [cnt] "=" REG_OUT (res), ASM_CALL_CONSTRAINT 52 52 : [val] REG_IN (w));