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objtool: Remove ANNOTATE_IGNORE_ALTERNATIVE from CLAC/STAC 

ANNOTATE_IGNORE_ALTERNATIVE adds additional noise to the code generated
by CLAC/STAC alternatives, hurting readability for those whose read
uaccess-related code generation on a regular basis.

Remove the annotation specifically for the "NOP patched with CLAC/STAC"
case in favor of a manual check.

Leave the other uses of that annotation in place as they're less common
and more difficult to detect.

Suggested-by: Linus Torvalds <torvalds@linux-foundation.org>
Signed-off-by: Josh Poimboeuf <jpoimboe@kernel.org>
Signed-off-by: Ingo Molnar <mingo@kernel.org>
Acked-by: Linus Torvalds <torvalds@linux-foundation.org>
Link: https://lore.kernel.org/r/fc972ba4995d826fcfb8d02733a14be8d670900b.1744098446.git.jpoimboe@kernel.org
This commit is contained in:
Josh Poimboeuf 2025-04-08 01:21:14 -07:00 committed by Ingo Molnar
parent 2dbbca9be4
commit 2d12c6fb78
2 changed files with 35 additions and 7 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

12
arch/x86/include/asm/smap.h
View File

@ -16,23 +16,23 @@
#ifdef __ASSEMBLER__
#define ASM_CLAC \
ALTERNATIVE __stringify(ANNOTATE_IGNORE_ALTERNATIVE), "clac", X86_FEATURE_SMAP
ALTERNATIVE "", "clac", X86_FEATURE_SMAP
#define ASM_STAC \
ALTERNATIVE __stringify(ANNOTATE_IGNORE_ALTERNATIVE), "stac", X86_FEATURE_SMAP
ALTERNATIVE "", "stac", X86_FEATURE_SMAP
#else /* __ASSEMBLER__ */
static __always_inline void clac(void)
{
/* Note: a barrier is implicit in alternative() */
alternative(ANNOTATE_IGNORE_ALTERNATIVE "", "clac", X86_FEATURE_SMAP);
alternative("", "clac", X86_FEATURE_SMAP);
}
static __always_inline void stac(void)
{
/* Note: a barrier is implicit in alternative() */
alternative(ANNOTATE_IGNORE_ALTERNATIVE "", "stac", X86_FEATURE_SMAP);
alternative("", "stac", X86_FEATURE_SMAP);
}
static __always_inline unsigned long smap_save(void)
@ -59,9 +59,9 @@ static __always_inline void smap_restore(unsigned long flags)
/* These macros can be used in asm() statements */
#define ASM_CLAC \
ALTERNATIVE(ANNOTATE_IGNORE_ALTERNATIVE "", "clac", X86_FEATURE_SMAP)
ALTERNATIVE("", "clac", X86_FEATURE_SMAP)
#define ASM_STAC \
ALTERNATIVE(ANNOTATE_IGNORE_ALTERNATIVE "", "stac", X86_FEATURE_SMAP)
ALTERNATIVE("", "stac", X86_FEATURE_SMAP)
#define ASM_CLAC_UNSAFE \
ALTERNATIVE("", ANNOTATE_IGNORE_ALTERNATIVE "clac", X86_FEATURE_SMAP)

30
tools/objtool/check.c
View File

@ -3505,6 +3505,34 @@ static struct instruction *next_insn_to_validate(struct objtool_file *file,
return next_insn_same_sec(file, alt_group->orig_group->last_insn);
}
static bool skip_alt_group(struct instruction *insn)
{
struct instruction *alt_insn = insn->alts ? insn->alts->insn : NULL;
/* ANNOTATE_IGNORE_ALTERNATIVE */
if (insn->alt_group && insn->alt_group->ignore)
return true;
/*
* For NOP patched with CLAC/STAC, only follow the latter to avoid
* impossible code paths combining patched CLAC with unpatched STAC
* or vice versa.
*
* ANNOTATE_IGNORE_ALTERNATIVE could have been used here, but Linus
* requested not to do that to avoid hurting .s file readability
* around CLAC/STAC alternative sites.
*/
if (!alt_insn)
return false;
/* Don't override ASM_{CLAC,STAC}_UNSAFE */
if (alt_insn->alt_group && alt_insn->alt_group->ignore)
return false;
return alt_insn->type == INSN_CLAC || alt_insn->type == INSN_STAC;
}
/*
* Follow the branch starting at the given instruction, and recursively follow
* any other branches (jumps). Meanwhile, track the frame pointer state at
@ -3625,7 +3653,7 @@ static int validate_branch(struct objtool_file *file, struct symbol *func,
}
}
if (insn->alt_group && insn->alt_group->ignore)
if (skip_alt_group(insn))
return 0;
if (handle_insn_ops(insn, next_insn, &state))