linux-kernel - [PATCH 0/8] objtool, x86/alternative: Convert objtool annotations and x86 alternatives to assembler macros

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Message-ID: <cover.1765044697.git.jpoimboe@kernel.org>
Date: Sat,  6 Dec 2025 13:41:07 -0800
From: Josh Poimboeuf <jpoimboe@...nel.org>
To: x86@...nel.org
Cc: linux-kernel@...r.kernel.org,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	Ingo Molnar <mingo@...nel.org>,
	Peter Zijlstra <peterz@...radead.org>,
	Borislav Petkov <bp@...en8.de>,
	Thomas Gleixner <tglx@...utronix.de>
Subject: [PATCH 0/8] objtool, x86/alternative: Convert objtool annotations and x86 alternatives to assembler macros

Convert objtool annotations and x86 alternatives to assembler macros.
This creates a shared C/asm alternative implementation and makes the
code generation significantly more readable.

Patches 1-5: convert objtool
Patches 6-8: convert alternatives

Based on tip/master.

Before:
-----
  # ./arch/x86/include/asm/smap.h:47: 	alternative("", "stac", X86_FEATURE_SMAP);
  # 47 "./arch/x86/include/asm/smap.h" 1
  	# ALT: oldinstr
  771:

  772:
  # ALT: padding
  .skip -(((775f-774f)-(772b-771b)) > 0) * ((775f-774f)-(772b-771b)),0x90
  773:
  .pushsection .altinstructions, "aM", @progbits, 14
   .long 771b - .
   .long 774f - .
   .4byte ( 9*32+20)
   .byte 773b-771b
   .byte 775f-774f
  .popsection
  .pushsection .altinstr_replacement, "ax"
  .pushsection .discard.annotate_data, "M", @progbits, 8; .long 1b - ., 1; .popsection
  # ALT: replacement
  774:
  	stac
  775:
  .popsection
-----

After:
-----
  # ./arch/x86/include/asm/smap.h:47: 	alternative("", "stac", X86_FEATURE_SMAP);
  # 47 "./arch/x86/include/asm/smap.h" 1
	ALTERNATIVE "", "stac", "( 9*32+20)"
-----

Future work:
  - BUG()/WARN()
  - static_cpu_has()
  - static calls/branches
  - exceptions
  - smp locks
  - unwind hints

Josh Poimboeuf (8):
  objtool: Rename ANNOTYPE_IGNORE_ALTS -> ANNOTYPE_IGNORE_ALTERNATIVE
  objtool: Make ANNOTYPE_DATA_SPECIAL unique across all annotations
  objtool: Rename C ANNOTATE_REACHABLE to ANNOTATE_REACHABLE_LABEL
  objtool: Rename asm ANNOTATE_NOCFI_SYM to ANNOTATE_NOCFI
  objtool: Convert annotations to assembler macros
  x86/asm: Use unique code labels in __FILL_RETURN_BUFFER
  x86/asm: Remove newlines in alternatives
  x86/alternative: Convert alternatives to assembler macros

 arch/x86/include/asm/alternative.h    | 196 +++++++++++++-------------
 arch/x86/include/asm/asm.h            |   8 +-
 arch/x86/include/asm/bug.h            |   2 +-
 arch/x86/include/asm/irq_stack.h      |   2 +-
 arch/x86/include/asm/jump_label.h     |   1 +
 arch/x86/include/asm/nospec-branch.h  |   8 +-
 arch/x86/include/asm/paravirt_types.h |   2 +-
 arch/x86/include/asm/processor.h      |   2 +-
 arch/x86/include/asm/smap.h           |   8 +-
 arch/x86/include/asm/vmware.h         |   2 +-
 arch/x86/platform/efi/efi_stub_64.S   |   2 +-
 include/linux/annotate.h              | 133 ++++++++---------
 include/linux/objtool_types.h         |   5 +-
 tools/include/linux/objtool_types.h   |   5 +-
 tools/objtool/check.c                 |   4 +-
 15 files changed, 196 insertions(+), 184 deletions(-)

-- 
2.52.0