linux-kernel - [PATCH -tip 0/3] x86/asm: Use generic asm operand modifiers instead of %P in asm templates

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Message-ID: <20240319104418.284519-1-ubizjak@gmail.com>
Date: Tue, 19 Mar 2024 11:40:11 +0100
From: Uros Bizjak <ubizjak@...il.com>
To: x86@...nel.org,
	linux-kernel@...r.kernel.org
Cc: Uros Bizjak <ubizjak@...il.com>,
	Andy Lutomirski <luto@...nel.org>,
	Brian Gerst <brgerst@...il.com>,
	Denys Vlasenko <dvlasenk@...hat.com>,
	"H . Peter Anvin" <hpa@...or.com>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	Ingo Molnar <mingo@...nel.org>,
	Josh Poimboeuf <jpoimboe@...hat.com>,
	Sean Christopherson <seanjc@...gle.com>
Subject: [PATCH -tip 0/3] x86/asm: Use generic asm operand modifiers instead of %P in asm templates

The "P" asm operand modifier is a x86 target-specific modifier.

For x86_64, when used with a symbol reference, the "P" modifier
emits "sym" instead of "sym(%rip)". When used with a constant, the
"P" modifier emits "cst" instead of "$cst". This property is used to
emit bare symbol references and bare constants without all
syntax-specific prefixes.

The generic "c", "n" and "a" operand modifiers should be used instead.
The following table shows the modifiers supported by all targets and
their effects:

Modifier    Description
-----------------------------------------------------------
'c'         Require a constant operand and print the
            constant expression with no punctuation.
'n'         Like '%c' except that the value of the constant
            is negated before printing.
'a'         Substitute a memory reference, with the actual
            operand treated as the address.  This may be
            useful when outputting a "load address"
            instruction, because often the assembler syntax
            for such an instruction requires you to write
            the operand as if it were a memory reference.

Also note that unlike GCC, clang emits %rip-relative symbol
reference with "P" asm operand modifier, so the patch also unifies
symbol handling with both compilers.

No functional changes intended.

Signed-off-by: Uros Bizjak <ubizjak@...il.com>
Cc: Andy Lutomirski <luto@...nel.org>
Cc: Brian Gerst <brgerst@...il.com>
Cc: Denys Vlasenko <dvlasenk@...hat.com>
Cc: H. Peter Anvin <hpa@...or.com>
Cc: Linus Torvalds <torvalds@...ux-foundation.org>
Cc: Ingo Molnar <mingo@...nel.org>
Cc: Josh Poimboeuf <jpoimboe@...hat.com>
Cc: Sean Christopherson <seanjc@...gle.com>

Uros Bizjak (3):
  x86/asm: Remove %P operand modifier from altinstr asm templates
  x86/asm: Use %c/%n instead of %P operand modifier in asm templates
  x86/asm: Use %a instead of %P operand modifier in asm templates

 arch/x86/boot/main.c                 |  4 ++--
 arch/x86/include/asm/alternative.h   | 22 +++++++++++-----------
 arch/x86/include/asm/apic.h          |  2 +-
 arch/x86/include/asm/atomic64_32.h   |  2 +-
 arch/x86/include/asm/cpufeature.h    |  4 ++--
 arch/x86/include/asm/irq_stack.h     |  2 +-
 arch/x86/include/asm/processor.h     |  6 +++---
 arch/x86/include/asm/special_insns.h |  4 ++--
 arch/x86/include/asm/uaccess.h       |  4 ++--
 9 files changed, 25 insertions(+), 25 deletions(-)

-- 
2.44.0