linux-kernel - [PATCH v2] riscv: jump_label: mark arguments as const to satisfy asm constraints

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Message-Id: <20221008145437.491-1-jszhang@kernel.org>
Date:   Sat,  8 Oct 2022 22:54:37 +0800
From:   Jisheng Zhang <jszhang@...nel.org>
To:     Peter Zijlstra <peterz@...radead.org>,
        Josh Poimboeuf <jpoimboe@...nel.org>,
        Jason Baron <jbaron@...mai.com>,
        Steven Rostedt <rostedt@...dmis.org>,
        Ard Biesheuvel <ardb@...nel.org>,
        Paul Walmsley <paul.walmsley@...ive.com>,
        Palmer Dabbelt <palmer@...belt.com>,
        Albert Ou <aou@...s.berkeley.edu>,
        Nathan Chancellor <nathan@...nel.org>,
        Nick Desaulniers <ndesaulniers@...gle.com>,
        Tom Rix <trix@...hat.com>
Cc:     linux-riscv@...ts.infradead.org, linux-kernel@...r.kernel.org,
        llvm@...ts.linux.dev, Samuel Holland <samuel@...lland.org>,
        Andrew Jones <ajones@...tanamicro.com>
Subject: [PATCH v2] riscv: jump_label: mark arguments as const to satisfy asm constraints

Samuel reported that the static branch usage in cpu_relax() breaks
building with CONFIG_CC_OPTIMIZE_FOR_SIZE:

In file included from <command-line>:
./arch/riscv/include/asm/jump_label.h: In function 'cpu_relax':
././include/linux/compiler_types.h:285:33: warning: 'asm' operand 0
probably does not match constraints
  285 | #define asm_volatile_goto(x...) asm goto(x)
      |                                 ^~~
./arch/riscv/include/asm/jump_label.h:41:9: note: in expansion of macro
'asm_volatile_goto'
   41 |         asm_volatile_goto(
      |         ^~~~~~~~~~~~~~~~~
././include/linux/compiler_types.h:285:33: error: impossible constraint
in 'asm'
  285 | #define asm_volatile_goto(x...) asm goto(x)
      |                                 ^~~
./arch/riscv/include/asm/jump_label.h:41:9: note: in expansion of macro
'asm_volatile_goto'
   41 |         asm_volatile_goto(
      |         ^~~~~~~~~~~~~~~~~
make[1]: *** [scripts/Makefile.build:249:
arch/riscv/kernel/vdso/vgettimeofday.o] Error 1
make: *** [arch/riscv/Makefile:128: vdso_prepare] Error 2

Maybe "-Os" prevents GCC from detecting that the key/branch arguments
can be treated as constants and used as immediate operands. Inspired
by x86's commit 864b435514b2("x86/jump_label: Mark arguments as const to
satisfy asm constraints"), and as pointed out by Steven: "The "i"
constraint needs to be a constant.", let's do similar modifications to
riscv.

Tested by CC_OPTIMIZE_FOR_SIZE + gcc and CC_OPTIMIZE_FOR_SIZE + clang.

Link: https://lore.kernel.org/linux-riscv/20220922060958.44203-1-samuel@sholland.org/
Link: https://lore.kernel.org/all/20210212094059.5f8d05e8@gandalf.local.home/
Fixes: 8eb060e10185 ("arch/riscv: add Zihintpause support")
Reported-by: Samuel Holland <samuel@...lland.org>
Signed-off-by: Jisheng Zhang <jszhang@...nel.org>
Reviewed-by: Andrew Jones <ajones@...tanamicro.com>
---

since v1:
 - add Reported-by, Reviewed-by, Fixes and Link tag

 arch/riscv/include/asm/jump_label.h | 8 ++++----
 1 file changed, 4 insertions(+), 4 deletions(-)

diff --git a/arch/riscv/include/asm/jump_label.h b/arch/riscv/include/asm/jump_label.h
index 38af2ec7b9bf..6d58bbb5da46 100644
--- a/arch/riscv/include/asm/jump_label.h
+++ b/arch/riscv/include/asm/jump_label.h
@@ -14,8 +14,8 @@
 
 #define JUMP_LABEL_NOP_SIZE 4
 
-static __always_inline bool arch_static_branch(struct static_key *key,
-					       bool branch)
+static __always_inline bool arch_static_branch(struct static_key * const key,
+					       const bool branch)
 {
 	asm_volatile_goto(
 		"	.option push				\n\t"
@@ -35,8 +35,8 @@ static __always_inline bool arch_static_branch(struct static_key *key,
 	return true;
 }
 
-static __always_inline bool arch_static_branch_jump(struct static_key *key,
-						    bool branch)
+static __always_inline bool arch_static_branch_jump(struct static_key * const key,
+						    const bool branch)
 {
 	asm_volatile_goto(
 		"	.option push				\n\t"
-- 
2.37.2