[PATCH] riscv: jump_label: mark arguments as const to satisfy asm constraints

Jisheng Zhang
2022-10-06T06:50:17Z

Samuel reported that the static branch usage in cpu_relax() breaks
building with CONFIG_CC_OPTIMIZE_FOR_SIZE[1]:

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 in [2] "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.

[1]https://lore.kernel.org/linux-riscv/20220922060958.44203-1-samuel@sholland.org/
[2]https://lore.kernel.org/all/20210212094059.5f8d05e8@gandalf.local.home/
Signed-off-by: Jisheng Zhang <jszhang@kernel.org>
---
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