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

Jisheng Zhang
2022-10-08T14:04:55Z

On Thu, Oct 06, 2022 at 12:44:32PM +0000, Conor.Dooley@microchip.com wrote:
> On 06/10/2022 13:41, Andrew Jones wrote:
> > EXTERNAL EMAIL: Do not click links or open attachments unless you know the content is safe
> >
> > On Thu, Oct 06, 2022 at 02:40:28PM +0800, Jisheng Zhang wrote:
> >> 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/
>
> Hey Jisheng,

Hi,

>
> Could you please make these normal link tags.?

How to make these link tags? I just used the permalink in
lore.kernel.org

> Also could you please add the reported-by from samuel & a fixes tag?

I will add Reported-by tag, but I'm not sure whether fixes tag
is suitable, and which commit I could use? commit 8eb060e1018
("arch/riscv: add Zihintpause support")?
>
> Thanks,
> Conor.
>
> >> 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
> >>
> >
> > Reviewed-by: Andrew Jones <ajones@ventanamicro.com>
> >
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>