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

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Message-ID: <Y0GBO77e2Lu/khkI@xhacker>
Date:   Sat, 8 Oct 2022 21:55:07 +0800
From:   Jisheng Zhang <jszhang@...nel.org>
To:     Conor.Dooley@...rochip.com
Cc:     peterz@...radead.org, jpoimboe@...nel.org, jbaron@...mai.com,
        rostedt@...dmis.org, ajones@...tanamicro.com, ardb@...nel.org,
        paul.walmsley@...ive.com, palmer@...belt.com,
        aou@...s.berkeley.edu, nathan@...nel.org, ndesaulniers@...gle.com,
        trix@...hat.com, samuel@...lland.org,
        linux-riscv@...ts.infradead.org, linux-kernel@...r.kernel.org,
        llvm@...ts.linux.dev
Subject: Re: [PATCH] riscv: jump_label: mark arguments as const to satisfy
 asm constraints

On Thu, Oct 06, 2022 at 12:44:32PM +0000, Conor.Dooley@...rochip.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@...nel.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@...tanamicro.com>
> > 
> > _______________________________________________
> > linux-riscv mailing list
> > linux-riscv@...ts.infradead.org
> > http://lists.infradead.org/mailman/listinfo/linux-riscv
> 

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