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

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Date:   Thu, 6 Oct 2022 12:44:32 +0000
From:   <Conor.Dooley@...rochip.com>
To:     <jszhang@...nel.org>
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 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,

Could you please make these normal link tags.?
Also could you please add the reported-by from samuel & a fixes tag?

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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