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

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Date:   Tue, 1 Nov 2022 01:49:01 +0800
From:   Jisheng Zhang <jszhang@...nel.org>
To:     Conor Dooley <conor.dooley@...rochip.com>
Cc:     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>, 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: Re: [PATCH v2] riscv: jump_label: mark arguments as const to satisfy
 asm constraints

On Wed, Oct 12, 2022 at 02:28:16PM +0100, Conor Dooley wrote:
> Hey Jisheng,

Hi Conor,

> LKP reported an error that seems to only have gone to myself & Samuel,
> but the branch it's complaining about is your v1:
> https://lore.kernel.org/lkml/202210122123.Cc4FPShJ-lkp@intel.com/
> 
> Any idea what the story is here?

I tried the config in the link, I can reproduce the build error w/
and w/o the my patch. So I think the root cause of the build error
is a different story. I have a fix in local repo, will send it out
soon.

Thanks

> 
> Thanks,
> Conor.
> 
> On Sat, Oct 08, 2022 at 10:54:37PM +0800, Jisheng Zhang wrote:
> > 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
> >