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Message-ID: <Yz6V2Ffm5jSJJa1V@xhacker>
Date: Thu, 6 Oct 2022 16:46:16 +0800
From: Jisheng Zhang <jszhang@...nel.org>
To: Ard Biesheuvel <ardb@...nel.org>
Cc: Catalin Marinas <catalin.marinas@....com>,
Will Deacon <will@...nel.org>,
Peter Zijlstra <peterz@...radead.org>,
Josh Poimboeuf <jpoimboe@...nel.org>,
Jason Baron <jbaron@...mai.com>,
Steven Rostedt <rostedt@...dmis.org>,
Mark Rutland <mark.rutland@....com>,
linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 1/2] arm64: jump_label: mark arguments as const to
satisfy asm constraints
On Thu, Oct 06, 2022 at 10:17:44AM +0200, Ard Biesheuvel wrote:
> On Thu, 6 Oct 2022 at 10:05, Jisheng Zhang <jszhang@...nel.org> wrote:
> >
> > Inspired by x86 commit 864b435514b2("x86/jump_label: Mark arguments as
> > const to satisfy asm constraints"), mark arch_static_branch()'s and
> > arch_static_branch_jump()'s arguments as const to satisfy asm
> > constraints. And Steven in [1] also pointed out that "The "i"
> > constraint needs to be a constant."
> >
> > Tested with building a simple external kernel module with "O0".
> >
> > [1]https://lore.kernel.org/all/20210212094059.5f8d05e8@gandalf.local.home/
> >
> > Signed-off-by: Jisheng Zhang <jszhang@...nel.org>
> > ---
> > arch/arm64/include/asm/jump_label.h | 8 ++++----
> > 1 file changed, 4 insertions(+), 4 deletions(-)
> >
> > diff --git a/arch/arm64/include/asm/jump_label.h b/arch/arm64/include/asm/jump_label.h
> > index cea441b6aa5d..48ddc0f45d22 100644
> > --- a/arch/arm64/include/asm/jump_label.h
> > +++ b/arch/arm64/include/asm/jump_label.h
> > @@ -15,8 +15,8 @@
> >
> > #define JUMP_LABEL_NOP_SIZE AARCH64_INSN_SIZE
> >
> > -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(
> > "1: nop \n\t"
>
> Is this still necessary if we specify the constraints in a more
> reasonable manner:
>
> " .quad %c0 - . + %1 \n\t"
> : : "i"(key), "i"(branch) : : l_yes);
Just tried this locally with the simple external kernel module, the
asm operand 0 probably does not match constraints can still be
reproduced with "O0".
Thanks
>
> instead of the horrid hack with the char* cast and using a bool as an
> array index?
>
>
>
>
> > @@ -32,8 +32,8 @@ 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(
> > "1: b %l[l_yes] \n\t"
> > --
> > 2.37.2
> >
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