From: Jisheng Zhang <jszhang@kernel.org>
To: Ard Biesheuvel <ardb@kernel.org>
Cc: Catalin Marinas <catalin.marinas@arm.com>,
Will Deacon <will@kernel.org>,
Peter Zijlstra <peterz@infradead.org>,
Josh Poimboeuf <jpoimboe@kernel.org>,
Jason Baron <jbaron@akamai.com>,
Steven Rostedt <rostedt@goodmis.org>,
Mark Rutland <mark.rutland@arm.com>,
linux-arm-kernel@lists.infradead.org,
linux-kernel@vger.kernel.org
Subject: Re: [PATCH 1/2] arm64: jump_label: mark arguments as const to satisfy asm constraints
Date: Thu, 6 Oct 2022 19:04:25 +0800 [thread overview]
Message-ID: <Yz62Oa+GmDeC2yYm@xhacker> (raw)
In-Reply-To: <CAMj1kXEdq+9BdFSD0CRgBVef9PJ=tAbhkRzkKz87CYomigr59Q@mail.gmail.com>
On Thu, Oct 06, 2022 at 11:08:32AM +0200, Ard Biesheuvel wrote:
> On Thu, 6 Oct 2022 at 10:55, Jisheng Zhang <jszhang@kernel.org> wrote:
> >
> > On Thu, Oct 06, 2022 at 10:17:44AM +0200, Ard Biesheuvel wrote:
> > > On Thu, 6 Oct 2022 at 10:05, Jisheng Zhang <jszhang@kernel.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@kernel.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".
> >
>
> OK so the key pointer needs to be pointer-to-const, which makes sense.
> How about when using "Si" as the constraint for operand 0?
"Si" constraint doesn't help either.
>
>
> >
> > >
> > > 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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next prev parent reply other threads:[~2022-10-06 11:15 UTC|newest]
Thread overview: 11+ messages / expand[flat|nested] mbox.gz Atom feed top
2022-10-06 7:55 [PATCH 0/2] arm64: constify arguments to satisfy asm constraints Jisheng Zhang
2022-10-06 7:55 ` [PATCH 1/2] arm64: jump_label: mark arguments as const " Jisheng Zhang
2022-10-06 8:17 ` Ard Biesheuvel
2022-10-06 8:46 ` Jisheng Zhang
2022-10-06 8:55 ` Jisheng Zhang
2022-10-06 9:08 ` Ard Biesheuvel
2022-10-06 11:04 ` Jisheng Zhang [this message]
2022-10-06 10:14 ` Mark Rutland
2022-10-06 11:53 ` Jisheng Zhang
2022-10-06 7:55 ` [PATCH 2/2] arm64: alternative: constify alternative_has_feature_* argument Jisheng Zhang
2022-11-07 19:08 ` [PATCH 0/2] arm64: constify arguments to satisfy asm constraints Will Deacon
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