linux-kernel - Re: [PATCH v10 5/5] rust: add arch_static

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Message-ID: <20241011152312.r5sy7k7hsunmmbfo@treble>
Date: Fri, 11 Oct 2024 08:23:12 -0700
From: Josh Poimboeuf <jpoimboe@...nel.org>
To: Alice Ryhl <aliceryhl@...gle.com>
Cc: Steven Rostedt <rostedt@...dmis.org>,
	Masami Hiramatsu <mhiramat@...nel.org>,
	Mathieu Desnoyers <mathieu.desnoyers@...icios.com>,
	Peter Zijlstra <peterz@...radead.org>,
	Jason Baron <jbaron@...mai.com>, Ard Biesheuvel <ardb@...nel.org>,
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	Alex Gaynor <alex.gaynor@...il.com>,
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	Björn Roy Baron <bjorn3_gh@...tonmail.com>,
	Benno Lossin <benno.lossin@...ton.me>,
	Andreas Hindborg <a.hindborg@...nel.org>,
	linux-trace-kernel@...r.kernel.org, rust-for-linux@...r.kernel.org,
	linux-kernel@...r.kernel.org, Arnd Bergmann <arnd@...db.de>,
	linux-arch@...r.kernel.org, Thomas Gleixner <tglx@...utronix.de>,
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	linux-arm-kernel@...ts.infradead.org,
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	Palmer Dabbelt <palmer@...belt.com>,
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	linux-riscv@...ts.infradead.org,
	Huacai Chen <chenhuacai@...nel.org>,
	WANG Xuerui <kernel@...0n.name>, Bibo Mao <maobibo@...ngson.cn>,
	Tiezhu Yang <yangtiezhu@...ngson.cn>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Tianrui Zhao <zhaotianrui@...ngson.cn>, loongarch@...ts.linux.dev
Subject: Re: [PATCH v10 5/5] rust: add arch_static_branch

On Fri, Oct 11, 2024 at 10:13:38AM +0000, Alice Ryhl wrote:
> +#[cfg(CONFIG_JUMP_LABEL)]
> +#[cfg(not(CONFIG_HAVE_JUMP_LABEL_HACK))]
> +macro_rules! arch_static_branch {
> +    ($key:path, $keytyp:ty, $field:ident, $branch:expr) => {'my_label: {
> +        $crate::asm!(
> +            include!(concat!(env!("OBJTREE"), "/rust/kernel/arch_static_branch_asm.rs"));
> +            l_yes = label {
> +                break 'my_label true;
> +            },
> +            symb = sym $key,
> +            off = const ::core::mem::offset_of!($keytyp, $field),
> +            branch = const $crate::jump_label::bool_to_int($branch),
> +        );
> +
> +        break 'my_label false;
> +    }};
> +}
> +
> +#[macro_export]
> +#[doc(hidden)]
> +#[cfg(CONFIG_JUMP_LABEL)]
> +#[cfg(CONFIG_HAVE_JUMP_LABEL_HACK)]
> +macro_rules! arch_static_branch {
> +    ($key:path, $keytyp:ty, $field:ident, $branch:expr) => {'my_label: {
> +        $crate::asm!(
> +            include!(concat!(env!("OBJTREE"), "/rust/kernel/arch_static_branch_asm.rs"));
> +            l_yes = label {
> +                break 'my_label true;
> +            },
> +            symb = sym $key,
> +            off = const ::core::mem::offset_of!($keytyp, $field),
> +            branch = const 2 | $crate::jump_label::bool_to_int($branch),
> +        );
> +
> +        break 'my_label false;
> +    }};

Ouch... could we get rid of all this duplication by containing the hack
bit to ARCH_STATIC_BRANCH_ASM() like so?

diff --git a/arch/x86/include/asm/jump_label.h b/arch/x86/include/asm/jump_label.h
index ffd0d1a1a4af..3f1c1d6c0da1 100644
--- a/arch/x86/include/asm/jump_label.h
+++ b/arch/x86/include/asm/jump_label.h
@@ -24,7 +24,7 @@
 #ifdef CONFIG_HAVE_JUMP_LABEL_HACK
 #define ARCH_STATIC_BRANCH_ASM(key, label)		\
 	"1: jmp " label " # objtool NOPs this \n\t"	\
-	JUMP_TABLE_ENTRY(key, label)
+	JUMP_TABLE_ENTRY(key " + 2", label)
 #else /* !CONFIG_HAVE_JUMP_LABEL_HACK */
 #define ARCH_STATIC_BRANCH_ASM(key, label)		\
 	"1: .byte " __stringify(BYTES_NOP5) "\n\t"	\
@@ -33,10 +33,8 @@
 
 static __always_inline bool arch_static_branch(struct static_key * const key, const bool branch)
 {
-	int hack_bit = IS_ENABLED(CONFIG_HAVE_JUMP_LABEL_HACK) ? 2 : 0;
-
 	asm goto(ARCH_STATIC_BRANCH_ASM("%c0 + %c1", "%l[l_yes]")
-		: :  "i" (key), "i" (hack_bit | branch) : : l_yes);
+		: :  "i" (key), "i" (branch) : : l_yes);
 
 	return false;
 l_yes: