Re: [PATCH v10 5/5] rust: add arch_static_branch

[Josh Poimboeuf <jpoimboe@kernel.org>]

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: