From: Jan Polensky <japo@linux.ibm.com>
Date: Mon, 1 Jun 2026 17:46:21 +0000 (+0200)
Subject: s390/jump_label: Implement ARCH_STATIC_BRANCH_JUMP_ASM and ARCH_STATIC_BRANCH_ASM... 
X-Git-Url: http://git.ipfire.org/cgi-bin/gitweb.cgi?a=commitdiff_plain;h=6900bec59d0f54dbb94d0799d204bcd44fbdb623;p=thirdparty%2Flinux.git

s390/jump_label: Implement ARCH_STATIC_BRANCH_JUMP_ASM and ARCH_STATIC_BRANCH_ASM macros

Rust static branch support needs the s390 jump label instruction sequence
and __jump_table emission in a reusable form. The current implementation
embeds the sequence directly in the C asm goto blocks, which cannot be
shared with Rust.

Introduce ARCH_STATIC_BRANCH_ASM and ARCH_STATIC_BRANCH_JUMP_ASM to
describe the brcl sequences for the likely-false and likely-true cases
and to emit the same __jump_table entries as before. Switch the existing
C helpers to use the new macros to avoid duplication without changing
the generated code.

Acked-by: Gary Guo <gary@garyguo.net>
Acked-by: Miguel Ojeda <ojeda@kernel.org>
Acked-by: Heiko Carstens <hca@linux.ibm.com>
Reviewed-by: Alice Ryhl <aliceryhl@google.com>
Signed-off-by: Jan Polensky <japo@linux.ibm.com>
Signed-off-by: Alexander Gordeev <agordeev@linux.ibm.com>
---

diff --git a/arch/s390/include/asm/jump_label.h b/arch/s390/include/asm/jump_label.h
index d9cbc18f6b2ee..0e28c90dc2425 100644
--- a/arch/s390/include/asm/jump_label.h
+++ b/arch/s390/include/asm/jump_label.h
@@ -19,19 +19,29 @@
 #define JUMP_LABEL_STATIC_KEY_CONSTRAINT "jdd"
 #endif
 
+#define ARCH_JUMP_TABLE_ENTRY(key, label, local_label)	\
+	".pushsection __jump_table,\"aw\"\n"		\
+	".balign	8\n"				\
+	".long	" local_label "-.," label "-.\n"	\
+	".quad	" key "-.\n"				\
+	".popsection\n"
+
 /*
  * We use a brcl 0,<offset> instruction for jump labels so it
  * can be easily distinguished from a hotpatch generated instruction.
  */
+#define ARCH_STATIC_BRANCH_ASM(key, label)	\
+	"0:	brcl 0," label "\n"		\
+	ARCH_JUMP_TABLE_ENTRY(key, label, "0b")
+
+#define ARCH_STATIC_BRANCH_JUMP_ASM(key, label)	\
+	"0:	brcl 15," label "\n"		\
+	ARCH_JUMP_TABLE_ENTRY(key, label, "0b")
+
 static __always_inline bool arch_static_branch(struct static_key *key, bool branch)
 {
-	asm goto("0:	brcl 0,%l[label]\n"
-			  ".pushsection __jump_table,\"aw\"\n"
-			  ".balign	8\n"
-			  ".long	0b-.,%l[label]-.\n"
-			  ".quad	%0+%1-.\n"
-			  ".popsection\n"
-			  : : JUMP_LABEL_STATIC_KEY_CONSTRAINT (key), "i" (branch) : : label);
+	asm goto(ARCH_STATIC_BRANCH_ASM("%0+%1", "%l[label]")
+		: : JUMP_LABEL_STATIC_KEY_CONSTRAINT (key), "i" (branch) : : label);
 	return false;
 label:
 	return true;
@@ -39,13 +49,8 @@ label:
 
 static __always_inline bool arch_static_branch_jump(struct static_key *key, bool branch)
 {
-	asm goto("0:	brcl 15,%l[label]\n"
-			  ".pushsection __jump_table,\"aw\"\n"
-			  ".balign	8\n"
-			  ".long	0b-.,%l[label]-.\n"
-			  ".quad	%0+%1-.\n"
-			  ".popsection\n"
-			  : : JUMP_LABEL_STATIC_KEY_CONSTRAINT (key), "i" (branch) : : label);
+	asm goto(ARCH_STATIC_BRANCH_JUMP_ASM("%0+%1", "%l[label]")
+		: : JUMP_LABEL_STATIC_KEY_CONSTRAINT (key), "i" (branch) : : label);
 	return false;
 label:
 	return true;