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s390/jump_label: Implement ARCH_STATIC_BRANCH_JUMP_ASM and ARCH_STATIC_BRANCH_ASM macros

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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>
This commit is contained in:
Jan Polensky
2026-06-01 19:46:21 +02:00
committed by Alexander Gordeev
parent 184b8dc879
commit 6900bec59d
1 changed files with 19 additions and 14 deletions
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33
arch/s390/include/asm/jump_label.h
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@@ -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 @@ static __always_inline bool arch_static_branch(struct static_key *key, bool bran
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;