[RFC PATCH v2 4/7] riscv/runtime-const: Introduce runtime_const_mask_32()
From: K Prateek Nayak <kprateek.nayak@amd.com>
Date: 2026-03-16 05:25:46
Also in:
linux-arch, linux-riscv, linux-s390, lkml
Subsystem:
risc-v architecture, the rest · Maintainers:
Paul Walmsley, Palmer Dabbelt, Albert Ou, Linus Torvalds
Futex hash computation requires a mask operation with read-only after init data that will be converted to a runtime constant in the subsequent commit. Introduce runtime_const_mask_32 to further optimize the mask operation in the futex hash computation hot path. GCC generates a: lui a0, 0x12346 # upper; +0x800 then >>12 for correct rounding addi a0, a0, 0x678 # lower 12 bits and a1, a1, a0 # a1 = a1 & a0 pattern to tackle arbitrary 32-bit masks and the same was also suggested by Claude which is implemented here. __runtime_fixup_ptr() already patches a "lui + addi" sequence which has been reused to patch the same sequence for __runtime_fixup_mask(). Assisted-by: Claude:claude-sonnet-4-5 Signed-off-by: K Prateek Nayak <kprateek.nayak@amd.com> --- arch/riscv/include/asm/runtime-const.h | 24 ++++++++++++++++++++++++ 1 file changed, 24 insertions(+)
diff --git a/arch/riscv/include/asm/runtime-const.h b/arch/riscv/include/asm/runtime-const.h
index d766e2b9e6df..f54289a7ddeb 100644
--- a/arch/riscv/include/asm/runtime-const.h
+++ b/arch/riscv/include/asm/runtime-const.h@@ -153,6 +153,24 @@ __ret; \ }) +#define runtime_const_mask_32(val, sym) \ +({ \ + u32 __ret; \ + asm_inline(".option push\n\t" \ + ".option norvc\n\t" \ + "1:\t" \ + "lui %[__ret],0x89abd\n\t" \ + "addi %[__ret],%[__ret],-0x211\n\t" \ + "and %[__ret],%[__ret],%[__val]\n\t" \ + ".option pop\n\t" \ + ".pushsection runtime_mask_" #sym ",\"a\"\n\t" \ + ".long 1b - .\n\t" \ + ".popsection" \ + : [__ret] "=&r" (__ret) \ + : [__val] "r" (val)); \ + __ret; \ +}) + #define runtime_const_init(type, sym) do { \ extern s32 __start_runtime_##type##_##sym[]; \ extern s32 __stop_runtime_##type##_##sym[]; \
@@ -256,6 +274,12 @@ static inline void __runtime_fixup_shift(void *where, unsigned long val) mutex_unlock(&text_mutex); } +static inline void __runtime_fixup_mask(void *where, unsigned long val) +{ + __runtime_fixup_32(where, where + 4, val); + __runtime_fixup_caches(where, 2); +} + static inline void runtime_const_fixup(void (*fn)(void *, unsigned long), unsigned long val, s32 *start, s32 *end) {
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2.43.0