On Mon, 18 May 2026 15:14:06 +0200 Milan Tripkovic <[email protected]> wrote:
> From: Milan Tripkovic <[email protected]> > > Add an assembly implementation of memcmp() for RISC-V. The implementation > uses the ZBB extension for word-at-a-time comparison and an assembly > fallback for non-ZBB systems. I think I mentioned before that the only ZBB bit I can see is the byte reverse at the end needed to get the correct sign. For non-ZBB it would be better to fall back to a byte compare at that point. Oh - and there should be change info for this patch in this email. -- David > > Benchmark results (QEMU TCG, rv64, Aligned): > > Len | Default | NoZBB | ZBB | %NoZBB | %ZBB > ------|---------|--------|--------|--------|------- > 1 B | 20.3 | 25.0 | 20.9 | +23.2% | +3.0% > 7 B | 88.9 | 107.5 | 155.7 | +20.9% | +75.1% > 8 B | 89.6 | 110.9 | 176.2 | +23.8% | +96.7% > 16 B | 134.4 | 172.4 | 334.8 | +28.3% | +149.1% > 31 B | 163.5 | 220.5 | 606.2 | +34.9% | +270.8% > 64 B | 203.8 | 235.9 | 968.6 | +15.8% | +375.3% > 127 B | 224.6 | 268.7 | 1362.8 | +19.6% | +506.8% > 512 B | 235.7 | 271.1 | 1913.7 | +15.0% | +711.9% > 1024 B| 256.8 | 290.6 | 2123.6 | +13.2% | +726.9% > 4096 B| 263.8 | 302.9 | 2290.4 | +14.8% | +768.2% > > Benchmark results (QEMU TCG, rv64, Unaligned - Offset 3): > > Len | Default | NoZBB | ZBB | %NoZBB | %ZBB > ------|---------|--------|--------|--------|------- > 1 B | 20.7 | 21.7 | 21.5 | +4.8% | +3.9% > 7 B | 96.2 | 99.1 | 96.9 | +3.0% | +0.7% > 8 B | 97.5 | 118.5 | 110.5 | +21.5% | +13.3% > 16 B | 136.7 | 166.6 | 172.8 | +21.9% | +26.4% > 31 B | 167.6 | 206.5 | 211.9 | +23.2% | +26.4% > 64 B | 204.4 | 229.9 | 240.3 | +12.5% | +17.6% > 127 B | 229.6 | 261.7 | 269.0 | +14.0% | +17.2% > 512 B | 245.5 | 260.8 | 269.9 | +6.2% | +9.9% > 1024 B| 246.9 | 261.2 | 283.5 | +5.8% | +14.8% > 4096 B| 250.7 | 295.8 | 299.7 | +18.0% | +19.5% > > Signed-off-by: Milan Tripkovic <[email protected]> > --- > arch/riscv/include/asm/string.h | 2 + > arch/riscv/lib/Makefile | 1 + > arch/riscv/lib/memcmp.S | 125 ++++++++++++++++++++++++++++++++ > arch/riscv/purgatory/Makefile | 5 +- > 4 files changed, 132 insertions(+), 1 deletion(-) > create mode 100644 arch/riscv/lib/memcmp.S > > diff --git a/arch/riscv/include/asm/string.h b/arch/riscv/include/asm/string.h > index 764ffe8f6..5c5299678 100644 > --- a/arch/riscv/include/asm/string.h > +++ b/arch/riscv/include/asm/string.h > @@ -18,6 +18,8 @@ extern asmlinkage void *__memcpy(void *, const void *, > size_t); > #define __HAVE_ARCH_MEMMOVE > extern asmlinkage void *memmove(void *, const void *, size_t); > extern asmlinkage void *__memmove(void *, const void *, size_t); > +#define __HAVE_ARCH_MEMCMP > +extern asmlinkage int memcmp(const void *, const void *, size_t); > > #if !(defined(CONFIG_KASAN_GENERIC) || defined(CONFIG_KASAN_SW_TAGS)) > #define __HAVE_ARCH_STRCMP > diff --git a/arch/riscv/lib/Makefile b/arch/riscv/lib/Makefile > index 6f767b2a3..b529e1be1 100644 > --- a/arch/riscv/lib/Makefile > +++ b/arch/riscv/lib/Makefile > @@ -3,6 +3,7 @@ lib-y += delay.o > lib-y += memcpy.o > lib-y += memset.o > lib-y += memmove.o > +lib-y += memcmp.o > ifeq ($(CONFIG_KASAN_GENERIC)$(CONFIG_KASAN_SW_TAGS),) > lib-y += strcmp.o > lib-y += strlen.o > diff --git a/arch/riscv/lib/memcmp.S b/arch/riscv/lib/memcmp.S > new file mode 100644 > index 000000000..a531e481c > --- /dev/null > +++ b/arch/riscv/lib/memcmp.S > @@ -0,0 +1,125 @@ > +/* SPDX-License-Identifier: GPL-2.0-only */ > + > +#include <linux/linkage.h> > +#include <asm/asm.h> > +#include <asm/alternative-macros.h> > +#include <asm/hwcap.h> > + > +/* int memcmp(const void *cs, const void *ct, size_t n) */ > +SYM_FUNC_START(memcmp) > + > + __ALTERNATIVE_CFG("nop", "j memcmp_zbb", 0, RISCV_ISA_EXT_ZBB, > + IS_ENABLED(CONFIG_RISCV_ISA_ZBB) && > IS_ENABLED(CONFIG_TOOLCHAIN_HAS_ZBB)) > +/* > + * Parameters > + * a0 - Pointer to first memory block (cs), also return value > + * a1 - Pointer to second memory block (ct) > + * a2 - Number of bytes to compare (n), transformed to end pointer (a0 + n) > + * > + * Returns > + * a0 - 0 if equal, positive if cs > ct, negative if cs < ct > + * > + * Clobbers > + * t0, t1 > + */ > + beqz a2, 2f > + add a2, a0, a2 > +1: > + lbu t0, 0(a0) > + lbu t1, 0(a1) > + bne t0, t1, 3f > + addi a0, a0, 1 > + addi a1, a1, 1 > + bne a0, a2, 1b > +2: > + li a0, 0 > + ret > +3: > + sub a0, t0, t1 > + ret > + > +#if defined(CONFIG_RISCV_ISA_ZBB) && defined(CONFIG_TOOLCHAIN_HAS_ZBB) > +memcmp_zbb: > + > +.option push > +.option arch,+zbb > +/* > + * Parameters > + * a0 - Pointer to first memory block (cs), also return value > + * a1 - Pointer to second memory block (ct) > + * a2 - Number of bytes to compare (n), decremented during loop > + * > + * Returns > + * a0 - 0 if equal, positive if cs > ct, negative if cs < ct > + * > + * Clobbers > + * t0, t1, t2, t3, t4 > + */ > + add t3, a0, a2 > + or t0, a0, a1 > + andi t0, t0, (SZREG - 1) > + bnez t0, 5f > + > + addi t4, t3, -SZREG > + bltu t4, a0, 7f > + > +1: > + REG_L t1, 0(a0) > + REG_L t2, 0(a1) > + bne t1, t2, 2f > + addi a0, a0, SZREG > + addi a1, a1, SZREG > + bleu a0, t4, 1b > + > +7: > + beq a0, t3, 4f > + REG_L t1, 0(a0) > + REG_L t2, 0(a1) > + > + sub t0, t3, a0 > + li t4, SZREG > + sub t0, t4, t0 > + slli t0, t0, 3 > + > +#ifndef CONFIG_CPU_BIG_ENDIAN > + rev8 t1, t1 > + rev8 t2, t2 > +#endif > + srl t1, t1, t0 > + srl t2, t2, t0 > + > + bne t1, t2, 8f > + li a0, 0 > + ret > +5: > + beq a0, t3, 4f > +6: > + lbu t1, 0(a0) > + lbu t2, 0(a1) > + bne t1, t2, 3f > + addi a0, a0, 1 > + addi a1, a1, 1 > + bne a0, t3, 6b > + > +4: li a0, 0 > + ret > +2: > +#ifndef CONFIG_CPU_BIG_ENDIAN > + rev8 t1, t1 > + rev8 t2, t2 > +#endif > +8: > + sltu a0, t2, t1 > + sltu t0, t1, t2 > + sub a0, a0, t0 > + ret > + > +3: > + sub a0, t1, t2 > + ret > + > +.option pop > +#endif > +SYM_FUNC_END(memcmp) > +SYM_FUNC_ALIAS(__pi_memcmp, memcmp) > +EXPORT_SYMBOL(memcmp) > diff --git a/arch/riscv/purgatory/Makefile b/arch/riscv/purgatory/Makefile > index b0358a78f..456929971 100644 > --- a/arch/riscv/purgatory/Makefile > +++ b/arch/riscv/purgatory/Makefile > @@ -1,6 +1,6 @@ > # SPDX-License-Identifier: GPL-2.0 > > -purgatory-y := purgatory.o sha256.o entry.o string.o ctype.o memcpy.o > memset.o > +purgatory-y := purgatory.o sha256.o entry.o string.o ctype.o memcpy.o > memset.o memcmp.o > ifeq ($(CONFIG_KASAN_GENERIC)$(CONFIG_KASAN_SW_TAGS),) > purgatory-y += strcmp.o strlen.o strncmp.o strnlen.o strchr.o strrchr.o > endif > @@ -41,6 +41,9 @@ $(obj)/strchr.o: $(srctree)/arch/riscv/lib/strchr.S FORCE > $(obj)/strrchr.o: $(srctree)/arch/riscv/lib/strrchr.S FORCE > $(call if_changed_rule,as_o_S) > > +$(obj)/memcmp.o: $(srctree)/arch/riscv/lib/memcmp.S FORCE > + $(call if_changed_rule,as_o_S) > + > CFLAGS_sha256.o := -D__DISABLE_EXPORTS -D__NO_FORTIFY > CFLAGS_string.o := -D__DISABLE_EXPORTS > CFLAGS_ctype.o := -D__DISABLE_EXPORTS
