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Thu, 14 May 2026 05:14:19 -0700 (PDT) From: Milan Tripkovic To: Paul Walmsley , Palmer Dabbelt , Albert Ou Cc: Alexandre Ghiti , Kees Cook , Andy Shevchenko , Nathan Chancellor , Nick Desaulniers , Bill Wendling , Justin Stitt , linux-riscv@lists.infradead.org, linux-kernel@vger.kernel.org, linux-hardening@vger.kernel.org, llvm@lists.linux.dev, Dusan Stojkovic , Milan Tripkovic Subject: [PATCH v2 1/2] riscv: lib: add memcmp() implementation Date: Thu, 14 May 2026 14:13:57 +0200 Message-ID: <20260514121359.931999-2-milant2002@gmail.com> X-Mailer: git-send-email 2.43.0 In-Reply-To: <20260514121359.931999-1-milant2002@gmail.com> References: <20260514121359.931999-1-milant2002@gmail.com> Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: quoted-printable Content-Type: text/plain; charset="utf-8" From: Milan Tripkovic 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. 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% =20 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 --- arch/riscv/include/asm/string.h | 2 + arch/riscv/lib/Makefile | 1 + arch/riscv/lib/memcmp.S | 124 ++++++++++++++++++++++++++++++++ arch/riscv/purgatory/Makefile | 5 +- 4 files changed, 131 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/strin= g.h index 764ffe8f6479..5c5299678c66 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 *, si= ze_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); =20 #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 6f767b2a349d..b529e1be18b2 100644 --- a/arch/riscv/lib/Makefile +++ b/arch/riscv/lib/Makefile @@ -3,6 +3,7 @@ lib-y +=3D delay.o lib-y +=3D memcpy.o lib-y +=3D memset.o lib-y +=3D memmove.o +lib-y +=3D memcmp.o ifeq ($(CONFIG_KASAN_GENERIC)$(CONFIG_KASAN_SW_TAGS),) lib-y +=3D strcmp.o lib-y +=3D strlen.o diff --git a/arch/riscv/lib/memcmp.S b/arch/riscv/lib/memcmp.S new file mode 100644 index 000000000000..f7d0eaa08880 --- /dev/null +++ b/arch/riscv/lib/memcmp.S @@ -0,0 +1,124 @@ +/* SPDX-License-Identifier: GPL-2.0-only */ + +#include +#include +#include +#include + +/* 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 + + +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 + +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 b0358a78f11a..456929971da7 100644 --- a/arch/riscv/purgatory/Makefile +++ b/arch/riscv/purgatory/Makefile @@ -1,6 +1,6 @@ # SPDX-License-Identifier: GPL-2.0 =20 -purgatory-y :=3D purgatory.o sha256.o entry.o string.o ctype.o memcpy.o me= mset.o +purgatory-y :=3D purgatory.o sha256.o entry.o string.o ctype.o memcpy.o me= mset.o memcmp.o ifeq ($(CONFIG_KASAN_GENERIC)$(CONFIG_KASAN_SW_TAGS),) purgatory-y +=3D 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 $(call if_changed_rule,as_o_S) =20 +$(obj)/memcmp.o: $(srctree)/arch/riscv/lib/memcmp.S FORCE + $(call if_changed_rule,as_o_S) + CFLAGS_sha256.o :=3D -D__DISABLE_EXPORTS -D__NO_FORTIFY CFLAGS_string.o :=3D -D__DISABLE_EXPORTS CFLAGS_ctype.o :=3D -D__DISABLE_EXPORTS --=20 2.43.0 From nobody Fri Jun 12 13:55:57 2026 Received: from mail-wm1-f47.google.com (mail-wm1-f47.google.com [209.85.128.47]) (using TLSv1.2 with cipher ECDHE-RSA-AES128-GCM-SHA256 (128/128 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id C712C3C9882 for ; 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Thu, 14 May 2026 05:14:21 -0700 (PDT) Received: from RTRKW671-LIN.domain.local ([77.243.27.125]) by smtp.gmail.com with ESMTPSA id ffacd0b85a97d-45d9e767cb9sm6285630f8f.2.2026.05.14.05.14.19 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Thu, 14 May 2026 05:14:20 -0700 (PDT) From: Milan Tripkovic To: Paul Walmsley , Palmer Dabbelt , Albert Ou Cc: Alexandre Ghiti , Kees Cook , Andy Shevchenko , Nathan Chancellor , Nick Desaulniers , Bill Wendling , Justin Stitt , linux-riscv@lists.infradead.org, linux-kernel@vger.kernel.org, linux-hardening@vger.kernel.org, llvm@lists.linux.dev, Dusan Stojkovic , Milan Tripkovic , kernel test robot Subject: [PATCH v2 2/2] lib/string_kunit: extend benchmarks and unit test to memcmp() Date: Thu, 14 May 2026 14:13:58 +0200 Message-ID: <20260514121359.931999-3-milant2002@gmail.com> X-Mailer: git-send-email 2.43.0 In-Reply-To: <20260514121359.931999-1-milant2002@gmail.com> References: <20260514121359.931999-1-milant2002@gmail.com> Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: quoted-printable Content-Type: text/plain; charset="utf-8" From: Milan Tripkovic Extend the string benchmarking suite to include memcmp(). Extend the string unit test to include memcmp(). Reported-by: kernel test robot Closes: https://lore.kernel.org/oe-kbuild-all/202605140827.Qg1DZpcB-lkp@int= el.com/ Signed-off-by: Milan Tripkovic --- lib/tests/string_kunit.c | 106 +++++++++++++++++++++++++++++++++++++++ 1 file changed, 106 insertions(+) diff --git a/lib/tests/string_kunit.c b/lib/tests/string_kunit.c index 0819ace5b027..d0bad40a719a 100644 --- a/lib/tests/string_kunit.c +++ b/lib/tests/string_kunit.c @@ -881,6 +881,110 @@ static void string_bench_strrchr(struct kunit *test) STRING_BENCH_BUF(test, buf, len, strrchr, buf, '\0'); } =20 +static void string_test_memcmp(struct kunit *test) +{ + const int max_offset =3D 16; + const int max_len =3D 32; + const int buf_size =3D max_offset + max_len + 32; + u8 *buf1, *buf2; + int i, j, len, k; + + buf1 =3D kunit_kzalloc(test, buf_size, GFP_KERNEL); + buf2 =3D kunit_kzalloc(test, buf_size, GFP_KERNEL); + KUNIT_ASSERT_NOT_ERR_OR_NULL(test, buf1); + KUNIT_ASSERT_NOT_ERR_OR_NULL(test, buf2); + + for (i =3D 0; i < max_offset; i++) { + for (j =3D 0; j < max_offset; j++) { + for (len =3D 0; len <=3D max_len; len++) { + memset(buf1, 'A', buf_size); + memset(buf2, 'A', buf_size); + KUNIT_EXPECT_EQ_MSG(test, memcmp(buf1 + i, buf2 + j, len), 0, + "Should be equal: i:%d j:%d len:%d", i, j, len); + for (k =3D 0; k < len; k++) { + memset(buf1, 'A', buf_size); + memset(buf2, 'A', buf_size); + buf2[j + k] =3D 'B'; + int res =3D memcmp(buf1 + i, buf2 + j, len); + + KUNIT_EXPECT_NE_MSG(test, res, 0, + "Should detect difference at k:%d (i:%d j:%d len:%d)", + k, i, j, len); + + if (buf1[i + k] < buf2[j + k]) + KUNIT_EXPECT_LT(test, res, 0); + else + KUNIT_EXPECT_GT(test, res, 0); + } + } + } + } +} + +#if IS_ENABLED(CONFIG_STRING_KUNIT_BENCH) +static void string_bench_memcmp(struct kunit *test) +{ + char *buf1, *buf2; + size_t lengths[] =3D { 1, 7, 8, 16, 32, 64, 128, 512, 1024, 4096}; + int offsets[] =3D {0, 1, 3, 7}; + const size_t max_len =3D 4096 + 64; + + buf1 =3D vmalloc(max_len); + buf2 =3D vmalloc(max_len); + + if (!buf1 || !buf2) { + vfree(buf1); + vfree(buf2); + kunit_err(test, "vmalloc failed\n"); + return; + } + + memset(buf1, 'A', max_len); + memset(buf2, 'A', max_len); + + for (int i =3D 0; i < 100000; i++) + (void)memcmp(buf1, buf2, 4096); + + for (int o =3D 0; o < ARRAY_SIZE(offsets); o++) { + int off =3D offsets[o]; + + for (int i =3D 0; i < ARRAY_SIZE(lengths); i++) { + size_t len =3D lengths[i]; + char *p1 =3D buf1; + char *p2 =3D buf2 + off; + + u32 iterations =3D (len < 512) ? 100000 : 10000; + + for (u32 j =3D 0; j < iterations; j++) { + (void)memcmp(p1, p2, len); + barrier(); + } + + u64 elapsed =3D STRING_BENCH(iterations, memcmp, p1, p2, len); + u64 ns_per_call =3D div_u64(elapsed, iterations); + u64 mbps =3D len ? div_u64((u64)len * iterations * 1000, + elapsed) : 0; + + if (off =3D=3D 0) { + kunit_info(test, "bench_memcmp_aligned: len=3D%-4zu: %llu MB/s (%llu n= s/call)\n", + len, mbps, ns_per_call); + } else { + kunit_info(test, "bench_memcmp_unaligned(off=3D%d): len=3D%-4zu: %llu = MB/s (%llu ns/call)\n", + off, len, mbps, ns_per_call); + } + } + } + + vfree(buf1); + vfree(buf2); +} +#else +static void string_bench_memcmp(struct kunit *test) +{ + kunit_skip(test, "not enabled"); +} +#endif + static struct kunit_case string_test_cases[] =3D { KUNIT_CASE(string_test_memset16), KUNIT_CASE(string_test_memset32), @@ -910,6 +1014,8 @@ static struct kunit_case string_test_cases[] =3D { KUNIT_CASE(string_bench_strnlen), KUNIT_CASE(string_bench_strchr), KUNIT_CASE(string_bench_strrchr), + KUNIT_CASE(string_test_memcmp), + KUNIT_CASE_SLOW(string_bench_memcmp), {} }; =20 --=20 2.43.0