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Tue, 19 May 2026 07:00:39 -0700 (PDT) From: Milan Tripkovic To: pjw@kernel.org, palmer@dabbelt.com, aou@eecs.berkeley.edu, kees@kernel.org Cc: alex@ghiti.fr, andy@kernel.org, linux-riscv@lists.infradead.org, linux-kernel@vger.kernel.org, linux-hardening@vger.kernel.org, Dusan.Stojkovic@rt-rk.com, Milan Tripkovic Subject: [PATCH v5 1/2] riscv: lib: add memcmp() implementation Date: Tue, 19 May 2026 16:00:28 +0200 Message-ID: <20260519140029.1190381-2-milant2002@gmail.com> X-Mailer: git-send-email 2.43.0 In-Reply-To: <20260519140029.1190381-1-milant2002@gmail.com> References: <20260519140029.1190381-1-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 word-aligned loads for the generic path and the ZBB extension for optimized sign resolution, with an assembly fallback for non-ZBB systems. Benchmark results (QEMU TCG, rv64): Len | Default |NoALIGN | ALIGN | %NoALIGN | %ALIGN ------|---------|--------|--------|----------|-------- 1 B | 20.3 | 21.5 | 20.9 | +5.9% | +3.0% 7 B | 88.9 | 96.9 | 155.7 | +9.0% | +75.1% 8 B | 89.6 | 110.5 | 176.2 | +23.3% | +96.7% 16 B | 134.4 | 172.8 | 334.8 | +28.6% | +149.1% 31 B | 163.5 | 211.9 | 606.2 | +29.6% | +270.8% 64 B | 203.8 | 240.3 | 968.6 | +17.9% | +375.3% 127 B | 224.6 | 269.0 | 1362.8 | +19.8% | +506.8% 512 B | 235.7 | 269.9 | 1913.7 | +14.5% | +711.9% 1024 B| 256.8 | 283.5 | 2123.6 | +10.4% | +726.9% 4096 B| 263.8 | 299.7 | 2290.4 | +13.6% | +768.2% =20 Signed-off-by: Milan Tripkovic --- v5 changes: - Optimized generic memcmp path with word-aligned loads. - Implemented non-ZBB fallback to byte comparison per review. - Link to v4: https://lore.kernel.org/all/20260518131407.1026049-2-mila= nt2002@gmail.com/ v2 changes: - Added alignment checks for buffers to avoid expensive misaligned load= s. - Optimized the loop using end-pointers to reduce per-iteration overhea= d. - Implemented word-aligned tail handling using ZBB shifts. - Removed redundant pointer equality (a0 =3D=3D a1) check. - Retained BE support via #ifndef; ZBB rev8 is used for the LE fast-pat= h. - Link to v1: https://lore.kernel.org/all/20260512141007.1193033-1-mila= nt2002@gmail.com/ arch/riscv/include/asm/string.h | 2 + arch/riscv/lib/Makefile | 1 + arch/riscv/lib/memcmp.S | 106 ++++++++++++++++++++++++++++++++ arch/riscv/purgatory/Makefile | 5 +- 4 files changed, 113 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 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 *, 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 6f767b2a3..b529e1be1 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 000000000..cb71cd5ae --- /dev/null +++ b/arch/riscv/lib/memcmp.S @@ -0,0 +1,106 @@ +/* SPDX-License-Identifier: GPL-2.0-only */ + +#include +#include +#include +#include + +#if defined(CONFIG_RISCV_ISA_ZBB) && defined(CONFIG_TOOLCHAIN_HAS_ZBB) +.option push +.option arch,+zbb +#endif + +/* int memcmp(const void *cs, const void *ct, size_t n) */ +SYM_FUNC_START(memcmp) +/* + * 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 + +#if defined(CONFIG_TOOLCHAIN_HAS_ZBB) +7: + __ALTERNATIVE_CFG("j 5f", "nop", 0, RISCV_ISA_EXT_ZBB, + IS_ENABLED(CONFIG_RISCV_ISA_ZBB)) + + 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 +#else + j 5f +#endif +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: +#if !defined(CONFIG_CPU_BIG_ENDIAN) && defined(CONFIG_TOOLCHAIN_HAS_ZBB) + __ALTERNATIVE_CFG("j 5b", "nop", 0, RISCV_ISA_EXT_ZBB, IS_ENABLED(CONFIG_= RISCV_ISA_ZBB)) + rev8 t1, t1 + rev8 t2, t2 +#elif !defined(CONFIG_CPU_BIG_ENDIAN) + j 5b +#endif +8: + sltu a0, t2, t1 + sltu t0, t1, t2 + sub a0, a0, t0 + ret + +3: + sub a0, t1, t2 + ret + +SYM_FUNC_END(memcmp) +SYM_FUNC_ALIAS(__pi_memcmp, memcmp) +EXPORT_SYMBOL(memcmp) + +#if defined(CONFIG_RISCV_ISA_ZBB) && defined(CONFIG_TOOLCHAIN_HAS_ZBB) +.option pop +#endif 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 =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 Mon May 25 01:57:42 2026 Received: from mail-wr1-f50.google.com (mail-wr1-f50.google.com [209.85.221.50]) (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 BABC24028E2 for ; 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charset="utf-8" From: Milan Tripkovic Extend the string benchmarking suite to include memcmp(). Extend the string unit test to include memcmp(). Signed-off-by: Milan Tripkovic --- v5 changes: - Removed redundant warm-up from test case - Link to v4: https://lore.kernel.org/all/20260518131407.1026049-2-mila= nt2002@gmail.com/ v4 changes: - Fixed build error: call to undeclared function 'STRING_BENCH' - Link to v3: https://lore.kernel.org/all/20260515141019.1234037-1-mila= nt2002@gmail.com/ v3 changes: - Split memcmp benchmark into wrapper (string_bench_memcmp) and worker function (do_string_bench_memcmp). - Removed all C99 mixed declarations; moved all variable declarations to the top of each function. - Converted len, iterations and loop counters in the benchmark to u64 to avoid implicit casts. - Cleaned up spacing, indentation and minor style issues. - Added #if defined(CONFIG_RISCV_ISA_ZBB)... in memcmp.S - Link to v2: https://lore.kernel.org/all/20260514121359.931999-1-milan= t2002@gmail.com/ v2 changes: - Fixed KUnit build failures for Clang and non-benchmark configs. - Link to v1: https://lore.kernel.org/all/20260512141007.1193033-1-mila= nt2002@gmail.com/ lib/tests/string_kunit.c | 110 +++++++++++++++++++++++++++++++++++++++ 1 file changed, 110 insertions(+) diff --git a/lib/tests/string_kunit.c b/lib/tests/string_kunit.c index 0819ace5b..7b14c0052 100644 --- a/lib/tests/string_kunit.c +++ b/lib/tests/string_kunit.c @@ -881,6 +881,114 @@ 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 unsigned int max_offset =3D 16; + const unsigned int max_len =3D 32; + const unsigned int buf_size =3D max_offset + max_len + 32; + u8 *buf1, *buf2; + unsigned int i, j, len, k; + int res; + + 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:%u j:%u len:%u", 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'; + res =3D memcmp(buf1 + i, buf2 + j, len); + KUNIT_EXPECT_NE_MSG(test, res, 0, + "Should detect difference at k:%u (i:%u j:%u len:%u)", + k, i, j, len); + if (buf1[i + k] < buf2[j + k]) + KUNIT_EXPECT_LT(test, res, 0); + else + KUNIT_EXPECT_GT(test, res, 0); + } + } + } + } +} + +#ifndef STRING_BENCH +#define STRING_BENCH(...) 0 +#endif + +static void do_string_bench_memcmp(struct kunit *test) +{ + char *buf1 =3D NULL; + char *buf2 =3D NULL; + const u64 lengths[] =3D { 1, 7, 8, 16, 32, 64, 128, 512, 1024, 4096}; + const int offsets[] =3D { 0, 1, 3, 7}; + const u64 max_len =3D 4096 + 64; + unsigned int o, i; + unsigned int off; + u64 len; + char *p1; + char *p2; + u64 iterations; + u64 elapsed; + u64 ns_per_call; + u64 mbps; + + 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 (o =3D 0; o < ARRAY_SIZE(offsets); o++) { + off =3D offsets[o]; + + for (i =3D 0; i < ARRAY_SIZE(lengths); i++) { + len =3D lengths[i]; + p1 =3D buf1; + p2 =3D buf2 + off; + iterations =3D (len < 512) ? 100000ULL : 10000ULL; + elapsed =3D STRING_BENCH(iterations, memcmp, p1, p2, len); + ns_per_call =3D div_u64(elapsed, iterations); + mbps =3D len ? div_u64(iterations * len * (NSEC_PER_SEC / MEGA), elapse= d) : 0; + + if (off =3D=3D 0) { + kunit_info(test, "bench_memcmp_aligned: len=3D%-4llu: %llu MB/s (%llu = ns/call)\n", + len, mbps, ns_per_call); + } else { + kunit_info(test, "bench_memcmp_unaligned(off=3D%u): len=3D%-4llu: %llu= MB/s (%llu ns/call)\n", + off, len, mbps, ns_per_call); + } + } + } + + vfree(buf1); + vfree(buf2); +} + +static void string_bench_memcmp(struct kunit *test) +{ + if (!IS_ENABLED(CONFIG_STRING_KUNIT_BENCH)) { + kunit_skip(test, "CONFIG_STRING_KUNIT_BENCH not enabled"); + return; + } + do_string_bench_memcmp(test); +} + static struct kunit_case string_test_cases[] =3D { KUNIT_CASE(string_test_memset16), KUNIT_CASE(string_test_memset32), @@ -910,6 +1018,8 @@ 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