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Wed, 14 May 2025 13:28:19 -0700 (PDT) Received: from charlie.ba.rivosinc.com ([64.71.180.162]) by smtp.gmail.com with ESMTPSA id d9443c01a7336-22fc829ea8esm102403355ad.205.2025.05.14.13.28.18 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Wed, 14 May 2025 13:28:18 -0700 (PDT) From: Charlie Jenkins Date: Wed, 14 May 2025 13:28:10 -0700 Subject: [PATCH v2] riscv: Use RISCV_HWPROBE_KEY_MISALIGNED_SCALAR_PERF MIME-Version: 1.0 Message-Id: <20250514-fix_misaligned_access-v2-1-edcd49096aca@rivosinc.com> X-B4-Tracking: v=1; b=H4sIANn8JGgC/3WNwQrCMBBEf6Xs2UjTNI315H9IKTFZ2wVNJCtBK f13Y8GjxzfMvFmAMREyHKsFEmZiiqFAs6vAzTZMKMgXhqZudK2lEld6jXdie6MpoB+tc8gslJH moHTne6+gbB8JS3HznofCM/Ezpvd2k+U3/RnbP8YshRTOWzR915qL1KdEOTIFt3fxDsO6rh/mI YG5vQAAAA== X-Change-ID: 20250513-fix_misaligned_access-37178356d9d3 To: libc-alpha@sourceware.org, Evan Green , Adhemerval Zanella , enh Cc: Charlie Jenkins X-Mailer: b4 0.14.2 X-Developer-Signature: v=1; a=openpgp-sha256; l=3242; i=charlie@rivosinc.com; h=from:subject:message-id; bh=f1WUxJDXeYnG8cC7HExF8fsrgeXCtsDKiKzZbalqu34=; b=owGbwMvMwCXWx5hUnlvL8Y3xtFoSQ4bKn9tnex3nsgheFPUUcxTLLvaa4axuaxU641HwvZl6Z 6I+XbnSUcrCIMbFICumyMJzrYG59Y5+2VHRsgkwc1iZQIYwcHEKwEQ2LWJk2LXghOKNh0sj1AwT 9OpqYlSnWbzxL5sfW3zF5P40GRalOwx/hZ4H/NQ6u7bSeHZLukUUa63DnveBWtPzvY6s4dD1qH/ KDQA= X-Developer-Key: i=charlie@rivosinc.com; a=openpgp; fpr=7D834FF11B1D8387E61C776FFB10D1F27D6B1354 X-Spam-Status: No, score=-12.4 required=5.0 tests=BAYES_00, DKIM_SIGNED, DKIM_VALID, GIT_PATCH_0, KAM_LOTSOFHASH, RCVD_IN_DNSWL_NONE, SPF_HELO_NONE, SPF_PASS, TXREP autolearn=ham autolearn_force=no version=3.4.6 X-Spam-Checker-Version: SpamAssassin 3.4.6 (2021-04-09) on server2.sourceware.org X-BeenThere: libc-alpha@sourceware.org X-Mailman-Version: 2.1.30 Precedence: list List-Id: Libc-alpha mailing list List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Errors-To: libc-alpha-bounces~patchwork=sourceware.org@sourceware.org RISCV_HWPROBE_KEY_CPUPERF_0 was deprecated by Linux in commit c42e2f076769 ("RISC-V: hwprobe: Add MISALIGNED_PERF key") because of an issue with the WHICH_CPUS flag improperly checking the value as a bitmask in hwprobe. This doesn't cause a functional problem with glibc because glibc isn't using the WHICH_CPUS flag. However, to avoid using deprecated interfaces, switch to using RISCV_HWPROBE_KEY_MISALIGNED_SCALAR_PERF instead of RISCV_HWPROBE_KEY_CPUPERF_0. Signed-off-by: Charlie Jenkins --- Tested by using the kernel flags RISCV_SLOW_UNALIGNED_ACCESS and RISCV_EFFICIENT_UNALIGNED_ACCESS which cause the Linux kernel to report slow/fast unaligned accesses respectively through hwprobe and checking that the proper code path was being used. --- Changes in v2: - I could not do simple math and though there was bug that didn't exist. I changed the patch description to only talk about how the hwprobe key is deprecated rather than inventing a bug. - Link to v1: https://inbox.sourceware.org/20250514-fix_misaligned_access-v1-1-cdae79647b15@rivosinc.com --- sysdeps/unix/sysv/linux/riscv/multiarch/ifunc-impl-list.c | 5 ++--- sysdeps/unix/sysv/linux/riscv/multiarch/memcpy.c | 4 ++-- 2 files changed, 4 insertions(+), 5 deletions(-) --- base-commit: ad966bc4efd9e69cbbda2073121cc68f1deb9588 change-id: 20250513-fix_misaligned_access-37178356d9d3 diff --git a/sysdeps/unix/sysv/linux/riscv/multiarch/ifunc-impl-list.c b/sysdeps/unix/sysv/linux/riscv/multiarch/ifunc-impl-list.c index 1c1deca8f664cab9726895d723b3a3f11e3b3f14..ce620fa20a499b166c08efbbb4677d5df6f8a39d 100644 --- a/sysdeps/unix/sysv/linux/riscv/multiarch/ifunc-impl-list.c +++ b/sysdeps/unix/sysv/linux/riscv/multiarch/ifunc-impl-list.c @@ -28,10 +28,9 @@ __libc_ifunc_impl_list (const char *name, struct libc_ifunc_impl *array, bool fast_unaligned = false; - struct riscv_hwprobe pair = { .key = RISCV_HWPROBE_KEY_CPUPERF_0 }; + struct riscv_hwprobe pair = { .key = RISCV_HWPROBE_KEY_MISALIGNED_SCALAR_PERF }; if (__riscv_hwprobe (&pair, 1, 0, NULL, 0) == 0 - && (pair.value & RISCV_HWPROBE_MISALIGNED_MASK) - == RISCV_HWPROBE_MISALIGNED_FAST) + && pair.value == RISCV_HWPROBE_MISALIGNED_SCALAR_FAST) fast_unaligned = true; IFUNC_IMPL (i, name, memcpy, diff --git a/sysdeps/unix/sysv/linux/riscv/multiarch/memcpy.c b/sysdeps/unix/sysv/linux/riscv/multiarch/memcpy.c index 8544f5402ab3e8d6e82b82dfa0c95ec14e665519..6d8cb5a3ad045ee953746d0ae6dce002d9d29960 100644 --- a/sysdeps/unix/sysv/linux/riscv/multiarch/memcpy.c +++ b/sysdeps/unix/sysv/linux/riscv/multiarch/memcpy.c @@ -37,8 +37,8 @@ static inline __typeof (__redirect_memcpy) * select_memcpy_ifunc (uint64_t dl_hwcap, __riscv_hwprobe_t hwprobe_func) { unsigned long long int v; - if (__riscv_hwprobe_one (hwprobe_func, RISCV_HWPROBE_KEY_CPUPERF_0, &v) == 0 - && (v & RISCV_HWPROBE_MISALIGNED_MASK) == RISCV_HWPROBE_MISALIGNED_FAST) + if (__riscv_hwprobe_one (hwprobe_func, RISCV_HWPROBE_KEY_MISALIGNED_SCALAR_PERF, &v) == 0 + && v == RISCV_HWPROBE_MISALIGNED_SCALAR_FAST) return __memcpy_noalignment; return __memcpy_generic;