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Wed, 14 May 2025 12:15:25 -0700 (PDT) Received: from charlie.ba.rivosinc.com ([64.71.180.162]) by smtp.gmail.com with ESMTPSA id d9443c01a7336-22fc828b3a0sm103590795ad.179.2025.05.14.12.15.24 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Wed, 14 May 2025 12:15:25 -0700 (PDT) From: Charlie Jenkins Date: Wed, 14 May 2025 12:15:12 -0700 Subject: [PATCH] riscv: Fix alignment-ignorant memcpy hwprobe MIME-Version: 1.0 Message-Id: <20250514-fix_misaligned_access-v1-1-cdae79647b15@rivosinc.com> X-B4-Tracking: v=1; b=H4sIAL/rJGgC/x2MQQqAIBAAvxJ7TsjErL4SEaKbLZSFCxFIf086D sxMBsZEyDBWGRLexHTGArKuwG02BhTkC0PbtLrRUomVnuUgtjuFiH6xziGzUEaaXunOD15Baa+ ERfy/0/y+H2XtDeJnAAAA X-Change-ID: 20250513-fix_misaligned_access-37178356d9d3 To: libc-alpha@sourceware.org, Evan Green , Adhemerval Zanella Cc: Charlie Jenkins X-Mailer: b4 0.14.2 X-Developer-Signature: v=1; a=openpgp-sha256; l=3196; i=charlie@rivosinc.com; h=from:subject:message-id; bh=T+2sPV8umO3ncYql49bYWjVaB/JEB0odaB6ACcFOTEU=; b=owGbwMvMwCXWx5hUnlvL8Y3xtFoSQ4bK62OXZzf/1rquJGx8m+3pUYbYTYdyi69WPUotOHg+T e2dWNzVjlIWBjEuBlkxRRaeaw3MrXf0y46Klk2AmcPKBDKEgYtTACbSvIvhn6mKUvLEU22xTTXn Z76tqldZ7cke0yH90CPk0vSv/DP3v2FkWLBecNn8R02/u70OcJl1SLZm6i9pOSB+eF9t1srN22a tYwYA 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 The hwprobe API for RISCV_HWPROBE_KEY_CPUPERF_0 had some unforutunate wording. It included a value labeled RISCV_HWPROBE_MISALIGNED_MASK which was not, in fact, a mask but rather a maximum value. This code fell for the trap and used RISCV_HWPROBE_MISALIGNED_MASK as a mask, so "(pair.value & RISCV_HWPROBE_MISALIGNED_MASK) == RISCV_HWPROBE_MISALIGNED_FAST" ends up being "(pair.value & (7 << 0)) == (3 << 0)" which will always evaluate to false. Because of this wording issue, RISCV_HWPROBE_KEY_CPUPERF_0 was deprecated by Linux in commit c42e2f076769 ("RISC-V: hwprobe: Add MISALIGNED_PERF key"). Change the hwprobe call to use RISCV_HWPROBE_KEY_MISALIGNED_SCALAR_PERF instead to fix this issue and have the hwprobe call succeed. 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. --- 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;