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([2a02:908:1b4:dac0:609b:e733:f100:d3dd]) by smtp.gmail.com with ESMTPSA id a640c23a62f3a-b7cfa56a7f9sm822910466b.51.2025.12.13.03.23.54 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Sat, 13 Dec 2025 03:23:55 -0800 (PST) From: Osama Abdelkader To: Will Deacon , Mark Rutland , Catalin Marinas , linux-arm-kernel@lists.infradead.org, linux-perf-users@vger.kernel.org, linux-kernel@vger.kernel.org Cc: Osama Abdelkader Subject: [PATCH v2] arm64: hw_breakpoint: warn on invalid breakpoint length Date: Sat, 13 Dec 2025 12:23:35 +0100 Message-ID: <20251213112336.26503-1-osama.abdelkader@gmail.com> X-Mailer: git-send-email 2.43.0 Precedence: bulk X-Mailing-List: linux-perf-users@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: 8bit Some tools (e.g. perf) incorrectly assume that breakpoints should be sizeof(long), but this is wrong for AArch64 where breakpoints must be 4 bytes. Add a warning when we silently fix up the parameter so tool developers can get notified. This addresses the FIXME comment by adding diagnostic output rather than breaking existing tools by returning -EINVAL. Signed-off-by: Osama Abdelkader --- v2: fix warning messageline splitting --- arch/arm64/kernel/hw_breakpoint.c | 10 ++++++---- 1 file changed, 6 insertions(+), 4 deletions(-) diff --git a/arch/arm64/kernel/hw_breakpoint.c b/arch/arm64/kernel/hw_breakpoint.c index ab76b36dce82..cce306145d78 100644 --- a/arch/arm64/kernel/hw_breakpoint.c +++ b/arch/arm64/kernel/hw_breakpoint.c @@ -475,11 +475,13 @@ static int arch_build_bp_info(struct perf_event *bp, return -EINVAL; } else if (hw->ctrl.len != ARM_BREAKPOINT_LEN_4) { /* - * FIXME: Some tools (I'm looking at you perf) assume - * that breakpoints should be sizeof(long). This - * is nonsense. For now, we fix up the parameter - * but we should probably return -EINVAL instead. + * Some tools (e.g. perf) incorrectly assume that + * breakpoints should be sizeof(long). This is wrong + * for AArch64 where breakpoints must be 4 bytes. + * Warn the user and fix up the parameter. */ + pr_warn_once("hw_breakpoint: invalid AArch64 breakpoint length %d, fixing to 4 bytes\n", + hw->ctrl.len); hw->ctrl.len = ARM_BREAKPOINT_LEN_4; } } -- 2.43.0