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Wed, 24 Sep 2025 23:50:26 -0700 (PDT) Received: from krava ([2a02:8308:a00c:e200::31e0]) by smtp.gmail.com with ESMTPSA id 5b1f17b1804b1-46e33bf6ecbsm20412955e9.22.2025.09.24.23.50.25 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Wed, 24 Sep 2025 23:50:26 -0700 (PDT) From: Jiri Olsa X-Google-Original-From: Jiri Olsa Date: Thu, 25 Sep 2025 08:50:24 +0200 To: Feng Yang Cc: rostedt@goodmis.org, mhiramat@kernel.org, mark.rutland@arm.com, catalin.marinas@arm.com, will@kernel.org, revest@chromium.org, alexei.starovoitov@gmail.com, olsajiri@gmail.com, andrii@kernel.org, ast@kernel.org, linux-kernel@vger.kernel.org, linux-trace-kernel@vger.kernel.org, linux-arm-kernel@lists.infradead.org, bpf@vger.kernel.org Subject: Re: [PATCH] tracing: Fix the bug where bpf_get_stackid returns -EFAULT on the ARM64 Message-ID: References: <20250925020822.119302-1-yangfeng59949@163.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20250925020822.119302-1-yangfeng59949@163.com> X-CRM114-Version: 20100106-BlameMichelson ( TRE 0.8.0 (BSD) ) MR-646709E3 X-CRM114-CacheID: sfid-20250924_235029_230460_56E21A67 X-CRM114-Status: GOOD ( 22.43 ) X-BeenThere: linux-arm-kernel@lists.infradead.org X-Mailman-Version: 2.1.34 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Sender: "linux-arm-kernel" Errors-To: linux-arm-kernel-bounces+linux-arm-kernel=archiver.kernel.org@lists.infradead.org On Thu, Sep 25, 2025 at 10:08:22AM +0800, Feng Yang wrote: > From: Feng Yang > > When using bpf_program__attach_kprobe_multi_opts on ARM64 to hook a BPF program > that contains the bpf_get_stackid function, the BPF program fails > to obtain the stack trace and returns -EFAULT. > > This is because ftrace_partial_regs omits the configuration of the pstate register, > leaving pstate at the default value of 0. When get_perf_callchain executes, > it uses user_mode(regs) to determine whether it is in kernel mode. > This leads to a misjudgment that the code is in user mode, > so perf_callchain_kernel is not executed and the function returns directly. > As a result, trace->nr becomes 0, and finally -EFAULT is returned. > > Therefore, the assignment of the pstate register is added here. > > Fixes: b9b55c8912ce ("tracing: Add ftrace_partial_regs() for converting ftrace_regs to pt_regs") > Closes: https://lore.kernel.org/bpf/20250919071902.554223-1-yangfeng59949@163.com/ > Signed-off-by: Feng Yang Tested-by: Jiri Olsa thanks, jirka > --- > arch/arm64/include/asm/ftrace.h | 1 + > 1 file changed, 1 insertion(+) > > diff --git a/arch/arm64/include/asm/ftrace.h b/arch/arm64/include/asm/ftrace.h > index bfe3ce9df197..ba7cf7fec5e9 100644 > --- a/arch/arm64/include/asm/ftrace.h > +++ b/arch/arm64/include/asm/ftrace.h > @@ -153,6 +153,7 @@ ftrace_partial_regs(const struct ftrace_regs *fregs, struct pt_regs *regs) > regs->pc = afregs->pc; > regs->regs[29] = afregs->fp; > regs->regs[30] = afregs->lr; > + regs->pstate = PSR_MODE_EL1h; > return regs; > } > > -- > 2.25.1 >