From: Mao Han <han_mao@c-sky.com> To: Palmer Dabbelt <palmer@sifive.com> Cc: linux-riscv@lists.infradead.org, guoren@kernel.org, linux-kernel@vger.kernel.org Subject: Re: [PATCH 1/3] riscv: Add perf callchain support Date: Mon, 29 Apr 2019 16:39:40 +0800 [thread overview] Message-ID: <20190429083940.GA22718@vmh-VirtualBox> (raw) In-Reply-To: <mhng-dd1d2b4c-122f-48d8-ac56-1c6bff93f236@palmer-si-x1e> On Thu, Apr 25, 2019 at 02:11:00PM -0700, Palmer Dabbelt wrote: > On Thu, 11 Apr 2019 00:53:48 PDT (-0700), han_mao@c-sky.com wrote: > >+ if (!kstack_end((void *)frame->fp) && > >+ !((unsigned long)frame->fp & 0x3) && > >+ ((unsigned long)frame->fp >= TASK_SIZE)) { > >+ frame->ra = ((struct stackframe *)frame->fp - 1)->ra; > >+ frame->fp = ((struct stackframe *)frame->fp - 1)->fp; > > It looks like this depends on having a frame pointer? In that case, shouldn't > we add some Kconfig logic to make CONFIG_PERF_EVENTS select > -fno-omit-frame-pointer? Frame pointers aren't enabled by default on RISC-V > and therefor are unlikely to exist at all. > Yes, frame pointer is required for kernel backtrace, -fno-omit-frame-pointer should be added if frame pointer is not enabled by default on RISC-V. When I testing the callchain support with buildroot chunk git://git.busybox.net/buildroot cbf1d861fadb491eee6e3686019d8f67d7f4ad85 both kernel and user program have fp without adding any extra option, so I thought frame pointer was enabled by default. ffffffe0000009ee <kernel_init_freeable>: ffffffe0000009ee: 711d addi sp,sp,-96 ffffffe0000009f0: ec86 sd ra,88(sp) ffffffe0000009f2: e8a2 sd s0,80(sp) ffffffe0000009f4: e4a6 sd s1,72(sp) void test_3(void) { 10498: fe010113 addi sp,sp,-32 1049c: 00113c23 sd ra,24(sp) 104a0: 00813823 sd s0,16(sp) 104a4: 02010413 addi s0,sp,32 > >+ /* make sure CONFIG_FUNCTION_GRAPH_TRACER is turned on */ > > Should that also be mandated by a Kconfig? > Yes, it is required for ftrace_graph_ret_addr support. It's already default for ARCH_RV64I in Kconfig. > >+/* > >+ * This will be called when the target is in user mode > >+ * This function will only be called when we use > >+ * "PERF_SAMPLE_CALLCHAIN" in > >+ * kernel/events/core.c:perf_prepare_sample() > >+ * > >+ * How to trigger perf_callchain_[user/kernel] : > >+ * $ perf record -e cpu-clock --call-graph fp ./program > >+ * $ perf report --call-graph > >+ * > >+ * On RISC-V platform, the program being sampled and the C library > >+ * need to be compiled with * -mbacktrace, otherwise the user > > What is "-mbacktrace"? I don't remember that ever being a RISC-V GCC option, > and my compiler doesn't undersand it. It understands "-fbacktrace" but that > doesn't produce a frame pointer. > It's a csky specific option, I forget to modify the comment. So it should be -fno-omit-frame-pointer here. Thanks, Mao Han
WARNING: multiple messages have this Message-ID (diff)
From: Mao Han <han_mao@c-sky.com> To: Palmer Dabbelt <palmer@sifive.com> Cc: linux-riscv@lists.infradead.org, guoren@kernel.org, linux-kernel@vger.kernel.org Subject: Re: [PATCH 1/3] riscv: Add perf callchain support Date: Mon, 29 Apr 2019 16:39:40 +0800 [thread overview] Message-ID: <20190429083940.GA22718@vmh-VirtualBox> (raw) In-Reply-To: <mhng-dd1d2b4c-122f-48d8-ac56-1c6bff93f236@palmer-si-x1e> On Thu, Apr 25, 2019 at 02:11:00PM -0700, Palmer Dabbelt wrote: > On Thu, 11 Apr 2019 00:53:48 PDT (-0700), han_mao@c-sky.com wrote: > >+ if (!kstack_end((void *)frame->fp) && > >+ !((unsigned long)frame->fp & 0x3) && > >+ ((unsigned long)frame->fp >= TASK_SIZE)) { > >+ frame->ra = ((struct stackframe *)frame->fp - 1)->ra; > >+ frame->fp = ((struct stackframe *)frame->fp - 1)->fp; > > It looks like this depends on having a frame pointer? In that case, shouldn't > we add some Kconfig logic to make CONFIG_PERF_EVENTS select > -fno-omit-frame-pointer? Frame pointers aren't enabled by default on RISC-V > and therefor are unlikely to exist at all. > Yes, frame pointer is required for kernel backtrace, -fno-omit-frame-pointer should be added if frame pointer is not enabled by default on RISC-V. When I testing the callchain support with buildroot chunk git://git.busybox.net/buildroot cbf1d861fadb491eee6e3686019d8f67d7f4ad85 both kernel and user program have fp without adding any extra option, so I thought frame pointer was enabled by default. ffffffe0000009ee <kernel_init_freeable>: ffffffe0000009ee: 711d addi sp,sp,-96 ffffffe0000009f0: ec86 sd ra,88(sp) ffffffe0000009f2: e8a2 sd s0,80(sp) ffffffe0000009f4: e4a6 sd s1,72(sp) void test_3(void) { 10498: fe010113 addi sp,sp,-32 1049c: 00113c23 sd ra,24(sp) 104a0: 00813823 sd s0,16(sp) 104a4: 02010413 addi s0,sp,32 > >+ /* make sure CONFIG_FUNCTION_GRAPH_TRACER is turned on */ > > Should that also be mandated by a Kconfig? > Yes, it is required for ftrace_graph_ret_addr support. It's already default for ARCH_RV64I in Kconfig. > >+/* > >+ * This will be called when the target is in user mode > >+ * This function will only be called when we use > >+ * "PERF_SAMPLE_CALLCHAIN" in > >+ * kernel/events/core.c:perf_prepare_sample() > >+ * > >+ * How to trigger perf_callchain_[user/kernel] : > >+ * $ perf record -e cpu-clock --call-graph fp ./program > >+ * $ perf report --call-graph > >+ * > >+ * On RISC-V platform, the program being sampled and the C library > >+ * need to be compiled with * -mbacktrace, otherwise the user > > What is "-mbacktrace"? I don't remember that ever being a RISC-V GCC option, > and my compiler doesn't undersand it. It understands "-fbacktrace" but that > doesn't produce a frame pointer. > It's a csky specific option, I forget to modify the comment. So it should be -fno-omit-frame-pointer here. Thanks, Mao Han _______________________________________________ linux-riscv mailing list linux-riscv@lists.infradead.org http://lists.infradead.org/mailman/listinfo/linux-riscv
next prev parent reply other threads:[~2019-04-29 8:40 UTC|newest] Thread overview: 17+ messages / expand[flat|nested] mbox.gz Atom feed top 2019-04-11 7:53 [PATCH 0/3] riscv: Add perf callchain support Mao Han 2019-04-11 7:53 ` [PATCH 1/3] " Mao Han 2019-04-11 14:24 ` Christoph Hellwig 2019-04-25 21:11 ` Palmer Dabbelt 2019-04-29 8:39 ` Mao Han [this message] 2019-04-29 8:39 ` Mao Han 2019-04-11 7:53 ` [PATCH 2/3] riscv: Add support for perf registers sampling Mao Han 2019-04-25 21:11 ` Palmer Dabbelt 2019-04-29 8:42 ` Mao Han 2019-04-29 8:42 ` Mao Han 2019-04-11 7:53 ` [PATCH 3/3] riscv: Add support for libdw Mao Han 2019-04-25 21:11 ` Palmer Dabbelt 2019-04-29 8:45 ` Mao Han 2019-04-29 8:45 ` Mao Han 2019-04-11 14:14 ` [PATCH 0/3] riscv: Add perf callchain support Christoph Hellwig 2019-04-12 9:38 ` [PATCH 2/3] riscv: Add support for perf registers sampling Mao Han 2019-04-13 8:01 ` Christoph Hellwig
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