Messages in this thread Patch in this message | | | From | Alexandre Truong <> | Subject | [PATCH v2 4/4] perf tools: determine if LR is the return address | Date | Fri, 12 Feb 2021 17:03:43 +0000 |
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On arm64 and frame pointer mode (e.g: perf record --callgraph fp), use dwarf unwind info to check if the link register is the return address in order to inject it to the frame pointer stack.
Write the following application:
int a = 10;
void f2(void) { for (int i = 0; i < 1000000; i++) a *= a; }
void f1() { for (int i = 0; i < 10; i++) f2(); }
int main (void) { f1(); return 0; }
with the following compilation flags: gcc -fno-omit-frame-pointer -fno-inline -O2
The compiler omits the frame pointer for f2 on arm. This is a problem with any leaf call, for example an application with many different calls to malloc() would always omit the calling frame, even if it can be determined.
./perf record --call-graph fp ./a.out ./perf report
currently gives the following stack:
0xffffea52f361 _start __libc_start_main main f2
After this change, perf report correctly shows f1() calling f2(), even though it was missing from the frame pointer unwind:
./perf report
0xffffea52f361 _start __libc_start_main main f1 f2
Signed-off-by: Alexandre Truong <alexandre.truong@arm.com> --- tools/perf/util/Build | 1 + .../util/arm-frame-pointer-unwind-support.c | 44 +++++++++++++++++++ .../util/arm-frame-pointer-unwind-support.h | 7 +++ tools/perf/util/machine.c | 9 ++-- 4 files changed, 58 insertions(+), 3 deletions(-) create mode 100644 tools/perf/util/arm-frame-pointer-unwind-support.c create mode 100644 tools/perf/util/arm-frame-pointer-unwind-support.h
diff --git a/tools/perf/util/Build b/tools/perf/util/Build index 188521f34347..3b82cb992bce 100644 --- a/tools/perf/util/Build +++ b/tools/perf/util/Build @@ -1,3 +1,4 @@ +perf-y += arm-frame-pointer-unwind-support.o perf-y += annotate.o perf-y += block-info.o perf-y += block-range.o diff --git a/tools/perf/util/arm-frame-pointer-unwind-support.c b/tools/perf/util/arm-frame-pointer-unwind-support.c new file mode 100644 index 000000000000..964efd08e72e --- /dev/null +++ b/tools/perf/util/arm-frame-pointer-unwind-support.c @@ -0,0 +1,44 @@ +// SPDX-License-Identifier: GPL-2.0 +#include "../arch/arm64/include/uapi/asm/perf_regs.h" +#include "arch/arm64/include/perf_regs.h" +#include "event.h" +#include "arm-frame-pointer-unwind-support.h" +#include "callchain.h" +#include "unwind.h" + +struct entries { + u64 stack[2]; + size_t length; +}; + +static bool get_leaf_frame_caller_enabled(struct perf_sample *sample) +{ + return callchain_param.record_mode == CALLCHAIN_FP && sample->user_regs.regs + && sample->user_regs.mask == PERF_REGS_MASK; +} + +static int add_entry(struct unwind_entry *entry, void *arg) +{ + struct entries *entries = arg; + + entries->stack[entries->length++] = entry->ip; + return 0; +} + +u64 get_leaf_frame_caller_aarch64(struct perf_sample *sample, struct thread *thread) +{ + int ret; + + struct entries entries = {{0, 0}, 0}; + + if (!get_leaf_frame_caller_enabled(sample)) + return 0; + + ret = unwind__get_entries(add_entry, &entries, thread, sample, 2); + + if (ret || entries.length != 2) + return ret; + + return callchain_param.order == ORDER_CALLER ? + entries.stack[0] : entries.stack[1]; +} diff --git a/tools/perf/util/arm-frame-pointer-unwind-support.h b/tools/perf/util/arm-frame-pointer-unwind-support.h new file mode 100644 index 000000000000..16dc03fa9abe --- /dev/null +++ b/tools/perf/util/arm-frame-pointer-unwind-support.h @@ -0,0 +1,7 @@ +/* SPDX-License-Identifier: GPL-2.0 */ +#ifndef __PERF_ARM_FRAME_POINTER_UNWIND_SUPPORT_H +#define __PERF_ARM_FRAME_POINTER_UNWIND_SUPPORT_H + +u64 get_leaf_frame_caller_aarch64(struct perf_sample *sample, struct thread *thread); + +#endif /* __PERF_ARM_FRAME_POINTER_UNWIND_SUPPORT_H */ diff --git a/tools/perf/util/machine.c b/tools/perf/util/machine.c index 7f03ffa016b0..dfb72dbc0e2d 100644 --- a/tools/perf/util/machine.c +++ b/tools/perf/util/machine.c @@ -34,6 +34,7 @@ #include "bpf-event.h" #include <internal/lib.h> // page_size #include "cgroup.h" +#include "arm-frame-pointer-unwind-support.h" #include <linux/ctype.h> #include <symbol/kallsyms.h> @@ -2671,10 +2672,12 @@ static int find_prev_cpumode(struct ip_callchain *chain, struct thread *thread, return err; } -static u64 get_leaf_frame_caller(struct perf_sample *sample __maybe_unused, - struct thread *thread __maybe_unused) +static u64 get_leaf_frame_caller(struct perf_sample *sample, struct thread *thread) { - return 0; + if (strncmp(thread->maps->machine->env->arch, "aarch64", 7) == 0) + return get_leaf_frame_caller_aarch64(sample, thread); + else + return 0; } static int thread__resolve_callchain_sample(struct thread *thread, -- 2.23.0
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