[PATCH v4 6/6] perf tools: determine if LR is the return address
German Gomez
german.gomez at arm.com
Wed Dec 15 07:11:38 PST 2021
From: Alexandre Truong <alexandre.truong at arm.com>
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 at arm.com>
Signed-off-by: German Gomez <german.gomez at arm.com>
---
tools/perf/util/Build | 1 +
.../util/arm64-frame-pointer-unwind-support.c | 63 +++++++++++++++++++
.../util/arm64-frame-pointer-unwind-support.h | 10 +++
tools/perf/util/machine.c | 19 ++++--
tools/perf/util/machine.h | 1 +
5 files changed, 89 insertions(+), 5 deletions(-)
create mode 100644 tools/perf/util/arm64-frame-pointer-unwind-support.c
create mode 100644 tools/perf/util/arm64-frame-pointer-unwind-support.h
diff --git a/tools/perf/util/Build b/tools/perf/util/Build
index 2e5bfbb69960..03d4c647bd86 100644
--- a/tools/perf/util/Build
+++ b/tools/perf/util/Build
@@ -1,3 +1,4 @@
+perf-y += arm64-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/arm64-frame-pointer-unwind-support.c b/tools/perf/util/arm64-frame-pointer-unwind-support.c
new file mode 100644
index 000000000000..4f5ecf51ed38
--- /dev/null
+++ b/tools/perf/util/arm64-frame-pointer-unwind-support.c
@@ -0,0 +1,63 @@
+// SPDX-License-Identifier: GPL-2.0
+#include "arm64-frame-pointer-unwind-support.h"
+#include "callchain.h"
+#include "event.h"
+#include "perf_regs.h" // SMPL_REG_MASK
+#include "unwind.h"
+
+#define perf_event_arm_regs perf_event_arm64_regs
+#include "../arch/arm64/include/uapi/asm/perf_regs.h"
+#undef perf_event_arm_regs
+
+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 & SMPL_REG_MASK(PERF_REG_ARM64_LR);
+}
+
+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 usr_idx)
+{
+ int ret;
+ struct entries entries = {};
+ struct regs_dump old_regs = sample->user_regs;
+
+ if (!get_leaf_frame_caller_enabled(sample))
+ return 0;
+
+ /*
+ * If PC and SP are not recorded, get the value of PC from the stack
+ * and set its mask. SP is not used when doing the unwinding but it
+ * still needs to be set to prevent failures.
+ */
+
+ if (!(sample->user_regs.mask & SMPL_REG_MASK(PERF_REG_ARM64_PC))) {
+ sample->user_regs.cache_mask |= SMPL_REG_MASK(PERF_REG_ARM64_PC);
+ sample->user_regs.cache_regs[PERF_REG_ARM64_PC] = sample->callchain->ips[usr_idx+1];
+ }
+
+ if (!(sample->user_regs.mask & SMPL_REG_MASK(PERF_REG_ARM64_SP))) {
+ sample->user_regs.cache_mask |= SMPL_REG_MASK(PERF_REG_ARM64_SP);
+ sample->user_regs.cache_regs[PERF_REG_ARM64_SP] = 0;
+ }
+
+ ret = unwind__get_entries(add_entry, &entries, thread, sample, 2);
+ sample->user_regs = old_regs;
+
+ 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/arm64-frame-pointer-unwind-support.h b/tools/perf/util/arm64-frame-pointer-unwind-support.h
new file mode 100644
index 000000000000..32af9ce94398
--- /dev/null
+++ b/tools/perf/util/arm64-frame-pointer-unwind-support.h
@@ -0,0 +1,10 @@
+/* SPDX-License-Identifier: GPL-2.0 */
+#ifndef __PERF_ARM_FRAME_POINTER_UNWIND_SUPPORT_H
+#define __PERF_ARM_FRAME_POINTER_UNWIND_SUPPORT_H
+
+#include "event.h"
+#include "thread.h"
+
+u64 get_leaf_frame_caller_aarch64(struct perf_sample *sample, struct thread *thread, int user_idx);
+
+#endif /* __PERF_ARM_FRAME_POINTER_UNWIND_SUPPORT_H */
diff --git a/tools/perf/util/machine.c b/tools/perf/util/machine.c
index 3eddad009f78..a00fd6796b35 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 "arm64-frame-pointer-unwind-support.h"
#include <linux/ctype.h>
#include <symbol/kallsyms.h>
@@ -2710,10 +2711,13 @@ 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, int usr_idx __maybe_unused)
+static u64 get_leaf_frame_caller(struct perf_sample *sample,
+ struct thread *thread, int usr_idx)
{
- return 0;
+ if (machine__normalize_is(thread->maps->machine, "arm64"))
+ return get_leaf_frame_caller_aarch64(sample, thread, usr_idx);
+ else
+ return 0;
}
static int thread__resolve_callchain_sample(struct thread *thread,
@@ -3114,14 +3118,19 @@ int machine__set_current_tid(struct machine *machine, int cpu, pid_t pid,
}
/*
- * Compares the raw arch string. N.B. see instead perf_env__arch() if a
- * normalized arch is needed.
+ * Compares the raw arch string. N.B. see instead perf_env__arch() or
+ * machine__normalize_is() if a normalized arch is needed.
*/
bool machine__is(struct machine *machine, const char *arch)
{
return machine && !strcmp(perf_env__raw_arch(machine->env), arch);
}
+bool machine__normalize_is(struct machine *machine, const char *arch)
+{
+ return machine && !strcmp(perf_env__arch(machine->env), arch);
+}
+
int machine__nr_cpus_avail(struct machine *machine)
{
return machine ? perf_env__nr_cpus_avail(machine->env) : 0;
diff --git a/tools/perf/util/machine.h b/tools/perf/util/machine.h
index a143087eeb47..665535153411 100644
--- a/tools/perf/util/machine.h
+++ b/tools/perf/util/machine.h
@@ -208,6 +208,7 @@ static inline bool machine__is_host(struct machine *machine)
}
bool machine__is(struct machine *machine, const char *arch);
+bool machine__normalize_is(struct machine *machine, const char *arch);
int machine__nr_cpus_avail(struct machine *machine);
struct thread *__machine__findnew_thread(struct machine *machine, pid_t pid, pid_t tid);
--
2.25.1
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