Re: [PATCH v2 4/4] perf tools: determine if LR is the return address

[Alexandre Truong]

Hi,

This patch is supposed to be a v3, I did a rebase.

Thanks,

Alexandre

On 2/12/21 5:03 PM, Alexandre Truong wrote:
> 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@xxxxxxx>
> ---
>   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,
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