perf arm64: Inject missing frames when using 'perf record --call-graph=fp'

When unwinding using frame pointers on ARM64, the return address of the
current function may not have been pushed into the stack when a function
was interrupted, which makes perf show an incorrect call graph to the
user.

Consider the following example program:

  void leaf() {
      /* long computation */
  }

  void parent() {
      // (1)
      leaf();
      // (2)
  }

  ... could be compiled into (using gcc -fno-inline -fno-omit-frame-pointer):

  leaf:
      /* long computation */
      nop
      ret
  parent:
      // (1)
      stp     x29, x30, [sp, -16]!
      mov     x29, sp
      bl      parent
      nop
      ldp     x29, x30, [sp], 16
      // (2)
      ret

If the program is interrupted at (1), (2), or any point in "leaf:", the
call graph will skip the callers of the current function. We can unwind
using the dwarf info and check if the return addr is the same as the LR
register, and inject the missing frame into the call graph.

Before this patch, the above example shows the following call-graph when
recording using "--call-graph fp" mode in ARM64:

  # Children      Self  Command   Shared Object     Symbol
  # ........  ........  ........  ................  ......................
  #
      99.86%    99.86%  program3  program3          [.] leaf
  	    |
  	    ---_start
  	       __libc_start_main
  	       main
  	       leaf

As can be seen, the "parent" function is missing. This is specially
problematic in "leaf" because for leaf functions the compiler may always
omit pushing the return addr into the stack. After this patch, it shows
the correct graph:

  # Children      Self  Command   Shared Object     Symbol
  # ........  ........  ........  ................  ......................
  #
      99.86%    99.86%  program3  program3          [.] leaf
  	    |
  	    ---_start
  	       __libc_start_main
  	       main
  	       parent
  	       leaf

Reviewed-by: James Clark <james.clark@arm.com>
Signed-off-by: Alexandre Truong <alexandre.truong@arm.com>
Acked-by: Jiri Olsa <jolsa@kernel.org>
Cc: Alexander Shishkin <alexander.shishkin@linux.intel.com>
Cc: John Garry <john.garry@huawei.com>
Cc: Leo Yan <leo.yan@linaro.org>
Cc: Mark Rutland <mark.rutland@arm.com>
Cc: Mathieu Poirier <mathieu.poirier@linaro.org>
Cc: Namhyung Kim <namhyung@kernel.org>
Cc: Will Deacon <will@kernel.org>
Cc: linux-arm-kernel@lists.infradead.org
Link: https://lore.kernel.org/r/20211217154521.80603-7-german.gomez@arm.com
Signed-off-by: German Gomez <german.gomez@arm.com>
[ Rename machine__normalize_is() to machine__normalized_is(), as suggested by James Clark ]
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>

1 files changed, 1 insertions, 0 deletions

diff --git a/tools/perf/util/machine.h b/tools/perf/util/machine.h
index a143087eeb47..c5a45dc8df4c 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__normalized_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);