Em Tue, Sep 28, 2021 at 10:39:05PM +0200, Mark Wielaard escreveu:

Hi,

On Tue, Sep 28, 2021 at 09:52:53PM +0200, Jiri Olsa wrote:

quoted

Got following build fail on powerpc:

    CC      arch/powerpc/util/skip-callchain-idx.o
  In function ‘check_return_reg’,
      inlined from ‘check_return_addr’ at arch/powerpc/util/skip-callchain-idx.c:213:7,
      inlined from ‘arch_skip_callchain_idx’ at arch/powerpc/util/skip-callchain-idx.c:265:7:
  arch/powerpc/util/skip-callchain-idx.c:54:18: error: ‘dwarf_frame_register’ accessing 96 bytes \
  in a region of size 64 [-Werror=stringop-overflow=]
     54 |         result = dwarf_frame_register(frame, ra_regno, ops_mem, &ops, &nops);
        |                  ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
  arch/powerpc/util/skip-callchain-idx.c: In function ‘arch_skip_callchain_idx’:
  arch/powerpc/util/skip-callchain-idx.c:54:18: note: referencing argument 3 of type ‘Dwarf_Op *’
  In file included from /usr/include/elfutils/libdwfl.h:32,
                   from arch/powerpc/util/skip-callchain-idx.c:10:
  /usr/include/elfutils/libdw.h:1069:12: note: in a call to function ‘dwarf_frame_register’
   1069 | extern int dwarf_frame_register (Dwarf_Frame *frame, int regno,
        |            ^~~~~~~~~~~~~~~~~~~~
  cc1: all warnings being treated as errors

The dwarf_frame_register args changed with [1],
Updating ops_mem accordingly.

[1] https://sourceware.org/git/?p=elfutils.git;a=commit;h=5621fe5443da23112170235dd5cac161e5c75e65

The warning (new with GCC11) and the fix are correct.

I'm taking this as an Acked-by, ok?

- Arnaldo
 

The code probably worked fine before because the next var on the stack
was the dummy Dwarf_Op which would have been as if the ops_mem[2] was
actually ops_mem[3] already. You don't need the dummy var now and
Dwarf_Op *ops doesn't need to be initialized (the dwarf_frame_register
will initialize it).

Note that [1] didn't change the args of the dwarf_frame_register, but
did fix a similar bug in one of the elfutils own tests (and updated
the comment on the function to hopefully be more clear).

Cheers,

Mark

quoted

Cc: Mark Wielaard <redacted>
Cc: Sukadev Bhattiprolu <redacted>
Signed-off-by: Jiri Olsa <redacted>
---
 tools/perf/arch/powerpc/util/skip-callchain-idx.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/tools/perf/arch/powerpc/util/skip-callchain-idx.c b/tools/perf/arch/powerpc/util/skip-callchain-idx.c
index 3018a054526a..20cd6244863b 100644
--- a/tools/perf/arch/powerpc/util/skip-callchain-idx.c
+++ b/tools/perf/arch/powerpc/util/skip-callchain-idx.c

@@ -45,7 +45,7 @@ static const Dwfl_Callbacks offline_callbacks = {
  */
 static int check_return_reg(int ra_regno, Dwarf_Frame *frame)
 {
-	Dwarf_Op ops_mem[2];
+	Dwarf_Op ops_mem[3];
 	Dwarf_Op dummy;
 	Dwarf_Op *ops = &dummy;
 	size_t nops;

-- 
2.31.1

-- 

- Arnaldo