linux-kernel - [PATCH] perf test: Fix signal test inline assembly

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Message-Id: <20200911130005.1842138-1-jolsa@kernel.org>
Date:   Fri, 11 Sep 2020 15:00:05 +0200
From:   Jiri Olsa <jolsa@...nel.org>
To:     Arnaldo Carvalho de Melo <acme@...nel.org>
Cc:     Wang Nan <wangnan0@...wei.com>,
        lkml <linux-kernel@...r.kernel.org>,
        Peter Zijlstra <a.p.zijlstra@...llo.nl>,
        Ingo Molnar <mingo@...nel.org>,
        Namhyung Kim <namhyung@...nel.org>,
        Alexander Shishkin <alexander.shishkin@...ux.intel.com>,
        Michael Petlan <mpetlan@...hat.com>
Subject: [PATCH] perf test: Fix signal test inline assembly

When compiling with DEBUG=1 on Fedora 32 I'm getting crash for
'perf test signal':

  Program received signal SIGSEGV, Segmentation fault.
  0x0000000000c68548 in __test_function ()
  (gdb) bt
  #0  0x0000000000c68548 in __test_function ()
  #1  0x00000000004d62e9 in test_function () at tests/bp_signal.c:61
  #2  0x00000000004d689a in test__bp_signal (test=0xa8e280 <generic_ ...
  #3  0x00000000004b7d49 in run_test (test=0xa8e280 <generic_tests+1 ...
  #4  0x00000000004b7e7f in test_and_print (t=0xa8e280 <generic_test ...
  #5  0x00000000004b8927 in __cmd_test (argc=1, argv=0x7fffffffdce0, ...
  ...

It's caused by __test_function being in .bss section:

  $ readelf -a ./perf | less
    [Nr] Name              Type             Address           Offset
         Size              EntSize          Flags  Link  Info  Align
    ...
    [28] .bss              NOBITS           0000000000c356a0  008346a0
         00000000000511f8  0000000000000000  WA       0     0     32

  $ nm perf | grep __test_function
  0000000000c68548 B __test_function

I guess most of the time we're just lucky the inline asm ended up
in .text section, so making it specific explicit with push and pop
section cluases.

  $ readelf -a ./perf | less
    [Nr] Name              Type             Address           Offset
         Size              EntSize          Flags  Link  Info  Align
    ...
    [13] .text             PROGBITS         0000000000431240  00031240
         0000000000306faa  0000000000000000  AX       0     0     16

  $ nm perf | grep __test_function
  00000000004d62c8 T __test_function

Cc: Wang Nan <wangnan0@...wei.com>
Fixes: 8fd34e1cce18 ("perf test: Improve bp_signal")
Signed-off-by: Jiri Olsa <jolsa@...nel.org>
---
 tools/perf/tests/bp_signal.c | 5 ++++-
 1 file changed, 4 insertions(+), 1 deletion(-)

diff --git a/tools/perf/tests/bp_signal.c b/tools/perf/tests/bp_signal.c
index da8ec1e8e064..cc9fbcedb364 100644
--- a/tools/perf/tests/bp_signal.c
+++ b/tools/perf/tests/bp_signal.c
@@ -45,10 +45,13 @@ volatile long the_var;
 #if defined (__x86_64__)
 extern void __test_function(volatile long *ptr);
 asm (
+	".pushsection .text;"
 	".globl __test_function\n"
+	".type __test_function, @function;"
 	"__test_function:\n"
 	"incq (%rdi)\n"
-	"ret\n");
+	"ret\n"
+	".popsection\n");
 #else
 static void __test_function(volatile long *ptr)
 {
-- 
2.26.2