linux-kernel - [PATCH] Fix jump parsing for C++ code.

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Message-ID: <13e1a405-edf9-e4c2-4327-a9b454353730@suse.cz>
Date:   Thu, 11 Feb 2021 13:37:55 +0100
From:   Martin Liška <mliska@...e.cz>
To:     linux-kernel@...r.kernel.org
Cc:     Jiri Slaby <jslaby@...e.cz>, linux-perf-users@...r.kernel.org
Subject: [PATCH] Fix jump parsing for C++ code.

Considering the following testcase:

int
foo(int a, int b)
{
   for (unsigned i = 0; i < 1000000000; i++)
     a += b;
   return a;
}

int main()
{
   foo (3, 4);
   return 0;
}

perf annotate displays:
  86.52 │40055e: → ja   40056c <foo(int, int)+0x26>
  13.37 │400560:   mov  -0x18(%rbp),%eax
        │400563:   add  %eax,-0x14(%rbp)
        │400566:   addl $0x1,-0x4(%rbp)
   0.11 │40056a: → jmp  400557 <foo(int, int)+0x11>
        │40056c:   mov  -0x14(%rbp),%eax
        │40056f:   pop  %rbp

and the 'ja 40056c' does not link to the location in the function.
It's caused by fact that comma is wrongly parsed, it's part
of function signature.

With my patch I see:

  86.52 │   ┌──ja   26
  13.37 │   │  mov  -0x18(%rbp),%eax
        │   │  add  %eax,-0x14(%rbp)
        │   │  addl $0x1,-0x4(%rbp)
   0.11 │   │↑ jmp  11
        │26:└─→mov  -0x14(%rbp),%eax

and 'o' output prints:
  86.52 │4005┌── ↓ ja   40056c <foo(int, int)+0x26>
  13.37 │4005│0:   mov  -0x18(%rbp),%eax
        │4005│3:   add  %eax,-0x14(%rbp)
        │4005│6:   addl $0x1,-0x4(%rbp)
   0.11 │4005│a: ↑ jmp  400557 <foo(int, int)+0x11>
        │4005└─→   mov  -0x14(%rbp),%eax

On the contrary, compiling the very same file with gcc -x c, the parsing
is fine because function arguments are not displyed:

jmp  400543 <foo+0x1d>

Signed-off-by: Martin Liška <mliska@...e.cz>
---
  tools/perf/util/annotate.c | 6 ++++++
  tools/perf/util/annotate.h | 1 +
  2 files changed, 7 insertions(+)

diff --git a/tools/perf/util/annotate.c b/tools/perf/util/annotate.c
index ce8c07bc8c56..e3eae646be3e 100644
--- a/tools/perf/util/annotate.c
+++ b/tools/perf/util/annotate.c
@@ -321,11 +321,16 @@ bool ins__is_call(const struct ins *ins)
  /*
   * Prevents from matching commas in the comment section, e.g.:
   * ffff200008446e70:       b.cs    ffff2000084470f4 <generic_exec_single+0x314>  // b.hs, b.nlast
+ *
+ * and skip comma as part of function arguments, e.g.:
+ * 1d8b4ac <linemap_lookup(line_maps const*, unsigned int)+0xcc>
   */
  static inline const char *validate_comma(const char *c, struct ins_operands *ops)
  {
  	if (ops->raw_comment && c > ops->raw_comment)
  		return NULL;
+	else if (ops->raw_func_start && c > ops->raw_func_start)
+		return NULL;
  
  	return c;
  }
@@ -341,6 +346,7 @@ static int jump__parse(struct arch *arch, struct ins_operands *ops, struct map_s
  	u64 start, end;
  
  	ops->raw_comment = strchr(ops->raw, arch->objdump.comment_char);
+	ops->raw_func_start = strchr(ops->raw, '<');
  	c = validate_comma(c, ops);
  
  	/*
diff --git a/tools/perf/util/annotate.h b/tools/perf/util/annotate.h
index 0a0cd4f32175..096cdaf21b01 100644
--- a/tools/perf/util/annotate.h
+++ b/tools/perf/util/annotate.h
@@ -32,6 +32,7 @@ struct ins {
  struct ins_operands {
  	char	*raw;
  	char	*raw_comment;
+	char	*raw_func_start;
  	struct {
  		char	*raw;
  		char	*name;
-- 
2.30.0