[Bug breakpoints/26096] New: gdb sets breakpoint at cold clone

["vries at gcc dot gnu.org" <sourceware-bugzilla@sourceware.org>]

https://sourceware.org/bugzilla/show_bug.cgi?id=26096

            Bug ID: 26096
           Summary: gdb sets breakpoint at cold clone
           Product: gdb
           Version: HEAD
            Status: NEW
          Severity: normal
          Priority: P2
         Component: breakpoints
          Assignee: unassigned at sourceware dot org
          Reporter: vries at gcc dot gnu.org
  Target Milestone: ---

Consider test-case test.c:
...
$ cat test.c
#include <stdlib.h>

int a;
int b;
int c;

static int __attribute__((used, noinline, noclone))
foo (void)
{
  a = 2;
  if (b)
    abort ();

  return c;
}

static int __attribute__((used, noinline, noclone))
bar (void)
{
  a = 1;
  if (c)
    abort ();
  return b;
}

int
main (int argc, char **)
{
  b = argc * 2;
  c = argc / 2;

  if (b + c == 5)
    abort ();

  return foo () + bar ();
}
...

Compiled with gcc-10:
...
$ g++-10 test.c -O2 -g  -Wall -Wextra
...

The functions foo and bar get split into a hot and cold part by gcc's
freorder-blocks-and-partition:
...
$ nm a.out | c++filt | egrep "foo|bar"
00000000004005b0 t bar()
0000000000400455 t bar() [clone .cold]
0000000000400580 t foo()
0000000000400450 t foo() [clone .cold]
...

When we set breakpoints on foo and bar however, we get two breakpoint locations
per function:
...
$ gdb -batch a.out -ex "b foo" -ex "b bar" -ex "info break"
Breakpoint 1 at 0x400450: foo. (2 locations)
Breakpoint 2 at 0x400455: bar. (2 locations)
Num     Type           Disp Enb Address            What
1       breakpoint     keep y   <MULTIPLE>         
1.1                         y   0x0000000000400450 in foo() at test.c:12
1.2                         y   0x0000000000400580 in foo() at test.c:10
2       breakpoint     keep y   <MULTIPLE>         
2.1                         y   0x0000000000400455 in bar() at test.c:22
2.2                         y   0x00000000004005b0 in bar() at test.c:20
...

So, the cold part of the function gets its own breakpoint.

In other words, we have:
...
$ gdb -q a.out
Reading symbols from a.out...
(gdb) b foo
Breakpoint 1 at 0x400450: foo. (2 locations)
(gdb) r
Starting program: /home/vries/a.out 

Breakpoint 1, foo () at test.c:10
10        a = 2;
(gdb) c
Continuing.

Breakpoint 1, foo () at test.c:12
12          abort ();
...

-- 
You are receiving this mail because:
You are on the CC list for the bug.