[PATCH] [gdb/testsuite] Fix gdb.python/py-finish-breakpoint-tailcall.exp with gcc 16

[Tom de Vries <tdevries@suse.de>]

On openSUSE Leap 16.0, with gcc 15.3.0, for test-case
gdb.python/py-finish-breakpoint-tailcall.exp I get:
...
(gdb) python MyFinishBreakpoint(frame)
Temporary breakpoint 2 at 0x40102a: file py-finish-breakpoint-tailcall.c, \
  line 43.
(gdb) PASS: $exp: parent_frame=true: create finish breakpoint
...

And on openSUSE Tumbleweed, with gcc 16.1.1 I get instead:
...
(gdb) python MyFinishBreakpoint(frame)
Temporary breakpoint 2 at 0x40102a: file py-finish-breakpoint-tailcall.c, \
   line 44.
(gdb) FAIL: $exp: parent_frame=true: create finish breakpoint
...

The only difference is in the line numbers, 43 and 44, both in main:
...
    39	int
    40	main (void)
    41	{
    42	  int result = tailcall_function (42);
    43	  result -= global_var;  /* Temporary breakpoint here.  */
    44	  return result;
    45	}
...

The executable is compiled with O2, and the code for main is different.

With gcc 15, we have:
...
0000000000401020 <main>:
  401020:       bf 2a 00 00 00          mov    $0x2a,%edi
  401025:       e8 26 01 00 00          call   401150 <tailcall_function>
  40102a:       8b 15 e0 2f 00 00       mov    0x2fe0(%rip),%edx
  401030:       29 d0                   sub    %edx,%eax
  401032:       c3                      ret
...
and the line number associated with 0x40102a, the first instruction after the
call is 43:
...
File name                        Line number  Starting address    View    Stmt
py-finish-breakpoint-tailcall.c           43          0x40102a               x
...

With gcc 16, the mov and sub have been merged:
...
0000000000401020 <main>:
  401020:       bf 2a 00 00 00          mov    $0x2a,%edi
  401025:       e8 26 01 00 00          call   401150 <tailcall_function>
  40102a:       2b 05 e0 2f 00 00       sub    0x2fe0(%rip),%eax
  401030:       c3                      ret
...
and the line number info is different:
...
File name                        Line number  Starting address    View    Stmt
py-finish-breakpoint-tailcall.c           43          0x40102a               x
py-finish-breakpoint-tailcall.c           44          0x40102a       1       x
py-finish-breakpoint-tailcall.c           43          0x40102a       2
...
and gdb picks 44 in this case.

Fix this by merging lines 43 and 44 in the test-case:
...
-  result -= global_var;  /* Temporary breakpoint here.  */
-  return result;
+  return result - global_var;  /* Temporary breakpoint here.  */
...

Tested on x86_64-linux.

I've also verified that reverting the fix in commit e6bdfed6f5d ("gdb: fix
frame_unwind_caller_WHAT functions for inline and tail calls"), the commit
that introduced the test-case still makes the test-case fail.

Bug: https://sourceware.org/bugzilla/show_bug.cgi?id=33989
---
 gdb/testsuite/gdb.python/py-finish-breakpoint-tailcall.c | 3 +--
 1 file changed, 1 insertion(+), 2 deletions(-)

diff --git a/gdb/testsuite/gdb.python/py-finish-breakpoint-tailcall.c b/gdb/testsuite/gdb.python/py-finish-breakpoint-tailcall.c
index d129d7e41b4..844ac1d2ea6 100644
--- a/gdb/testsuite/gdb.python/py-finish-breakpoint-tailcall.c
+++ b/gdb/testsuite/gdb.python/py-finish-breakpoint-tailcall.c
@@ -40,6 +40,5 @@ int
 main (void)
 {
   int result = tailcall_function (42);
-  result -= global_var;			/* Temporary breakpoint here.  */
-  return result;
+  return result - global_var;			/* Temporary breakpoint here.  */
 }

base-commit: 6d1be0b90e837e4c82eaaf6f9e8c7da7227902e1
-- 
2.51.0