[PATCH][gdb/testsuite] Fix gdb.python/py-finish-breakpoint2.exp with -m32

[Tom de Vries]

Hi,

When running test-case gdb.python/py-finish-breakpoint2.exp with target board
unix/-m32, we run into:
...
(gdb) continue^M
Continuing.^M
Exception #10^M
^M
Breakpoint 3, throw_exception_1 (e=10) at py-finish-breakpoint2.cc:23^M
23        throw new int (e);^M
(gdb) FAIL: gdb.python/py-finish-breakpoint2.exp: \
  check FinishBreakpoint in catch()
...
With -m64, the test passes.

Relevant bit of the source:
...
    36    try
    37      {
    38        throw_exception_1 (10);
    39      }
    40    catch (const int *e)
    41      {
    42          std::cerr << "Exception #" << *e << std::endl;
    43      }
    44    i += 1; /* Break after exception 1.  */
...

The -m64 scenario in more detail:
- the test-case runs to throw_exception_1.
- it installs a FinishBreakpoint, which is a temporary breakpoint set at the
  return address of a frame.
- for -m64, that address is:
    400c47:       83 45 e4 01             addl   $0x1,-0x1c(%rbp)
  which corresponds the "i += 1 at line 44"
- the test-case then continues
- an exception is throw in throw_exection_1
- the exception is caught at line 40, and a message is printed
- line 44 is executed, and the FinishBreakpoint triggers.

With -m32, we have instead:
- the address where the finish breakpoint is set is:
    8048a0a:       83 c4 10                add    $0x10,%esp
  which is the lasn insn generated for the call at line 38
- the test-case continues
- an exception is throw in throw_exection_1
- consequently, the FinishBreakpoint is not triggered.

In conclusion, the test worked by accident for -m64, because the first insn
after the call to throw_exception_1 is also the first insn after the try.
And that just happens to be not the case for -m32.

Fix this by removing this part of the test.

Tested on x86_64-linux.

Any comments?

Thanks,
- Tom

[gdb/testsuite] Fix gdb.python/py-finish-breakpoint2.exp with -m32

gdb/testsuite/ChangeLog:

2021-01-18  Tom de Vries  <tdevries@suse.de>

	* gdb.python/py-finish-breakpoint2.exp: Remove part of test that
	works by accident.

---
 gdb/testsuite/gdb.python/py-finish-breakpoint2.exp | 6 ------
 1 file changed, 6 deletions(-)

diff --git a/gdb/testsuite/gdb.python/py-finish-breakpoint2.exp b/gdb/testsuite/gdb.python/py-finish-breakpoint2.exp
index 10c4b6e81b8..4193f073996 100644
--- a/gdb/testsuite/gdb.python/py-finish-breakpoint2.exp
+++ b/gdb/testsuite/gdb.python/py-finish-breakpoint2.exp
@@ -46,12 +46,6 @@ gdb_test "source $pyfile" ".*Python script imported.*" \
          
 gdb_breakpoint "throw_exception_1"
 gdb_test "continue" "Breakpoint .*throw_exception_1.*" "run to exception 1"
-
-gdb_test "python print (len(gdb.breakpoints()))" "3" "check BP count"
-gdb_test "python ExceptionFinishBreakpoint(gdb.newest_frame())" "init ExceptionFinishBreakpoint" "set FinishBP after the exception"
-gdb_test "continue" ".*stopped at ExceptionFinishBreakpoint.*" "check FinishBreakpoint in catch()"
-gdb_test "python print (len(gdb.breakpoints()))" "3" "check finish BP removal"
-
 gdb_test "continue" ".*Breakpoint.* throw_exception_1.*" "continue to second exception"
 gdb_test "python ExceptionFinishBreakpoint(gdb.newest_frame())" "init ExceptionFinishBreakpoint" "set FinishBP after the exception"
 gdb_test "continue" ".*exception did not finish.*" "FinishBreakpoint with exception thrown not caught"