[gdb/testsuite] Fix gdb.base/branch-to-self.exp on arm-linux

On arm-linux (ubuntu 24.04 with gcc 13.3.0) with target board unix/-marm and
test-case gdb.base/branch-to-self.exp I run into:
...
(gdb) continue^M
Continuing.^M
^M
Breakpoint 2, main () at branch-to-self.c:38^M
38        for (;;); /* loop-line */^M
(gdb) PASS: $exp: single-step: continue to breakpoint: hit breakpoint
si^M
0x0040058c      38        for (;;); /* loop-line */^M
(gdb) FAIL: $exp: single-step: si
...

In contrast, on the same machine but with debian testing and gcc 14.2.0 we have:
...
(gdb) continue^M
Continuing.^M
^M
Breakpoint 2, main () at branch-to-self.c:38^M
38        for (;;); /* loop-line */^M
(gdb) PASS: $exp: single-step: continue to breakpoint: hit breakpoint
si^M
^M
Breakpoint 2, main () at branch-to-self.c:38^M
38        for (;;); /* loop-line */^M
(gdb) PASS: $exp: single-step: stepi
...

The difference is in the instruction(s) generated for the loop.

In the passing case, we have:
...
 588:   eafffffe        b       588 <main+0x24>
...
and in the failing case:
...
 588:   e320f000        nop     {0}
 58c:   eafffffd        b       588 <main+0x24>
...

The purpose of this part of the test-case is to:
- generate a branch instruction that jumps to itself, and
- set a breakpoint on it, and check that stepi-ing from that breakpoint
  triggers the breakpoint again.

As we can see, in the failing case we failed to generate a branch instruction
that jumps to itself, and consequently we cannot expect to hit the breakpoint
again after issuing a single si.

Fix this by issuing stepi until we hit the breakpoint.

Tested on arm-linux.

Reviewed-by: Thiago Jung Bauermann <thiago.bauermann@linaro.org>

1 files changed, 16 insertions, 1 deletions

diff --git a/gdb/testsuite/gdb.base/branch-to-self.exp b/gdb/testsuite/gdb.base/branch-to-self.exp
index 9b4f746..71859d7 100644
--- a/gdb/testsuite/gdb.base/branch-to-self.exp
+++ b/gdb/testsuite/gdb.base/branch-to-self.exp
@@ -35,7 +35,22 @@ with_test_prefix "single-step" {
     gdb_test "break ${testfile}.c:${line_num}" "Breakpoint .*" \
 	"set breakpoint"
     gdb_continue_to_breakpoint "hit breakpoint"
-    gdb_test "si" ".*${testfile}.c:${line_num}.*"
+
+    set stepi_count 1
+    gdb_test_multiple "stepi" "" {
+	-re -wrap ".*${testfile}.c:${line_num}.*" {
+	    pass $gdb_test_name
+	}
+	-re -wrap "" {
+	    if { $stepi_count == 10 } {
+		fail $gdb_test_name
+	    } else {
+		incr stepi_count
+		send_gdb "stepi\n"
+		exp_continue
+	    }
+	}
+    }
 }
 
 with_test_prefix "break-cond" {