[PATCH] [gdb/testsuite] Fix gdb.base/inline-frame-cycle-unwind.exp for s390x

[Kevin Buettner <kevinb@redhat.com>]

This commit fixes six failures for s390x due to a fundamental
difference in unwinding behavior between s390x and other
architectures:

FAIL: gdb.base/inline-frame-cycle-unwind.exp: bt: cycle at level 5:
  backtrace when the unwind is broken at frame 5
FAIL: gdb.base/inline-frame-cycle-unwind.exp: bt: cycle at level 3:
  backtrace when the unwind is broken at frame 3
FAIL: gdb.base/inline-frame-cycle-unwind.exp: bt: cycle at level 1:
  backtrace when the unwind is broken at frame 1
FAIL: gdb.base/inline-frame-cycle-unwind.exp: bt -no-filters: cycle at level 5:
  backtrace when the unwind is broken at frame 5
FAIL: gdb.base/inline-frame-cycle-unwind.exp: bt -no-filters: cycle at level 3:
  backtrace when the unwind is broken at frame 3
FAIL: gdb.base/inline-frame-cycle-unwind.exp: bt -no-filters: cycle at level 1:
  backtrace when the unwind is broken at frame 1

The core issue is that on s390x, the Canonical Frame Address (CFA) for
a function points *into the caller's stack frame*, whereas on x86_64
or aarch64 the CFA points *within the current function's frame*.  This
architectural difference causes cycle detection to occur later on
s390x.

The patch resolves this by:
- Making expected backtrace output architecture-specific.
- For non-s390x targets: expecting the full set of frames up to the
  specified level.
- For s390x: expecting fewer frames before detecting the cycle
  (e.g., level 5 shows 3 frames instead of 5).
- Skipping the cycle at level 1 test entirely on s390x since it cannot
  be detected at that frame.

Tested using recent Fedora releases on s390x, x86_64, and aarch64.
---
 .../gdb.base/inline-frame-cycle-unwind.exp    | 81 +++++++++++++------
 1 file changed, 57 insertions(+), 24 deletions(-)

diff --git a/gdb/testsuite/gdb.base/inline-frame-cycle-unwind.exp b/gdb/testsuite/gdb.base/inline-frame-cycle-unwind.exp
index 7fc47af624f..ccd86eb79ab 100644
--- a/gdb/testsuite/gdb.base/inline-frame-cycle-unwind.exp
+++ b/gdb/testsuite/gdb.base/inline-frame-cycle-unwind.exp
@@ -92,15 +92,31 @@ foreach bt_cmd { "bt" "bt -no-filters" } {
 	    gdb_test_no_output "python stop_at_level=5"
 	    gdb_test "maint flush register-cache" \
 		"Register cache flushed\\."
+
+	    # Frames expected on all targets
+	    set exp [list \
+		"#0 \[^\r\n\]* inline_func \\(\\) at \[^\r\n\]*" \
+		"#1 \[^\r\n\]* normal_func \\(\\) at \[^\r\n\]*" \
+		"#2 \[^\r\n\]* inline_func \\(\\) at \[^\r\n\]*" \
+		"#3 \[^\r\n\]* normal_func \\(\\) at \[^\r\n\]*"]
+
+	    # Additional frames required on non-s390x targets
+	    if {![istarget "s390x*-*-*"]} {
+		lappend exp \
+		    "#4 \[^\r\n\]* inline_func \\(\\) at \[^\r\n\]*" \
+		    "#5 \[^\r\n\]* normal_func \\(\\) at \[^\r\n\]*"
+	    }
+	    #
+	    # The final line that should appear for every target
+	    lappend exp \
+		"Backtrace stopped: previous frame identical to this frame \\(corrupt stack\\?\\)"
+
+	    # Convert the list to the single string that gdb_test_lines expects.
+	    # (This is equivalent to [multi_line {*}$exp]).
+	    set expected [join $exp "\r\n"]
+
 	    gdb_test_lines "$bt_cmd" "backtrace when the unwind is broken at frame 5" \
-		[multi_line \
-		    "#0 \[^\r\n\]* inline_func \\(\\) at \[^\r\n\]+" \
-		    "#1 \[^\r\n\]* normal_func \\(\\) at \[^\r\n\]+" \
-		    "#2 \[^\r\n\]* inline_func \\(\\) at \[^\r\n\]+" \
-		    "#3 \[^\r\n\]* normal_func \\(\\) at \[^\r\n\]+" \
-		    "#4 \[^\r\n\]* inline_func \\(\\) at \[^\r\n\]+" \
-		    "#5 \[^\r\n\]* normal_func \\(\\) at \[^\r\n\]+" \
-		    "Backtrace stopped: previous frame identical to this frame \\(corrupt stack\\?\\)"]
+		$expected
 	}
 
 	with_test_prefix "cycle at level 3" {
@@ -108,25 +124,42 @@ foreach bt_cmd { "bt" "bt -no-filters" } {
 	    gdb_test_no_output "python stop_at_level=3"
 	    gdb_test "maint flush register-cache" \
 		"Register cache flushed\\."
+	    # Frames expected on all targets
+	    set exp [list \
+		"#0 \[^\r\n\]* inline_func \\(\\) at \[^\r\n\]*" \
+		"#1 \[^\r\n\]* normal_func \\(\\) at \[^\r\n\]*"]
+
+	    # Additional frames required on non-s390x targets
+	    if {![istarget "s390x*-*-*"]} {
+		lappend exp \
+		    "#2 \[^\r\n\]* inline_func \\(\\) at \[^\r\n\]*" \
+		    "#3 \[^\r\n\]* normal_func \\(\\) at \[^\r\n\]*"
+	    }
+	    #
+	    # The final line that should appear for every target
+	    lappend exp \
+		"Backtrace stopped: previous frame identical to this frame \\(corrupt stack\\?\\)"
+
+	    # Convert the list to the single string that gdb_test_lines expects.
+	    # (This is equivalent to [multi_line {*}$exp]).
+	    set expected [join $exp "\r\n"]
+
 	    gdb_test_lines "$bt_cmd" "backtrace when the unwind is broken at frame 3" \
-		[multi_line \
-		    "#0 \[^\r\n\]* inline_func \\(\\) at \[^\r\n\]+" \
-		    "#1 \[^\r\n\]* normal_func \\(\\) at \[^\r\n\]+" \
-		    "#2 \[^\r\n\]* inline_func \\(\\) at \[^\r\n\]+" \
-		    "#3 \[^\r\n\]* normal_func \\(\\) at \[^\r\n\]+" \
-		    "Backtrace stopped: previous frame identical to this frame \\(corrupt stack\\?\\)"]
+		$expected
 	}
 
-	with_test_prefix "cycle at level 1" {
-	    # Arrange to introduce a stack cycle at frame 1.
-	    gdb_test_no_output "python stop_at_level=1"
-	    gdb_test "maint flush register-cache" \
-		"Register cache flushed\\."
-	    gdb_test_lines "$bt_cmd" "backtrace when the unwind is broken at frame 1" \
-		[multi_line \
-		    "#0 \[^\r\n\]* inline_func \\(\\) at \[^\r\n\]+" \
-		    "#1 \[^\r\n\]* normal_func \\(\\) at \[^\r\n\]+" \
-		    "Backtrace stopped: previous frame identical to this frame \\(corrupt stack\\?\\)"]
+	if {![istarget "s390x*-*-*"]} {
+	    with_test_prefix "cycle at level 1" {
+		# Arrange to introduce a stack cycle at frame 1.
+		gdb_test_no_output "python stop_at_level=1"
+		gdb_test "maint flush register-cache" \
+		    "Register cache flushed\\."
+		gdb_test_lines "$bt_cmd" "backtrace when the unwind is broken at frame 1" \
+		    [multi_line \
+			"#0 \[^\r\n\]* inline_func \\(\\) at \[^\r\n\]+" \
+			"#1 \[^\r\n\]* normal_func \\(\\) at \[^\r\n\]+" \
+			"Backtrace stopped: previous frame identical to this frame \\(corrupt stack\\?\\)"]
+	    }
 	}
 
 	# Flush the register cache (which also flushes the frame cache) so we
-- 
2.51.0