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

[Kevin Buettner <kevinb@redhat.com>]

Ping.

On Sat,  1 Nov 2025 21:46:51 -0700
Kevin Buettner <kevinb@redhat.com> wrote:

> 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
>