Re: [PATCH] testsuite: ada-valprint-error relocation issue

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

On 4/1/26 12:33 PM, Bratislav Filipovic wrote:
> The ada-valprint-error.exp test links a nodebug .o file with a separate
> DWARF .o file generated by lib/dwarf.exp. This requires the linker to
> apply relocations for initialized pointers in the .data section.
> 
> Some clang + linker combinations fail to apply these relocations,
> leaving fd__global as NULL instead of pointing to buffer. This causes
> the test to print null instead of the expected error message.
> 
> Binary evidence from .comment section confirms which compiler and
> linker were used. Testing shows:
> - GCC 13 + GNU ld 2.42: PASS
> - clang 20 + GNU ld 2.42: FAIL
> - clang 22 + ld.lld 22: FAIL
> - clang 17/19 + GNU ld 2.45.0: PASS
> 
> The failure is a linker limitation when handling this specific
> relocation pattern, not a GDB bug. Document this in the test file
> to help users understand why the test may fail with certain toolchains.
> ---
> Thanks for review Tom. I changed it per your suggestions. It seems to
> fail only for some combinations of clang + linker.
> 

Hi,

thanks for the update, I have a few comments.

First of all, the commit needs whitespace fixes, as mentioned by the 
pre-commit check:
...
$ pre-commit run --all-files check-whitespace
check-whitespace.........................................................Failed
- hook id: check-whitespace
- exit code: 2

gdb/testsuite/gdb.dwarf2/ada-valprint-error.exp:119: indent with spaces.
+        unsupported "linker failed to apply relocation for fd__global"
gdb/testsuite/gdb.dwarf2/ada-valprint-error.exp:120: indent with spaces.
+        return
gdb/testsuite/gdb.dwarf2/ada-valprint-error.exp:123: indent with spaces.
+        pass $gdb_test_name

$
...

[ Consider installing pre-commit on your system (to be able to run it 
manually), and also installing pre-commit hooks in your git repo (to let 
git run it automatically). ]

>   gdb/testsuite/gdb.dwarf2/ada-valprint-error.exp | 17 +++++++++++++++++
>   1 file changed, 17 insertions(+)
> 
> diff --git a/gdb/testsuite/gdb.dwarf2/ada-valprint-error.exp b/gdb/testsuite/gdb.dwarf2/ada-valprint-error.exp
> index f3d61e91..b72682f7 100644
> --- a/gdb/testsuite/gdb.dwarf2/ada-valprint-error.exp
> +++ b/gdb/testsuite/gdb.dwarf2/ada-valprint-error.exp
> @@ -107,6 +107,23 @@ if { [prepare_for_testing ${testfile}.exp ${testfile} \
>       return -1
>   }
>   
> +# Note: This test may fail with certain clang + linker combinations
> +# Specifically, clang + ld.lld can fail to apply relocations when linking
> +# nodebug .o with separate DWARF .o, leaving fd__global as NULL instead
> +# of pointing to buffer. The failure is a linker limitation, not a GDB bug.
> +#
> +# Known to fail: clang 20/22 + GNU ld 2.42, clang 22 + ld.lld 22
> +# Known to pass: GCC + GNU ld, clang 17/19 + GNU ld 2.45.0
> +gdb_test_multiple "print /x fd__global" "check fd__global value" {
> +    -re -wrap "@0x0: 0x0" {
> +        unsupported "linker failed to apply relocation for fd__global"
> +        return
> +    }

FWIW, I usually try to keep non-local Tcl control flow (like return or 
break/continue not contained in a local loop) out of the regexp clauses. 
  I think this may have been necessary at some point, so I got in the 
habit of doing so.  I'm not sure if that's still necessary, but I still 
think it's a somewhat cleaner style.

The pattern I use instead is:
...
set unsupported 0
gdb_test_multiple ... {
     -re -wrap ... {
	set unsupported 1
     }
     ...
}
if {$unsupported} {
     unsupported "linker failed to apply relocation for fd__global"
     return
}
...

Anyway, it's not necessary to change this.

> +    -re -wrap "= $hex" {
> +        pass $gdb_test_name
> +    }
> +}
> +

I applied the patch, ran the test-case, and ran into:
...
(gdb) print /x fd__global^M
$1 = (fd__ints_doubled &) @0x404020: 0x404020 <buffer>^M
(gdb) FAIL: gdb.dwarf2/ada-valprint-error.exp: check fd__global value
...

The regexp doesn't match.

This can easily be fixed by simply using:
...
     -re -wrap "" {
         pass $gdb_test_name
     }
...

Thanks,
- Tom

>   gdb_test_no_output "set language ada"
>   
>   gdb_test "print fd.global" \