Convert dw2-const.exp to use the DWARF assembler

  This patch converts dw2-const.exp to use the DWARF assembler rather
than a .S file.  The conversion was largely done using the script from
contrib.
---
 gdb/testsuite/gdb.dwarf2/dw2-const.S   | 256 -------------------------
 gdb/testsuite/gdb.dwarf2/dw2-const.exp |  52 ++++-
 2 files changed, 49 insertions(+), 259 deletions(-)
 delete mode 100644 gdb/testsuite/gdb.dwarf2/dw2-const.S


base-commit: 1678d7d3d2e4cf83cda5a96334a0326573ad0f7c
  

On 5/22/26 5:55 PM, Tom Tromey wrote:
> This patch converts dw2-const.exp to use the DWARF assembler rather
> than a .S file.  The conversion was largely done using the script from
> contrib.

Hi,

I reverse-applied "[gdb/testsuite] Complete 64-bit port of 
gdb.dwarf2/dw2-skip-prologue.exp", then applied this patch.

I ran the test-case, and it went fine.  I check for warnings with 
readelf and llvm-dwarfdump, and that was fine as well.

Then I ran it with target board unix/-m32, and ran into:
...
(gdb) print/x val8^M
$2 = 0x0^M
(gdb) FAIL: gdb.dwarf2/dw2-const.exp: print/x val8
...

Thanks,
- Tom

> ---
>   gdb/testsuite/gdb.dwarf2/dw2-const.S   | 256 -------------------------
>   gdb/testsuite/gdb.dwarf2/dw2-const.exp |  52 ++++-
>   2 files changed, 49 insertions(+), 259 deletions(-)
>   delete mode 100644 gdb/testsuite/gdb.dwarf2/dw2-const.S
> 
> diff --git a/gdb/testsuite/gdb.dwarf2/dw2-const.S b/gdb/testsuite/gdb.dwarf2/dw2-const.S
> deleted file mode 100644
> index 94cf1acbed6..00000000000
> --- a/gdb/testsuite/gdb.dwarf2/dw2-const.S
> +++ /dev/null
> @@ -1,256 +0,0 @@
> -/* This testcase is part of GDB, the GNU debugger.
> -
> -   Copyright 2010-2026 Free Software Foundation, Inc.
> -
> -   This program is free software; you can redistribute it and/or modify
> -   it under the terms of the GNU General Public License as published by
> -   the Free Software Foundation; either version 3 of the License, or
> -   (at your option) any later version.
> -
> -   This program is distributed in the hope that it will be useful,
> -   but WITHOUT ANY WARRANTY; without even the implied warranty of
> -   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
> -   GNU General Public License for more details.
> -
> -   You should have received a copy of the GNU General Public License
> -   along with this program.  If not, see <http://www.gnu.org/licenses/>.  */
> -
> -/* Dummy function to provide debug information for.  */
> -
> -	.text
> -.Lbegin_text1:
> -	.globl func_cu1
> -	.type func_cu1, %function
> -func_cu1:
> -.Lbegin_func_cu1:
> -	.int 0
> -.Lend_func_cu1:
> -	.size func_cu1, .-func_cu1
> -.Lend_text1:
> -
> -/* Debug information */
> -
> -	.section .debug_info
> -.Lcu1_begin:
> -	/* CU header */
> -	.4byte	.Lcu1_end - .Lcu1_start		/* Length of Compilation Unit */
> -.Lcu1_start:
> -	.2byte	2				/* DWARF Version */
> -	.4byte	.Labbrev1_begin			/* Offset into abbrev section */
> -	.byte	8				/* Pointer size */
> -
> -	/* CU die */
> -	.uleb128 1				/* Abbrev: DW_TAG_compile_unit */
> -	.4byte	.Lline1_begin			/* DW_AT_stmt_list */
> -	.ascii	"file1.txt\0"			/* DW_AT_name */
> -	.ascii	"GNU C 3.3.3\0"			/* DW_AT_producer */
> -	.byte	1				/* DW_AT_language (C) */
> -
> -        .uleb128        0x8                     /* Abbrev: DW_TAG_constant */
> -        .ascii          "twelve\0"              /* DW_AT_name */
> -	.4byte		.Ltype_const-.Lcu1_begin   /* DW_AT_type */
> -        .byte           0xc                     /* DW_AT_const_value */
> -
> -.Ltype_const:
> -        .uleb128        0x9                     /* Abbrev: DW_TAG_const_type */
> -        .4byte           .Ltype_int-.Lcu1_begin /* DW_AT_type */
> -
> -        .uleb128        0xa                     /* Abbrev: DW_TAG_variable */
> -        .ascii          "val8\0"                /* DW_AT_name */
> -        .4byte          .Ltype_const8-.Lcu1_begin   /* DW_AT_type */
> -        .byte           2f - 1f                 /* DW_AT_location */
> -1:      .byte           0x11                    /* DW_OP_consts */
> -#if 0 /* gas encodes it explicitly.  */
> -        .slab128        0xffffffff00000000
> -#endif
> -#if 0 /* gas encoded it correctly - formed GDB FAILed.  */
> -        .sleb128        -4294967296
> -#endif
> -#if 1 /* Rather encode sleb128 by hand.  */
> -        .byte           0x80, 0x80, 0x80, 0x80, 0x70
> -#endif
> -        .byte           0x9f                    /* DW_OP_stack_value */
> -2:
> -
> -.Ltype_const8:
> -        .uleb128        0x9                     /* Abbrev: DW_TAG_const_type */
> -        .4byte           .Ltype_int8-.Lcu1_begin /* DW_AT_type */
> -
> -	/* func_cu1 */
> -	.uleb128	2			/* Abbrev: DW_TAG_subprogram */
> -	.byte		1			/* DW_AT_external */
> -	.byte		1			/* DW_AT_decl_file */
> -	.byte		2			/* DW_AT_decl_line */
> -	.ascii		"func_cu1\0"		/* DW_AT_name */
> -	.4byte		.Ltype_int-.Lcu1_begin	/* DW_AT_type */
> -	.byte		1			/* DW_AT_frame_base: length */
> -	.byte		0x55			/* DW_AT_frame_base: DW_OP_reg5 */
> -
> -.Ltype_int:
> -	.uleb128	3			/* Abbrev: DW_TAG_base_type */
> -	.ascii		"int\0"			/* DW_AT_name */
> -	.byte		4			/* DW_AT_byte_size */
> -	.byte		5			/* DW_AT_encoding */
> -
> -.Ltype_int8:
> -	.uleb128	3			/* Abbrev: DW_TAG_base_type */
> -	.ascii		"int8\0"		/* DW_AT_name */
> -	.byte		8			/* DW_AT_byte_size */
> -	.byte		5			/* DW_AT_encoding */
> -
> -	.byte		0			/* End of children of CU */
> -
> -.Lcu1_end:
> -
> -/* Abbrev table */
> -	.section .debug_abbrev
> -.Labbrev1_begin:
> -	.uleb128	1			/* Abbrev code */
> -	.uleb128	0x11			/* DW_TAG_compile_unit */
> -	.byte		1			/* has_children */
> -	.uleb128	0x10			/* DW_AT_stmt_list */
> -	.uleb128	0x6			/* DW_FORM_data4 */
> -	.uleb128	0x3			/* DW_AT_name */
> -	.uleb128	0x8			/* DW_FORM_string */
> -	.uleb128	0x25			/* DW_AT_producer */
> -	.uleb128	0x8			/* DW_FORM_string */
> -	.uleb128	0x13			/* DW_AT_language */
> -	.uleb128	0xb			/* DW_FORM_data1 */
> -	.byte		0x0			/* Terminator */
> -	.byte		0x0			/* Terminator */
> -
> -	.uleb128	2			/* Abbrev code */
> -	.uleb128	0x2e			/* DW_TAG_subprogram */
> -	.byte		0			/* has_children */
> -	.uleb128	0x3f			/* DW_AT_external */
> -	.uleb128	0xc			/* DW_FORM_flag */
> -	.uleb128	0x3a			/* DW_AT_decl_file */
> -	.uleb128	0xb			/* DW_FORM_data1 */
> -	.uleb128	0x3b			/* DW_AT_decl_line */
> -	.uleb128	0xb			/* DW_FORM_data1 */
> -	.uleb128	0x3			/* DW_AT_name */
> -	.uleb128	0x8			/* DW_FORM_string */
> -	.uleb128	0x49			/* DW_AT_type */
> -	.uleb128	0x13			/* DW_FORM_ref4 */
> -	.uleb128	0x40			/* DW_AT_frame_base */
> -	.uleb128	0xa			/* DW_FORM_block1 */
> -	.byte		0x0			/* Terminator */
> -	.byte		0x0			/* Terminator */
> -
> -	.uleb128	3			/* Abbrev code */
> -	.uleb128	0x24			/* DW_TAG_base_type */
> -	.byte		0			/* has_children */
> -	.uleb128	0x3			/* DW_AT_name */
> -	.uleb128	0x8			/* DW_FORM_string */
> -	.uleb128	0xb			/* DW_AT_byte_size */
> -	.uleb128	0xb			/* DW_FORM_data1 */
> -	.uleb128	0x3e			/* DW_AT_encoding */
> -	.uleb128	0xb			/* DW_FORM_data1 */
> -	.byte		0x0			/* Terminator */
> -	.byte		0x0			/* Terminator */
> -
> -        .uleb128        0x8                     /* abbrev code */
> -        .uleb128        0x27                    /* TAG: DW_TAG_constant */
> -        .byte           0x0                     /* DW_children_no */
> -        .uleb128        0x3                     /* DW_AT_name */
> -	.uleb128	0x8			/* DW_FORM_string */
> -        .uleb128        0x49                    /* DW_AT_type */
> -        .uleb128        0x13                    /* DW_FORM_ref4 */
> -        .uleb128        0x1c                    /* DW_AT_const_value */
> -        .uleb128        0xb                     /* DW_FORM_data1 */
> -	.byte		0x0			/* Terminator */
> -	.byte		0x0			/* Terminator */
> -
> -        .uleb128        0x9                     /* abbrev code */
> -        .uleb128        0x26                    /* TAG: DW_TAG_const_type */
> -        .byte           0x0                     /* DW_children_no */
> -        .uleb128        0x49                    /* DW_AT_type */
> -        .uleb128        0x13                    /* DW_FORM_ref4 */
> -	.byte		0x0			/* Terminator */
> -	.byte		0x0			/* Terminator */
> -
> -	.uleb128	0xa			/* abbrev code */
> -	.uleb128	0x34			/* TAG: DW_TAG_variable */
> -	.byte		0x0			/* DW_children_no */
> -	.uleb128	0x3			/* DW_AT_name */
> -	.uleb128	0x8			/* DW_FORM_string */
> -	.uleb128	0x49			/* DW_AT_type */
> -	.uleb128	0x13			/* DW_FORM_ref4 */
> -	.uleb128	0x02			/* DW_AT_location */
> -	.uleb128	0xa			/* DW_FORM_block1 */
> -	.byte		0x0			/* Terminator */
> -	.byte		0x0			/* Terminator */
> -
> -	.byte		0x0			/* Terminator */
> -	.byte		0x0			/* Terminator */
> -
> -/* Line table */
> -	.section .debug_line
> -.Lline1_begin:
> -	.4byte		.Lline1_end - .Lline1_start	/* Initial length */
> -.Lline1_start:
> -	.2byte		2			/* Version */
> -	.4byte		.Lline1_lines - .Lline1_hdr	/* header_length */
> -.Lline1_hdr:
> -	.byte		1			/* Minimum insn length */
> -	.byte		1			/* default_is_stmt */
> -	.byte		1			/* line_base */
> -	.byte		1			/* line_range */
> -	.byte		0x10			/* opcode_base */
> -
> -	/* Standard lengths */
> -	.byte		0
> -	.byte		1
> -	.byte		1
> -	.byte		1
> -	.byte		1
> -	.byte		0
> -	.byte		0
> -	.byte		0
> -	.byte		1
> -	.byte		0
> -	.byte		0
> -	.byte		1
> -	.byte		0
> -	.byte		0
> -	.byte		0
> -
> -	/* Include directories */
> -	.byte		0
> -
> -	/* File names */
> -	.ascii		"file1.txt\0"
> -	.uleb128	0
> -	.uleb128	0
> -	.uleb128	0
> -
> -	.byte		0
> -
> -.Lline1_lines:
> -	.byte		0	/* DW_LNE_set_address */
> -	.uleb128	5
> -	.byte		2
> -	.4byte		.Lbegin_func_cu1
> -
> -	.byte		3	/* DW_LNS_advance_line */
> -	.sleb128	3	/* ... to 4 */
> -
> -	.byte		1	/* DW_LNS_copy */
> -
> -	.byte		1	/* DW_LNS_copy (second time as an end-of-prologue marker) */
> -
> -	.byte		0	/* DW_LNE_set_address */
> -	.uleb128	5
> -	.byte		2
> -	.4byte		.Lend_func_cu1
> -
> -	.byte		0	/* DW_LNE_end_of_sequence */
> -	.uleb128	1
> -	.byte		1
> -
> -.Lline1_end:
> -#ifdef __arm__
> -	.section	.note.GNU-stack,"",%progbits
> -#else
> -	.section	.note.GNU-stack,"",@progbits
> -#endif
> diff --git a/gdb/testsuite/gdb.dwarf2/dw2-const.exp b/gdb/testsuite/gdb.dwarf2/dw2-const.exp
> index 93ddfaa0f2f..1492b09c93b 100644
> --- a/gdb/testsuite/gdb.dwarf2/dw2-const.exp
> +++ b/gdb/testsuite/gdb.dwarf2/dw2-const.exp
> @@ -17,10 +17,56 @@ load_lib dwarf.exp
>   # This test can only be run on targets which support DWARF-2 and use gas.
>   require dwarf2_support
>   
> -standard_testfile .S
> +standard_testfile main.c -debug.S
>   
> -if {[prepare_for_testing_full "failed to prepare" \
> -	 [list $testfile debug main.c debug $srcfile nodebug]]} {
> +# Set up the DWARF for the test.
> +
> +set asm_file [standard_output_file $srcfile2]
> +Dwarf::assemble $asm_file {
> +    global srcdir subdir srcfile
> +    declare_labels int int8 const_type const_type_2
> +
> +    cu {version 2} {
> +	DW_TAG_compile_unit {
> +	    DW_AT_name file1.txt DW_FORM_string
> +	    DW_AT_producer {GNU C 3.3.3} DW_FORM_string
> +	    DW_AT_language @DW_LANG_C89
> +	} {
> +	    DW_TAG_constant {
> +		DW_AT_name twelve DW_FORM_string
> +		DW_AT_type :$const_type_2
> +		DW_AT_const_value 12 DW_FORM_data1
> +	    }
> +	    const_type_2: DW_TAG_const_type {
> +		DW_AT_type :$int
> +	    }
> +	    DW_TAG_variable {
> +		DW_AT_name val8 DW_FORM_string
> +		DW_AT_type :$const_type
> +		DW_AT_location {
> +		    DW_OP_consts -4294967296
> +		    DW_OP_stack_value
> +		} SPECIAL_expr
> +	    }
> +	    const_type: DW_TAG_const_type {
> +		DW_AT_type :$int8
> +	    }
> +	    int: DW_TAG_base_type {
> +		DW_AT_name int DW_FORM_string
> +		DW_AT_byte_size 4 DW_FORM_data1
> +		DW_AT_encoding @DW_ATE_signed
> +	    }
> +	    int8: DW_TAG_base_type {
> +		DW_AT_name int8 DW_FORM_string
> +		DW_AT_byte_size 8 DW_FORM_data1
> +		DW_AT_encoding @DW_ATE_signed
> +	    }
> +	}
> +    }
> +}
> +
> +if {[prepare_for_testing "failed to prepare" ${testfile} \
> +	 [list $srcfile $asm_file] nodebug]} {
>       return
>   }
>   
> 
> base-commit: 1678d7d3d2e4cf83cda5a96334a0326573ad0f7c
  

>>>>> "Tom" == Tom de Vries <tdevries@suse.de> writes:

Tom> Then I ran it with target board unix/-m32, and ran into:
Tom> ...
Tom> (gdb) print/x val8^M
Tom> $2 = 0x0^M
Tom> (gdb) FAIL: gdb.dwarf2/dw2-const.exp: print/x val8
Tom> ...

Yeah, me too.

I wonder if there's some gas oddity here.  The DWARF doesn't seem to be
notably weird or word-size-dependent.  I see in the old .S:

>> -#if 0 /* gas encodes it explicitly.  */
>> -        .slab128        0xffffffff00000000
>> -#endif
>> -#if 0 /* gas encoded it correctly - formed GDB FAILed.  */
>> -        .sleb128        -4294967296
>> -#endif
>> -#if 1 /* Rather encode sleb128 by hand.  */
>> -        .byte           0x80, 0x80, 0x80, 0x80, 0x70
>> -#endif

So hmm.

But maybe this is some kind of extension we would want to support in the
DWARF assembler.

Anyway still looking into this.

Tom
  

On 5/29/26 4:58 PM, Tom Tromey wrote:
>>>>>> "Tom" == Tom de Vries <tdevries@suse.de> writes:
> 
> Tom> Then I ran it with target board unix/-m32, and ran into:
> Tom> ...
> Tom> (gdb) print/x val8^M
> Tom> $2 = 0x0^M
> Tom> (gdb) FAIL: gdb.dwarf2/dw2-const.exp: print/x val8
> Tom> ...
> 
> Yeah, me too.
> 
> I wonder if there's some gas oddity here.  The DWARF doesn't seem to be
> notably weird or word-size-dependent.  I see in the old .S:
> 
>>> -#if 0 /* gas encodes it explicitly.  */
>>> -        .slab128        0xffffffff00000000
>>> -#endif
>>> -#if 0 /* gas encoded it correctly - formed GDB FAILed.  */
>>> -        .sleb128        -4294967296
>>> -#endif
>>> -#if 1 /* Rather encode sleb128 by hand.  */
>>> -        .byte           0x80, 0x80, 0x80, 0x80, 0x70
>>> -#endif
> 
> So hmm.
> 
> But maybe this is some kind of extension we would want to support in the
> DWARF assembler.
> 
> Anyway still looking into this.

I found the reason for the discrepancy.

Before the patch, with unix/m32, the adress size is 8:
...
   Compilation Unit @ offset 0x2df:
    Length:        0x6f (32-bit)
    Version:       2
    Abbrev Offset: 0x1bb
    Pointer Size:  8
  <0><2ea>: Abbrev Number: 1 (DW_TAG_compile_unit)
     <2eb>   DW_AT_stmt_list   : 0x200
     <2ef>   DW_AT_name        : file1.txt
     <2f9>   DW_AT_producer    : GNU C 3.3.3
     <305>   DW_AT_language    : 1       (ANSI C)
...

After the patch, it's 4.

In dwarf_expr_context::execute_stack_op, we do:
...
	case DW_OP_consts:
           op_ptr = safe_read_sleb128 (op_ptr, op_end, &offset);
           result = offset;
           result_val = value_from_ulongest (address_type, result);
           break;
...
and if address_type has size 4, result_val is 0.

Thanks,
- Tom
  

>>>>> "Tom" == Tom de Vries <tdevries@suse.de> writes:

Tom> I found the reason for the discrepancy.

Tom> Before the patch, with unix/m32, the adress size is 8:

Thank you.  I sent a v2 with this change.

Tom