[Bug gdb/29558] New: [gdb/symtab] Handle gas-generated debug info (DW_TAG_unspecified_type)

[Bug gdb/29558] New: [gdb/symtab] Handle gas-generated debug info (DW_TAG_unspecified_type)

[vries at gcc dot gnu.org]

https://sourceware.org/bugzilla/show_bug.cgi?id=29558

            Bug ID: 29558
           Summary: [gdb/symtab] Handle gas-generated debug info
                    (DW_TAG_unspecified_type)
           Product: gdb
           Version: HEAD
            Status: NEW
          Severity: normal
          Priority: P2
         Component: gdb
          Assignee: unassigned at sourceware dot org
          Reporter: vries at gcc dot gnu.org
  Target Milestone: ---

I.

A recent commit 5578fbf672e ("GAS: Add a return type tag to DWARF DIEs
generated for function symbols") fixes a problem with gas-generated dwarf info.

So, let's see if we can reproduce the problem and test the fix in gdb.

Multi-source test-case:
...
$ cat test.c
extern int foo (void);

int
main (void)
{
  int res = foo ();
  return res;
}
$ cat test2.c
int
foo (void)
{
  return 0;
}
...

Test script:
...
$ cat compile.sh
#!/bin/sh

as=/home/vries/binutils/install/bin/as

gcc -c -g test.c
gcc -S test2.c
$as --64 -gdwarf-5 -o test2.o test2.s
gcc test.o test2.o 

./gdb.sh -batch a.out -ex start -ex "p foo" -ex "p (int) foo ()"
...


II. 2.38

Using $as from 2.38:
...
$ ./compile.sh
Temporary breakpoint 1 at 0x40049f: file test.c, line 6.

Temporary breakpoint 1, main () at test.c:6
6         int res = foo ();
$1 = {<text variable, no debug info>} 0x4004ac <foo>
$2 = 0
...
Looks as expected.

III. 2.39

Using $as from 2.39:
...
$ ./compile.sh
Temporary breakpoint 1 at 0x40049f: file test.c, line 6.

Temporary breakpoint 1, main () at test.c:6
6         int res = foo ();
$1 = {void (void)} 0x4004ac <foo>
Invalid cast.
...
So, this is the bug the commit is trying to fix.


III. current trunk

Using $as from current trunk:
...
$ ./compile.sh
Dwarf Error: unexpected tag 'DW_TAG_unspecified_type' at offset 0xf4
Temporary breakpoint 1 at 0x40049f: file test.c, line 6.

Temporary breakpoint 1, main () at test.c:6
6         int res = foo ();
Dwarf Error: unexpected tag 'DW_TAG_unspecified_type' at offset 0xf4
Dwarf Error: unexpected tag 'DW_TAG_unspecified_type' at offset 0xf4
...

So, either the debug info is invalid, or gdb needs to learn how to handle this.

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[Bug gdb/29558] [gdb/symtab] Handle gas-generated debug info (DW_TAG_unspecified_type)

[vries at gcc dot gnu.org]

https://sourceware.org/bugzilla/show_bug.cgi?id=29558

--- Comment #1 from Tom de Vries <vries at gcc dot gnu.org> ---
See also PR17271 - "unsupported tag: DW_TAG_unspecified_type"

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[Bug gdb/29558] [gdb/symtab] Handle gas-generated debug info (DW_TAG_unspecified_type)

[vries at gcc dot gnu.org]

https://sourceware.org/bugzilla/show_bug.cgi?id=29558

Tom de Vries <vries at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
                 CC|                            |nickc at redhat dot com

--- Comment #2 from Tom de Vries <vries at gcc dot gnu.org> ---
Debug info looks like:
...
  Compilation Unit @ offset 0xf4:
   Length:        0x35 (32-bit)
   Version:       5
   Unit Type:     DW_UT_compile (1)
   Abbrev Offset: 0xa3
   Pointer Size:  8
 <0><100>: Abbrev Number: 3 (DW_TAG_unspecified_type)
 <0><101>: Abbrev Number: 1 (DW_TAG_compile_unit)
    <102>   DW_AT_stmt_list   : 0x123
    <106>   DW_AT_low_pc      : 0x4004ac
    <10e>   DW_AT_high_pc     : 11
    <10f>   DW_AT_name        : test2.s
    <113>   DW_AT_comp_dir    : /home/vries/gdb_versions/devel
    <117>   DW_AT_producer    : GNU AS 2.39.50
    <11b>   DW_AT_language    : 32769   (MIPS assembler)
 <1><11d>: Abbrev Number: 2 (DW_TAG_subprogram)
    <11e>   DW_AT_name        : (indirect string, offset: 0x241): foo
    <122>   DW_AT_external    : 1
    <122>   DW_AT_type        : <0x100>
    <123>   DW_AT_low_pc      : 0x4004ac
    <12b>   DW_AT_high_pc     : 11
...

OK, that looks highly unregular, the DW_TAG_unspecified_type die as a top-level
DIE.

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[Bug gdb/29558] [gdb/symtab] Handle gas-generated debug info (DW_TAG_unspecified_type)

[vries at gcc dot gnu.org]

https://sourceware.org/bugzilla/show_bug.cgi?id=29558

--- Comment #3 from Tom de Vries <vries at gcc dot gnu.org> ---
In the dwarf-5 standard I read:
...
For each compilation unit compiled with a DWARF producer, a contribution is
made to the .debug_info section of the object file. Each such contribution
consists of a compilation unit header followed by a single DW_TAG_compile_unit
or DW_TAG_partial_unit debugging information entry, together with its children.
...

Ok, so this is in fact incorrect dwarf.

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[Bug gdb/29558] [gdb/symtab] Handle gas-generated debug info (DW_TAG_unspecified_type)

[vries at gcc dot gnu.org]

https://sourceware.org/bugzilla/show_bug.cgi?id=29558

--- Comment #4 from Tom de Vries <vries at gcc dot gnu.org> ---
(In reply to Tom de Vries from comment #3)
> Ok, so this is in fact incorrect dwarf.

Filed gas PR29559 - "gas generated incorrect debug info (top-level
DW_TAG_unspecified_type DIE)".

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[Bug gdb/29558] [gdb/symtab] Handle gas-generated debug info (DW_TAG_unspecified_type)

[vries at gcc dot gnu.org]

https://sourceware.org/bugzilla/show_bug.cgi?id=29558

--- Comment #5 from Tom de Vries <vries at gcc dot gnu.org> ---
Created attachment 14326
  --> https://sourceware.org/bugzilla/attachment.cgi?id=14326&action=edit
Dwarf assembly test-case

Currently, this fails:
...
(gdb) PASS: gdb.dwarf2/dw2-unspecified-type.exp: p ((int (*) ()) foo) ()
p (int) foo ()^M
Invalid cast.^M
(gdb) FAIL: gdb.dwarf2/dw2-unspecified-type.exp: p (int) foo ()
...
because DW_TAG_unspecified_type is translated as void.

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[Bug gdb/29558] [gdb/symtab] Handle gas-generated debug info (DW_TAG_unspecified_type)

[vries at gcc dot gnu.org]

https://sourceware.org/bugzilla/show_bug.cgi?id=29558

Tom de Vries <vries at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
                 CC|                            |kevinb at redhat dot com

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[Bug gdb/29558] [gdb/symtab] Handle gas-generated debug info (DW_TAG_unspecified_type)

[vries at gcc dot gnu.org]

https://sourceware.org/bugzilla/show_bug.cgi?id=29558

--- Comment #6 from Tom de Vries <vries at gcc dot gnu.org> ---
(In reply to Tom de Vries from comment #1)
> See also PR17271 - "unsupported tag: DW_TAG_unspecified_type"

I've looked now at that one, and it looks unrelated, that's the case when a
DW_TAG_unspecificed_type DIE has a name attribute.

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[Bug symtab/29558] [gdb/symtab] Handle gas-generated debug info (DW_TAG_unspecified_type)

[vries at gcc dot gnu.org]

https://sourceware.org/bugzilla/show_bug.cgi?id=29558

Tom de Vries <vries at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
          Component|gdb                         |symtab

--- Comment #7 from Tom de Vries <vries at gcc dot gnu.org> ---
https://sourceware.org/pipermail/gdb-patches/2022-September/191753.html

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[Bug symtab/29558] [gdb/symtab] Handle gas-generated debug info (DW_TAG_unspecified_type)

[vries at gcc dot gnu.org]

https://sourceware.org/bugzilla/show_bug.cgi?id=29558

Tom de Vries <vries at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
         Resolution|---                         |FIXED
             Status|NEW                         |RESOLVED
   Target Milestone|---                         |13.1

--- Comment #8 from Tom de Vries <vries at gcc dot gnu.org> ---
https://sourceware.org/git/?p=binutils-gdb.git;a=commit;h=a34a90995ae7c2f0c0b79ad32d8087d507fe42db

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[Bug symtab/29558] [gdb/symtab] Handle gas-generated debug info (DW_TAG_unspecified_type)

[mark at klomp dot org]

https://sourceware.org/bugzilla/show_bug.cgi?id=29558

Mark Wielaard <mark at klomp dot org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
                 CC|                            |mark at klomp dot org

--- Comment #9 from Mark Wielaard <mark at klomp dot org> ---
Created attachment 14632
  --> https://sourceware.org/bugzilla/attachment.cgi?id=14632&action=edit
tests: Handle DW_TAG_unspecified_type in funcretval test

This patch just fixes the testcase to check for DW_TAG_unspecified_type as
return type.
With your test binary tests/funcretval now prints:

() _start: returns unspecified type
() main: return value location: {0x50, 0}

But maybe a better fix is for dwfl_module_return_value_location to return zero
(which technically means that the function doesn't have a return value).

Opinions?

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[Bug symtab/29558] [gdb/symtab] Handle gas-generated debug info (DW_TAG_unspecified_type)

[mark at klomp dot org]

https://sourceware.org/bugzilla/show_bug.cgi?id=29558

--- Comment #10 from Mark Wielaard <mark at klomp dot org> ---
(In reply to Mark Wielaard from comment #9)
> Created attachment 14632 [details]
> tests: Handle DW_TAG_unspecified_type in funcretval test
> 
> This patch just fixes the testcase to check for DW_TAG_unspecified_type as
> return type.
> With your test binary tests/funcretval now prints:
> 
> () _start: returns unspecified type
> () main: return value location: {0x50, 0}
> 
> But maybe a better fix is for dwfl_module_return_value_location to return
> zero (which technically means that the function doesn't have a return value).
> 
> Opinions?

Sorry, this patch was for elfutils, specifically
https://sourceware.org/bugzilla/show_bug.cgi?id=30047 I was just looking how
gdb handled this.

Apologies.

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