PR23425, unresolved symbol diagnostic
Commit Message
dwarf2.c code reasonably assumes that debug info is local to a file,
an assumption now violated by gcc, resulting in "DWARF error: invalid
abstract instance DIE ref" or wrong details when attempting to print
linker error messages with file, function and line reported.
This is because find_abstract_instance is only prepared to handle
DW_FORM_ref_addr when the .debug_info section referenced is in the
current file. When that isn't the case, relocations to access another
file's .debug_info will typically be against a symbol defined at the
start of that .debug_info section, plus an addend. Since the dwarf2.c
code only considers the current file's debug info, that symbol will be
undefined, resolving to zero. In effect the ref_addr will wrongly
resolve to the current file's .debug_info.
This patch avoids the problem by treating relocations in debug
sections against undefined symbols in a similar manner to the way
relocations against symbols defined in discarded sections are
resolved. They result in a zero value (except in .debug_ranges)
regardless of the addend.
I think this should be OK for all the gdb uses of
bfd_simple_get_relocated_section_contents or similar code in
compile-object-load.c, but I won't commit this immediately to give gdb
folk time to comment.
PR 23425
* reloc.c (bfd_generic_get_relocated_section_contents): Zero reloc
fields in debug sections when reloc is against an undefined symbol
and called from bfd_simple_get_relocated_section_contents or
similar.
* dwarf2.c (find_abstract_instance): Return true for zero offset
DW_FORM_ref_addr without returning values.
Comments
>>>>> "Alan" == Alan Modra <amodra@gmail.com> writes:
Alan> I think this should be OK for all the gdb uses of
Alan> bfd_simple_get_relocated_section_contents or similar code in
Alan> compile-object-load.c, but I won't commit this immediately to give gdb
Alan> folk time to comment.
There should be gdb test cases covering the relocation cases.
For the compile feature you'll need to make sure your gcc is
compile-capable and that the needed library and plugin are installed.
However, I believe relocation isn't only used for the compile feature.
There's this in dwarf2read.c:
/* When debugging .o files, we may need to apply relocations; see
http://sourceware.org/ml/gdb-patches/2002-04/msg00136.html .
We never compress sections in .o files, so we only need to
try this when the section is not compressed. */
retbuf = symfile_relocate_debug_section (objfile, sectp, buf);
I don't know if there is a test case for this or not -- I'd hope so.
Tom
On 09/11/2018 05:04 PM, Tom Tromey wrote:
>>>>>> "Alan" == Alan Modra <amodra@gmail.com> writes:
>
> Alan> I think this should be OK for all the gdb uses of
> Alan> bfd_simple_get_relocated_section_contents or similar code in
> Alan> compile-object-load.c, but I won't commit this immediately to give gdb
> Alan> folk time to comment.
>
> There should be gdb test cases covering the relocation cases.
Yeah, you can debug an unrelocated .o file directly,
like "file foo.o". The canonical testcase for that, I think is
gdb.base/relocate.exp.
>
> For the compile feature you'll need to make sure your gcc is
> compile-capable and that the needed library and plugin are installed.
>
> However, I believe relocation isn't only used for the compile feature.
> There's this in dwarf2read.c:
>
> /* When debugging .o files, we may need to apply relocations; see
> http://sourceware.org/ml/gdb-patches/2002-04/msg00136.html .
> We never compress sections in .o files, so we only need to
> try this when the section is not compressed. */
> retbuf = symfile_relocate_debug_section (objfile, sectp, buf);
>
> I don't know if there is a test case for this or not -- I'd hope so.
gdb.base/relocate.exp likely covers this.
Thanks,
Pedro Alves
@@ -2837,7 +2837,9 @@ find_abstract_instance (struct comp_unit * unit,
info_ptr = unit->stash->info_ptr_memory;
info_ptr_end = unit->stash->info_ptr_end;
total = info_ptr_end - info_ptr;
- if (!die_ref || die_ref >= total)
+ if (!die_ref)
+ return TRUE;
+ else if (die_ref >= total)
{
_bfd_error_handler
(_("DWARF error: invalid abstract instance DIE ref"));
@@ -8259,7 +8259,18 @@ bfd_generic_get_relocated_section_contents (bfd *abfd,
goto error_return;
}
- if (symbol->section && discarded_section (symbol->section))
+ /* Zap reloc field when the symbol is from a discarded
+ section, ignoring any addend. Do the same when called
+ from bfd_simple_get_relocated_section_contents for
+ undefined symbols in debug sections. This is to keep
+ debug info reasonably sane, in particular so that
+ DW_FORM_ref_addr to another file's .debug_info isn't
+ confused with an offset into the current file's
+ .debug_info. */
+ if ((symbol->section != NULL && discarded_section (symbol->section))
+ || (symbol->section == bfd_und_section_ptr
+ && (input_section->flags & SEC_DEBUGGING) != 0
+ && link_info->input_bfds == link_info->output_bfd))
{
bfd_byte *p;
static reloc_howto_type none_howto