[5/5] Add --gdwarf-5 to ASM_SPEC

Message ID 20200824125658.22526-6-mark@klomp.org
State New
Headers show
Series
  • [1/5] Don't enable -gvariable-location-views by default for DWARF5.
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Commit Message

Mark Wielaard Aug. 24, 2020, 12:56 p.m.
This is needed to get DWARF version 5 .debug_line tables.
It is also obviously wrong. It needs a check for whether as supports
--gdwarf-<version> for all versions we support and it should only
be added when generating DWARF debug information for the specific
DWARF version we are generating.

It also needs some fixes to binutils, to make sure the line table is
generated correctly:
https://sourceware.org/pipermail/binutils/2020-August/112685.html
And to make sure it can read the generated line table itself:
https://sourceware.org/pipermail/binutils/2020-August/112966.html
---
 gcc/gcc.c | 5 +++++
 1 file changed, 5 insertions(+)

-- 
2.18.4

Comments

Jason Merrill via Gcc-patches Aug. 29, 2020, 2:34 p.m. | #1
On Sat, Aug 29, 2020 at 5:24 AM Mark Wielaard <mark@klomp.org> wrote:
>

> Hi,

>

> On Wed, Aug 26, 2020 at 04:38:21PM -0700, H.J. Lu wrote:

> > On Wed, Aug 26, 2020 at 2:38 PM Mark Wielaard <mark@klomp.org> wrote:

> > > Would it be possible to have something like the following in gas, so

> > > that it doesn't try generating a .debug_line section if there already

> > > is one, even when -gdwarf-N is given (unless the assembly also

> > > contains .loc directives because that shows the user is really

> > > confused)?

> > >

> > > diff --git a/gas/dwarf2dbg.c b/gas/dwarf2dbg.c

> > > index e4ba56d82ba..c0c09f4e9d0 100644

> > > --- a/gas/dwarf2dbg.c

> > > +++ b/gas/dwarf2dbg.c

> > > @@ -2626,7 +2626,7 @@ dwarf2_init (void)

> > >

> > >

> > >  /* Finish the dwarf2 debug sections.  We emit .debug.line if there

> > > -   were any .file/.loc directives, or --gdwarf2 was given, or if the

> > > +   were any .file/.loc directives, or --gdwarf2 was given, and if the

> > >     file has a non-empty .debug_info section and an empty .debug_line

> > >     section.  If we emit .debug_line, and the .debug_info section is

> > >     empty, we also emit .debug_info, .debug_aranges and .debug_abbrev.

> > > @@ -2650,9 +2650,16 @@ dwarf2_finish (void)

> > >    empty_debug_line = line_seg == NULL || !seg_not_empty_p (line_seg);

> > >

> > >    /* We can't construct a new debug_line section if we already have one.

> > > -     Give an error.  */

> > > +     Give an error if we have seen any .loc, otherwise trust the user

> > > +     knows what they are doing and want to generate the .debug_line

> > > +     (and all other debug sections) themselves.  */

> > >    if (all_segs && !empty_debug_line)

> > > -    as_fatal ("duplicate .debug_line sections");

> > > +    {

> > > +      if (dwarf2_loc_directive_seen)

> > > +       as_fatal ("duplicate .debug_line sections");

> > > +      else

> > > +       return;

> > > +    }

> > >

> > >    if ((!all_segs && emit_other_sections)

> > >        || (!emit_other_sections && !empty_debug_line))

> > >

> >

> > I have run into this issue before.  "as -g" shouldn't silently

> > generate incorrect debug info when input assembly codes already

> > contain debug directives.  AS should either issue an error or

> > ignore -g.

>

> Right, that is what this patch does for .debug_line.  gas already

> doesn't generate .debug_info, .debug_aranges and .debug_abbrev if

> .debug_info is non-empty, even if -g is given.

>

> > In either case, we need a testcase  to verify it.

>

> Right, and the documentation needs to be update.  But first we have to

> know whether the gas maintainers think this is the right approach.

>


-g should be ignored in this case.


-- 
H.J.

Patch

diff --git a/gcc/gcc.c b/gcc/gcc.c
index 10bc9881aed3..98b10e7cd154 100644
--- a/gcc/gcc.c
+++ b/gcc/gcc.c
@@ -1882,6 +1882,11 @@  init_spec (void)
   }
 #endif
 
+  static const char dv[] = "--gdwarf-5 ";
+  obstack_grow (&obstack, dv, sizeof (dv) - 1);
+  obstack_grow0 (&obstack, asm_spec, strlen (asm_spec));
+  asm_spec = XOBFINISH (&obstack, const char *);
+
 #if defined LINK_EH_SPEC || defined LINK_BUILDID_SPEC || \
     defined LINKER_HASH_STYLE
 # ifdef LINK_BUILDID_SPEC