Hi gcc hackers, binutils hackers,
Nick, Jakub and I were discussing the gcc patch below and all the ways
it is wrong. Most things can be fixed in the spec. Like only passing
-gdwarf if we are generating DWARF and passing the right DWARF version
as -gdwarf-N for the version that gcc itself creates. But whether or
not we want gas to generate .debug_line info is a bit tricky. But when
giving -gdwarf-N gas will always try to generate a .debug_line section
and error out when there is already one.
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))
On Mon, Aug 24, 2020 at 02:56:58PM +0200, Mark Wielaard wrote:
> 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(+)
>
> 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
> --
> 2.18.4
>
