[PATCH 2/2] gdb/dwarf: skip broken .debug_macro.dwo

[Simon Marchi <simon.marchi@efficios.com>]

Running gdb.base/errno.exp with gcc <= 13 with split DWARF results in:

    $ make check TESTS="gdb.base/errno.exp" RUNTESTFLAGS="CC_FOR_TARGET=gcc-13 --target_board=fission"
    (gdb) break -qualified main
    /home/smarchi/src/binutils-gdb/gdb/dwarf2/read.c:7549: internal-error: locate_dwo_sections: Assertion `!dw_sect->readin' failed.
    A problem internal to GDB has been detected,
    further debugging may prove unreliable.
    ...
    FAIL: gdb.base/errno.exp: macros: gdb_breakpoint: set breakpoint at main (GDB internal error)

The assert being hit has been added in 28f15782adab ("gdb/dwarf: read
multiple .debug_info.dwo sections"), but it merely exposed an existing
problem.

gcc versions <= 13 are affected by this bug:

  https://gcc.gnu.org/bugzilla/show_bug.cgi?id=111409

Basically, it produces .dwo files with multiple .debug_macro.dwo
sections, with some unresolved links between them.  I think that this
macro debug info is unusable, and all we can do is ignore it.

In locate_dwo_sections, if we detect a second .debug_macro.dwo section,
forget about the previous .debug_macro.dwo and any subsequent one.  This
will effectively make it as if the macro debug info wasn't there at all.

The errno test seems happy with it:

    # of expected passes            84
    # of expected failures          8

Change-Id: I6489b4713954669bf69f6e91865063ddcd1ac2c8
---
 gdb/dwarf2/read.c | 20 +++++++++++++++++++-
 1 file changed, 19 insertions(+), 1 deletion(-)

diff --git a/gdb/dwarf2/read.c b/gdb/dwarf2/read.c
index 550968abc95c..63c0c007563e 100644
--- a/gdb/dwarf2/read.c
+++ b/gdb/dwarf2/read.c
@@ -7516,6 +7516,7 @@ cutu_reader::locate_dwo_sections (objfile *objfile, dwo_file &dwo_file)
 {
   const struct dwop_section_names *names = &dwop_section_names;
   dwo_sections &dwo_sections = dwo_file.sections;
+  bool complained_about_macro_already = false;
 
   for (asection *sec : gdb_bfd_sections (dwo_file.dbfd))
     {
@@ -7534,7 +7535,24 @@ cutu_reader::locate_dwo_sections (objfile *objfile, dwo_file &dwo_file)
       else if (names->macinfo_dwo.matches (sec->name))
 	dw_sect = &dwo_sections.macinfo;
       else if (names->macro_dwo.matches (sec->name))
-	dw_sect = &dwo_sections.macro;
+	{
+	  /* gcc versions <= 13 generate multiple .debug_macro.dwo sections with
+	     some unresolved links between them.  It's not usable, so do as if
+	     there were not there.  */
+	  if (!complained_about_macro_already)
+	    {
+	      if (dwo_sections.macro.s.section == nullptr)
+		dw_sect = &dwo_sections.macro;
+	      else
+		{
+		  complaint (_("Multiple .debug_macro.dwo sections found in "
+			       "%s, ignoring them."), dwo_file.dbfd->filename);
+
+		  dwo_sections.macro = dwarf2_section_info {};
+		  complained_about_macro_already = true;
+		}
+	    }
+	}
       else if (names->rnglists_dwo.matches (sec->name))
 	dw_sect = &dwo_sections.rnglists;
       else if (names->str_dwo.matches (sec->name))
-- 
2.49.0