[Bug default/24468] dwz -m generates partial unit without import

["vries at gcc dot gnu.org" <sourceware-bugzilla@sourceware.org>]

https://sourceware.org/bugzilla/show_bug.cgi?id=24468

--- Comment #1 from Tom de Vries <vries at gcc dot gnu.org> ---
So, what happens is this: the partial unit at 2b5 in the multifile contains as
first die:
...
 <1><2be>: Abbrev Number: 5 (DW_TAG_const_type)
    <2bf>   DW_AT_type        : <0x4c>
...
which refers to:
...
 <1><4c>: Abbrev Number: 18 (DW_TAG_typedef)
    <4d>   DW_AT_name        : (indirect string, offset: 0x54c): size_t
    <51>   DW_AT_decl_file   : 1
    <52>   DW_AT_decl_line   : 216
    <53>   DW_AT_type        : <0x344>
...
in another partial unit in the multifile.

When matching dies in the input file against the dies in the multifile during
finalize_multifile, we compare 2be to 394:
...
 <1><389>: Abbrev Number: 24 (DW_TAG_typedef)
    <38a>   DW_AT_name        : (indirect string, offset: 0x226): size_t
    <38e>   DW_AT_decl_file   : 2
    <38f>   DW_AT_decl_line   : 216
    <390>   DW_AT_type        : <0x14>
 <1><394>: Abbrev Number: 7 (DW_TAG_const_type)
    <395>   DW_AT_type        : <0x389>
...
which then fails because of a mismatch in DW_FORM (DW_FORM_ref_addr vs
DW_FORM_ref_udata).

OTOH, the long double die in the input file matches the one in the multifile.

Subsequently, we hit this in create_import_tree, and skip generating an import
for the partial unit due to 2be not having a duplicate:
...
      if (unlikely (fi_multifile) && rdie->die_nextdup == NULL)
        {
          pu->u1.cu_icu = NULL;
          continue;
        }
...
OTOH, we need an import for the partial unit due to the long double, which does
have a duplicate.

Tentative patch:
...
@@ -5779,10 +5798,15 @@ create_import_tree (void)
       for (rdie = pu->cu_die->die_child;
           rdie->die_named_namespace; rdie = rdie->die_child)
        ;
-      if (unlikely (fi_multifile) && rdie->die_nextdup == NULL)
+      if (unlikely (fi_multifile))
        {
-         pu->u1.cu_icu = NULL;
-         continue;
+         while (rdie->die_nextdup == NULL && rdie->die_sib)
+           rdie = rdie->die_sib;
+         if (rdie->die_nextdup == NULL)
+           {
+             pu->u1.cu_icu = NULL;
+             continue;
+           }
        }
       npus++;
       if (pu->cu_version > new_pu_version)
...

Using the tentative patch, we get the missing import in CU elf-init.c:
...
 <1><2e4>: Abbrev Number: 15 (DW_TAG_imported_unit)
    <2e5>   DW_AT_import      : <alt 0x2b5>
...
and find again the missing long double with gdb:
...
$ gdb 1 -ex "info types" -batch | egrep "long double|^File"
File /usr/include/bits/types.h:
File /usr/include/libio.h:
File /usr/lib64/gcc/x86_64-suse-linux/7/include/stddef.h:
File <unknown>:
        typedef long double;
...

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