[PATCH] DWARFv5: Handle DW_MACRO_define_strx and DW_MACRO_undef_strx macro entries.

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[PATCH] DWARFv5: Handle DW_MACRO_define_strx and DW_MACRO_undef_strx macro entries.

Achra, Nitika
Hi Simon,

I have made some changes to handle these entries when using .dwo file. Also,
tested this patch with the clang 11 stable build. Clang 11 is not
emitting DW_MACRO_define_strx and DW_MACRO_undef_strx with
-gsplit-dwarf. However, clang 12 is emitting them with -gsplit-dwarf.
Tested with -gsplit-dwarf using clang 12.

Regards,
Nitika

---
GDB is not able to print the macro values with -gdwarf-5 for clang
generated binaries. Clang is emitting DW_MACRO_define_strx and
DW_MACRO_undef_strx entries in .debug_macro section which are not
supported in GDB. This patch handles them.

DW_MACRO_define_strx and DW_MACRO_undef_strx are added in DWARFv5.
They have two operands. The first operand encodes the line number of
the #define or #undef macro directive. The second operand identifies
a string; it is represented using an unsigned LEB128 encoded value,
which is interpreted as a zero-based index into an array of offsets
in the .debug_str_offsets section. This is as per the section 6.3.2.1
of Dwarf Debugging Information Format Version 5.

Test case used:
 #define MAX_SIZE 10
int main(void)
{
   int size = 0;
   size = size + MAX_SIZE;

   printf("\n The value of size is [%d]\n",size);

   return 0;
}

clang -gdwarf-5 -fdebug-macro  macro.c -o macro.out

Before the patch:

gdb -q  macro.out -ex "start" -ex "p MAX_SIZE"
Reading symbols from macro.out...
Temporary breakpoint 1 at 0x4004df: file macro.c, line 7.
Starting program: /home/nitika/workspace/macro.out

Temporary breakpoint 1, main () at macro.c:7
7          int size = 0;
No symbol "MAX_SIZE" in current context.

After the patch:

gdb -q  macro.out -ex "start" -ex "p MAX_SIZE"
Reading symbols from macro.out...
Temporary breakpoint 1 at 0x4004df: file macro.c, line 7.
Starting program: /home/nitika/workspace/macro.out

Temporary breakpoint 1, main () at macro.c:7
7          int size = 0;
$1 = 10

Tested by running the testsuite before and after the patch with
 -gdwarf-5 and there is no increase in the number of test cases
that fails. Used clang 11.0.0.

gdb/ChangeLog:

        * dwarf2/macro.c (dwarf_decode_macro_bytes): Handle DW_MACRO_define_strx
        and DW_MACRO_undef_strx.
        (dwarf_decode_macros): Likewise
        * dwarf2/read.c (dwarf_decode_macros): Pass str_offsets_base in the parameters
        which is the value of DW_AT_str_offsets_base.
        * dwarf2/macro.h (dwarf_decode_macros): Modify the definition to include
        str_offsets_base.
        * macrotab.c (macro_lookup_inclusion): In DWARF version 5 filename
        includes the full directory path.
---
 gdb/dwarf2/macro.c | 72 ++++++++++++++++++++++++++++++++++++++++++++--
 gdb/dwarf2/macro.h |  3 ++
 gdb/dwarf2/read.c  | 21 +++++++++++++-
 gdb/macrotab.c     |  3 +-
 4 files changed, 94 insertions(+), 5 deletions(-)

diff --git a/gdb/dwarf2/macro.c b/gdb/dwarf2/macro.c
index d047d806f8..0fdc76a151 100644
--- a/gdb/dwarf2/macro.c
+++ b/gdb/dwarf2/macro.c
@@ -427,6 +427,9 @@ dwarf_decode_macro_bytes (dwarf2_per_objfile *per_objfile,
   const struct dwarf2_section_info *section,
   int section_is_gnu, int section_is_dwz,
   unsigned int offset_size,
+  struct dwarf2_section_info *str_section,
+  struct dwarf2_section_info *str_offsets_section,
+  ULONGEST str_offsets_base,
   htab_t include_hash)
 {
   struct objfile *objfile = per_objfile->objfile;
@@ -561,6 +564,54 @@ dwarf_decode_macro_bytes (dwarf2_per_objfile *per_objfile,
           }
           break;
 
+ case DW_MACRO_define_strx:
+ case DW_MACRO_undef_strx:
+  {
+    unsigned int bytes_read;
+
+    int line = read_unsigned_leb128 (abfd, mac_ptr, &bytes_read);
+    mac_ptr += bytes_read;
+    int offset_index = read_unsigned_leb128 (abfd, mac_ptr, &bytes_read);
+    mac_ptr += bytes_read;
+
+    str_offsets_section->read (objfile);
+    const gdb_byte *info_ptr = (str_offsets_section->buffer
+ + str_offsets_base
+ + offset_index * offset_size);
+
+    const char *macinfo_str = (macinfo_type == DW_MACRO_define_strx ?
+       "DW_MACRO_define_strx" : "DW_MACRO_undef_strx");
+
+    if (str_offsets_base + offset_index * offset_size
+ >= str_offsets_section->size)
+      complaint (_("%s pointing outside of .debug_str_offsets section "
+   "[in module %s]"), macinfo_str, objfile_name (objfile));
+
+    ULONGEST str_offset;
+    if (offset_size == 4)
+      str_offset = bfd_get_32 (abfd, info_ptr);
+    else
+      str_offset = bfd_get_64 (abfd, info_ptr);
+
+    const char *body = str_section->read_string (objfile, str_offset,
+ macinfo_str);
+    if (current_file == nullptr)
+      {
+ /* DWARF violation as no main source is present.  */
+ complaint (_("debug info with no main source gives macro %s "
+     "on line %d: %s"),
+     macinfo_type == DW_MACRO_define_strx ? _("definition")
+     : _("undefinition"), line, body);
+ break;
+      }
+
+    if (macinfo_type == DW_MACRO_define_strx)
+      parse_macro_definition (current_file, line, body);
+    else
+      macro_undef (current_file, line, body);
+   }
+   break;
+
         case DW_MACRO_start_file:
           {
             unsigned int bytes_read;
@@ -671,7 +722,8 @@ dwarf_decode_macro_bytes (dwarf2_per_objfile *per_objfile,
   new_mac_ptr, include_mac_end,
   current_file, lh, section,
   section_is_gnu, is_dwz, offset_size,
-  include_hash);
+  str_section, str_offsets_section,
+  str_offsets_base, include_hash);
 
  htab_remove_elt (include_hash, (void *) new_mac_ptr);
       }
@@ -712,7 +764,9 @@ dwarf_decode_macros (dwarf2_per_objfile *per_objfile,
      buildsym_compunit *builder,
      const dwarf2_section_info *section,
      const struct line_header *lh, unsigned int offset_size,
-     unsigned int offset, int section_is_gnu)
+     unsigned int offset, struct dwarf2_section_info *str_section,
+     struct dwarf2_section_info *str_offsets_section,
+     ULONGEST str_offsets_base, int section_is_gnu)
 {
   bfd *abfd;
   const gdb_byte *mac_ptr, *mac_end;
@@ -814,6 +868,17 @@ dwarf_decode_macros (dwarf2_per_objfile *per_objfile,
     mac_ptr += offset_size;
   }
   break;
+ case DW_MACRO_define_strx:
+ case DW_MACRO_undef_strx:
+  {
+    unsigned int bytes_read;
+
+    read_unsigned_leb128 (abfd, mac_ptr, &bytes_read);
+    mac_ptr += bytes_read;
+    read_unsigned_leb128 (abfd, mac_ptr, &bytes_read);
+    mac_ptr += bytes_read;
+  }
+  break;
 
  case DW_MACRO_import:
  case DW_MACRO_import_sup:
@@ -861,5 +926,6 @@ dwarf_decode_macros (dwarf2_per_objfile *per_objfile,
   *slot = (void *) mac_ptr;
   dwarf_decode_macro_bytes (per_objfile, builder, abfd, mac_ptr, mac_end,
     current_file, lh, section, section_is_gnu, 0,
-    offset_size, include_hash.get ());
+    offset_size, str_section, str_offsets_section,
+    str_offsets_base, include_hash.get ());
 }
diff --git a/gdb/dwarf2/macro.h b/gdb/dwarf2/macro.h
index d874068947..0a7ac55fc0 100644
--- a/gdb/dwarf2/macro.h
+++ b/gdb/dwarf2/macro.h
@@ -28,6 +28,9 @@ extern void dwarf_decode_macros (dwarf2_per_objfile *per_objfile,
  const struct line_header *lh,
  unsigned int offset_size,
  unsigned int offset,
+ dwarf2_section_info *str_section,
+ dwarf2_section_info *str_offsets_section,
+ ULONGEST str_offsets_base,
  int section_is_gnu);
 
 #endif /* GDB_DWARF2_MACRO_H */
diff --git a/gdb/dwarf2/read.c b/gdb/dwarf2/read.c
index 558fad74f8..845adb0325 100644
--- a/gdb/dwarf2/read.c
+++ b/gdb/dwarf2/read.c
@@ -23350,8 +23350,27 @@ dwarf_decode_macros (struct dwarf2_cu *cu, unsigned int offset,
 
   buildsym_compunit *builder = cu->get_builder ();
 
+  struct dwarf2_section_info *str_offsets_section;
+  struct dwarf2_section_info *str_section;
+  ULONGEST str_offsets_base;
+
+  if (cu->dwo_unit != nullptr)
+    {
+      str_offsets_section = &cu->dwo_unit->dwo_file
+       ->sections.str_offsets;
+      str_section = &cu->dwo_unit->dwo_file->sections.str;
+      str_offsets_base = cu->header.addr_size;
+    }
+  else
+    {
+      str_offsets_section = &per_objfile->per_bfd->str_offsets;
+      str_section = &per_objfile->per_bfd->str;
+      str_offsets_base = *cu->str_offsets_base;
+    }
+
   dwarf_decode_macros (per_objfile, builder, section, lh,
-       offset_size, offset, section_is_gnu);
+       offset_size, offset, str_section, str_offsets_section,
+       str_offsets_base, section_is_gnu);
 }
 
 /* Return the .debug_loc section to use for CU.
diff --git a/gdb/macrotab.c b/gdb/macrotab.c
index 9ada436eaf..4ffb2d67cb 100644
--- a/gdb/macrotab.c
+++ b/gdb/macrotab.c
@@ -507,7 +507,8 @@ struct macro_source_file *
 macro_lookup_inclusion (struct macro_source_file *source, const char *name)
 {
   /* Is SOURCE itself named NAME?  */
-  if (filename_cmp (name, source->filename) == 0)
+  if (filename_cmp (name, source->filename) == 0 ||
+      filename_cmp (basename (name), basename (source->filename)) == 0)
     return source;
 
   /* It's not us.  Try all our children, and return the lowest.  */
--
2.17.1