DWARFv5: Handle DW_MACRO_define_strx and DW_MACRO_undef_strx macro entries.

GDB complaints "During symbol reading: unrecognized DW_MACFINO
opcode 0xb" with the testcase given below. 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/new_gdb/binutils-gdb/build/bin/gdb -q macro.out -ex "set complaints 1" -ex "start"
Reading symbols from macro.out...
During symbol reading: unrecognized DW_MACFINO opcode 0xb
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;
(gdb)

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.

1 files changed, 20 insertions, 1 deletions

diff --git a/gdb/dwarf2/read.c b/gdb/dwarf2/read.c
index 973a375..eedfea1 100644
--- a/gdb/dwarf2/read.c
+++ b/gdb/dwarf2/read.c
@@ -23900,8 +23900,27 @@ 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.