[debug] Fix dwarf v4 .debug_macro.dwo

Consider a hello world, compiled with -gsplit-dwarf and dwarf version 4, and
-g3:
...
$ gcc -gdwarf-4 -gsplit-dwarf /data/vries/hello.c -g3 -save-temps -dA
...

In section .debug_macro.dwo, we have:
...
.Ldebug_macro0:
        .value  0x4     # DWARF macro version number
        .byte   0x2     # Flags: 32-bit, lineptr present
        .long   .Lskeleton_debug_line0
        .byte   0x3     # Start new file
        .uleb128 0      # Included from line number 0
        .uleb128 0x1    # file /data/vries/hello.c
        .byte   0x5     # Define macro strp
        .uleb128 0      # At line number 0
        .uleb128 0x1d0  # The macro: "__STDC__ 1"
...

Given that we use a DW_MACRO_define_strp, we'd expect 0x1d0 to be an
offset into a .debug_str.dwo section.

But in fact, 0x1d0 is an index into the string offset table in
section .debug_str_offsets.dwo:
...
        .long   0x34f0  # indexed string 0x1d0: __STDC__ 1
...

Add asserts that catch this inconsistency, and fix this by using
DW_MACRO_define_strx instead.

Tested on x86_64.

gcc/ChangeLog:

2024-05-14  Tom de Vries  <tdevries@suse.de>

	PR debug/115066
	* dwarf2out.cc (output_macinfo_op): Fix DW_MACRO_define_strx/strp
	choice for v4 .debug_macro.dwo.  Add asserts to check that choice.

gcc/testsuite/ChangeLog:

2024-05-14  Tom de Vries  <tdevries@suse.de>

	PR debug/115066
	* gcc.dg/pr115066.c: New test.

2 files changed, 22 insertions, 6 deletions

diff --git a/gcc/dwarf2out.cc b/gcc/dwarf2out.cc
index eedb13b..70b7f5f 100644
--- a/gcc/dwarf2out.cc
+++ b/gcc/dwarf2out.cc
@@ -29045,7 +29045,7 @@ output_macinfo_op (macinfo_entry *ref)
 	  && !DWARF2_INDIRECT_STRING_SUPPORT_MISSING_ON_TARGET
 	  && (debug_str_section->common.flags & SECTION_MERGE) != 0)
 	{
-	  if (dwarf_split_debug_info && dwarf_version >= 5)
+	  if (dwarf_split_debug_info)
 	    ref->code = ref->code == DW_MACINFO_define
 			? DW_MACRO_define_strx : DW_MACRO_undef_strx;
 	  else
@@ -29097,12 +29097,20 @@ output_macinfo_op (macinfo_entry *ref)
 				   HOST_WIDE_INT_PRINT_UNSIGNED,
 				   ref->lineno);
       if (node->form == DW_FORM_strp)
-        dw2_asm_output_offset (dwarf_offset_size, node->label,
-                               debug_str_section, "The macro: \"%s\"",
-                               ref->info);
+	{
+	  gcc_assert (ref->code == DW_MACRO_define_strp
+		      || ref->code == DW_MACRO_undef_strp);
+	  dw2_asm_output_offset (dwarf_offset_size, node->label,
+				 debug_str_section, "The macro: \"%s\"",
+				 ref->info);
+	}
       else
-        dw2_asm_output_data_uleb128 (node->index, "The macro: \"%s\"",
-                                     ref->info);
+	{
+	  gcc_assert (ref->code == DW_MACRO_define_strx
+		      || ref->code == DW_MACRO_undef_strx);
+	  dw2_asm_output_data_uleb128 (node->index, "The macro: \"%s\"",
+				       ref->info);
+	}
       break;
     case DW_MACRO_import:
       dw2_asm_output_data (1, ref->code, "Import");
diff --git a/gcc/testsuite/gcc.dg/pr115066.c b/gcc/testsuite/gcc.dg/pr115066.c
new file mode 100644
index 0000000..645757d
--- /dev/null
+++ b/gcc/testsuite/gcc.dg/pr115066.c
@@ -0,0 +1,8 @@
+/* { dg-do compile } */
+/* { dg-skip-if "split DWARF unsupported" { hppa*-*-hpux* powerpc*-ibm-aix* *-*-darwin* } } */
+/* { dg-options "-gsplit-dwarf -g3 -dA -gdwarf-4" } */
+/* { dg-final { scan-assembler-times {\.section\t"?\.debug_macro} 1 } } */
+/* { dg-final { scan-assembler-not {\.byte\t0x5\t# Define macro strp} } } */
+/* { dg-final { scan-assembler {\.byte\t0xb\t# Define macro strx} } } */
+
+#define foo 1