cmd/internal/dwarf: update to DWARF4, emit frame_base

In preparation for CL 41770, upgrade .debug_info to DWARF4, and emit
DW_AT_frame_base on subprograms. This should make no semantic
difference.

Also fix a long-standing bug/inconsistency in puttattr: it didn't
add the addend to ref_addrs. Previously this didn't matter because it
was only used for types, but now it's used for section offsets into
symbols that have multiple entries.

RELNOTE=yes

Change-Id: Ib10654ac92edfa29c5167c44133648151d70cf76
Reviewed-on: https://go-review.googlesource.com/44210
Reviewed-by: Hyang-Ah Hana Kim <hyangah@gmail.com>

src/cmd/internal/dwarf/dwarf.go

@@ -255,7 +255,7 @@ var abbrevs = [DW_NABRV]dwAbbrev{
 			{DW_AT_language, DW_FORM_data1},
 			{DW_AT_low_pc, DW_FORM_addr},
 			{DW_AT_high_pc, DW_FORM_addr},
-			{DW_AT_stmt_list, DW_FORM_data4},
+			{DW_AT_stmt_list, DW_FORM_sec_offset},
 			{DW_AT_comp_dir, DW_FORM_string},
 			{DW_AT_producer, DW_FORM_string},
 		},
@@ -269,6 +269,7 @@ var abbrevs = [DW_NABRV]dwAbbrev{
 			{DW_AT_name, DW_FORM_string},
 			{DW_AT_low_pc, DW_FORM_addr},
 			{DW_AT_high_pc, DW_FORM_addr},
+			{DW_AT_frame_base, DW_FORM_block1},
 			{DW_AT_external, DW_FORM_flag},
 		},
 	},
@@ -306,13 +307,12 @@ var abbrevs = [DW_NABRV]dwAbbrev{
 			{DW_AT_type, DW_FORM_ref_addr},
 		},
 	},
-
 	/* LEXICAL_BLOCK_RANGES */
 	{
 		DW_TAG_lexical_block,
 		DW_CHILDREN_yes,
 		[]dwAttrForm{
-			{DW_AT_ranges, DW_FORM_data4}, // replace with DW_FORM_sec_offset in DWARFv4.
+			{DW_AT_ranges, DW_FORM_sec_offset},
 		},
 	},
 
@@ -634,14 +634,15 @@ func putattr(ctxt Context, s Sym, abbrev int, form int, cls int, value int64, da
 			ctxt.AddInt(s, 1, 0)
 		}
 
-	// In DWARF 3 the ref_addr is always 32 bits, unless emitting a large
+	// As of DWARF 3 the ref_addr is always 32 bits, unless emitting a large
 	// (> 4 GB of debug info aka "64-bit") unit, which we don't implement.
 	case DW_FORM_ref_addr: // reference to a DIE in the .info section
+		fallthrough
+	case DW_FORM_sec_offset: // offset into a DWARF section other than .info
 		if data == nil {
 			return fmt.Errorf("dwarf: null reference in %d", abbrev)
-		} else {
-			ctxt.AddSectionOffset(s, 4, data, 0)
 		}
+		ctxt.AddSectionOffset(s, 4, data, value)
 
 	case DW_FORM_ref1, // reference within the compilation unit
 		DW_FORM_ref2,      // reference
@@ -687,7 +688,8 @@ func PutFunc(ctxt Context, s, ranges Sym, name string, external bool, startPC Sy
 	Uleb128put(ctxt, s, DW_ABRV_FUNCTION)
 	putattr(ctxt, s, DW_ABRV_FUNCTION, DW_FORM_string, DW_CLS_STRING, int64(len(name)), name)
 	putattr(ctxt, s, DW_ABRV_FUNCTION, DW_FORM_addr, DW_CLS_ADDRESS, 0, startPC)
-	putattr(ctxt, s, DW_ABRV_FUNCTION, DW_FORM_addr, DW_CLS_ADDRESS, size+ctxt.SymValue(startPC), startPC)
+	putattr(ctxt, s, DW_ABRV_FUNCTION, DW_FORM_addr, DW_CLS_ADDRESS, size, startPC)
+	putattr(ctxt, s, DW_ABRV_FUNCTION, DW_FORM_block1, DW_CLS_BLOCK, 1, []byte{DW_OP_call_frame_cfa})
 	var ev int64
 	if external {
 		ev = 1
@@ -722,7 +724,7 @@ func putscope(ctxt Context, s, ranges Sym, startPC Sym, curscope int32, scopes [
 			putattr(ctxt, s, DW_ABRV_LEXICAL_BLOCK_SIMPLE, DW_FORM_addr, DW_CLS_ADDRESS, scope.Ranges[0].End, startPC)
 		} else {
 			Uleb128put(ctxt, s, DW_ABRV_LEXICAL_BLOCK_RANGES)
-			putattr(ctxt, s, DW_ABRV_LEXICAL_BLOCK_RANGES, DW_FORM_data4, DW_CLS_PTR, ranges.Len(), ranges)
+			putattr(ctxt, s, DW_ABRV_LEXICAL_BLOCK_RANGES, DW_FORM_sec_offset, DW_CLS_PTR, ranges.Len(), ranges)
 
 			ctxt.AddAddress(ranges, nil, -1)
 			ctxt.AddAddress(ranges, startPC, 0)

src/cmd/internal/dwarf/dwarf_defs.go

@@ -212,6 +212,11 @@ const (
 	DW_FORM_ref8      = 0x14 // reference
 	DW_FORM_ref_udata = 0x15 // reference
 	DW_FORM_indirect  = 0x16 // (see Section 7.5.3)
+	// Dwarf4
+	DW_FORM_sec_offset   = 0x17 // lineptr, loclistptr, macptr, rangelistptr
+	DW_FORM_exprloc      = 0x18 // exprloc
+	DW_FORM_flag_present = 0x19 // flag
+	DW_FORM_ref_sig8     = 0x20 // reference
 )
 
 // Table 24 (#operands, notes)

src/cmd/link/internal/ld/dwarf.go

@@ -1348,7 +1348,7 @@ func writeinfo(ctxt *Link, syms []*Symbol, funcs []*Symbol) []*Symbol {
 		// Fields marked with (*) must be changed for 64-bit dwarf
 		// This must match COMPUNITHEADERSIZE above.
 		Adduint32(ctxt, s, 0) // unit_length (*), will be filled in later.
-		Adduint16(ctxt, s, 3) // dwarf version (appendix F)
+		Adduint16(ctxt, s, 4) // dwarf version (appendix F)
 
 		// debug_abbrev_offset (*)
 		adddwarfref(ctxt, s, abbrevsym, 4)