cmd/link: unify text segment write

Currently we have two code paths of writing the text segment. They
are semantically the same:

- if we split text sections, we write all ".text" sections as
  text and the the rest as data.
- if we do not split text sections, we write the first section
  as text and the rest as data. The first section is named ".text"
  and is the only one in this case.

Unify the code.

Change-Id: Ic639eed625615be3c8a8d41f5b47e901552f587a
Reviewed-on: https://go-review.googlesource.com/c/go/+/316049
Trust: Cherry Zhang <cherryyz@google.com>
Reviewed-by: Than McIntosh <thanm@google.com>

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

@@ -29,8 +29,6 @@ func asmb(ctxt *Link) {
 	}
 
 	var wg sync.WaitGroup
-	sect := Segtext.Sections[0]
-	offset := sect.Vaddr - Segtext.Vaddr + Segtext.Fileoff
 	f := func(ctxt *Link, out *OutBuf, start, length int64) {
 		pad := thearch.CodePad
 		if pad == nil {
@@ -39,24 +37,15 @@ func asmb(ctxt *Link) {
 		CodeblkPad(ctxt, out, start, length, pad)
 	}
 
-	if !thearch.WriteTextBlocks {
-		writeParallel(&wg, f, ctxt, offset, sect.Vaddr, sect.Length)
-		for _, sect := range Segtext.Sections[1:] {
-			offset := sect.Vaddr - Segtext.Vaddr + Segtext.Fileoff
-			writeParallel(&wg, datblk, ctxt, offset, sect.Vaddr, sect.Length)
-		}
-	} else {
-		// TODO why can't we handle all sections this way?
 	for _, sect := range Segtext.Sections {
 		offset := sect.Vaddr - Segtext.Vaddr + Segtext.Fileoff
-			// Handle additional text sections with Codeblk
+		// Handle text sections with Codeblk
 		if sect.Name == ".text" {
 			writeParallel(&wg, f, ctxt, offset, sect.Vaddr, sect.Length)
 		} else {
 			writeParallel(&wg, datblk, ctxt, offset, sect.Vaddr, sect.Length)
 		}
 	}
-	}
 
 	if Segrodata.Filelen > 0 {
 		writeParallel(&wg, datblk, ctxt, Segrodata.Fileoff, Segrodata.Vaddr, Segrodata.Filelen)

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

@@ -203,9 +203,6 @@ type Arch struct {
 	// are padded with zeros.
 	CodePad []byte
 
-	// Set to true to write all text blocks in with CodeBlkWrite
-	WriteTextBlocks bool
-
 	// Plan 9 variables.
 	Plan9Magic  uint32
 	Plan9_64Bit bool

src/cmd/link/internal/ppc64/obj.go

@@ -50,7 +50,6 @@ func Init() (*sys.Arch, ld.Arch) {
 		Dwarfregsp: dwarfRegSP,
 		Dwarfreglr: dwarfRegLR,
 		TrampLimit: 0x1c00000,
-		WriteTextBlocks: true,
 
 		Adddynrel:        adddynrel,
 		Archinit:         archinit,