runtime: darwin/386 entrypoint for c-archive

Change-Id: Ic22597b5e2824cffe9598cb9b506af3426c285fd
Reviewed-on: https://go-review.googlesource.com/12412
Run-TryBot: David Crawshaw <crawshaw@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Ian Lance Taylor <iant@golang.org>

src/cmd/dist/test.go

@@ -573,7 +573,7 @@ func (t *tester) supportedBuildmode(mode string) bool {
 			return false
 		}
 		switch pair {
-		case "darwin-amd64", "darwin-arm", "darwin-arm64",
+		case "darwin-386", "darwin-amd64", "darwin-arm", "darwin-arm64",
 			"linux-amd64", "linux-386":
 			return true
 		}

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

@@ -444,7 +444,7 @@ func Asmbmacho() {
 		ms = newMachoSeg("", 40)
 
 		ms.fileoffset = Segtext.Fileoff
-		if Thearch.Thechar == '5' {
+		if Thearch.Thechar == '5' || Buildmode == BuildmodeCArchive {
 			ms.filesize = Segdata.Fileoff + Segdata.Filelen - Segtext.Fileoff
 		} else {
 			ms.filesize = Segdwarf.Fileoff + Segdwarf.Filelen - Segtext.Fileoff

src/runtime/rt0_darwin_386.s

@@ -12,5 +12,60 @@ TEXT _rt0_386_darwin(SB),NOSPLIT,$8
 	CALL	main(SB)
 	INT	$3
 
+// With -buildmode=c-archive, this symbol is called from a global constructor.
+TEXT _rt0_386_darwin_lib(SB),NOSPLIT,$0
+	PUSHL	BP
+	MOVL	SP, BP
+	PUSHL	BX
+	PUSHL	SI
+	PUSHL	DI
+
+	MOVL	8(BP), AX
+	MOVL	AX, _rt0_386_darwin_lib_argc<>(SB)
+	MOVL	12(BP), AX
+	MOVL	AX, _rt0_386_darwin_lib_argv<>(SB)
+
+	SUBL	$12, SP
+
+	// Create a new thread to do the runtime initialization and return.
+	MOVL	_cgo_sys_thread_create(SB), AX
+	TESTL	AX, AX
+	JZ	nocgo
+	MOVL	$_rt0_386_darwin_lib_go(SB), BX
+	MOVL	BX, 0(SP)
+	MOVL	$0, 4(SP)
+	CALL	AX
+	JMP     restore
+
+nocgo:
+	MOVL	$0x800000, 0(SP)               // stacksize = 8192KB
+	MOVL	$_rt0_386_darwin_lib_go(SB), AX
+	MOVL	AX, 4(SP)                      // fn
+	MOVL	$0, 8(SP)                      // fnarg
+	MOVL	$runtime·newosproc0(SB), AX
+	CALL	AX
+
+restore:
+	ADDL	$12, SP
+	POPL	DI
+	POPL	SI
+	POPL	BX
+	POPL	BP
+	RET
+
+TEXT _rt0_386_darwin_lib_go(SB),NOSPLIT,$12
+	MOVL	_rt0_386_darwin_lib_argc<>(SB), AX
+	MOVL	AX, 0(SP)
+	MOVL	_rt0_386_darwin_lib_argv<>(SB), AX
+	MOVL	AX, 4(SP)
+	MOVL	$runtime·rt0_go(SB), AX
+	CALL	AX
+	RET
+
+DATA _rt0_386_darwin_lib_argc<>(SB)/4, $0
+GLOBL _rt0_386_darwin_lib_argc<>(SB),NOPTR, $4
+DATA _rt0_386_darwin_lib_argv<>(SB)/4, $0
+GLOBL _rt0_386_darwin_lib_argv<>(SB),NOPTR, $4
+
 TEXT main(SB),NOSPLIT,$0
 	JMP	runtime·rt0_go(SB)