cmd/link, runtime: arm implementation of addmoduledata

Change-Id: I3975e10c2445e23c2798a7203a877ff2de3427c7
Reviewed-on: https://go-review.googlesource.com/14189Reviewed-by: Ian Lance Taylor <iant@golang.org>

src/cmd/link/internal/arm/asm.go

@@ -37,7 +37,75 @@ import (
 	"log"
 )
 
+// This assembler:
+//
+//         .align 2
+// local.dso_init:
+//         ldr r0, .Lmoduledata
+// .Lloadfrom:
+//         ldr r0, [r0]
+//         b runtime.addmoduledata@plt
+// .align 2
+// .Lmoduledata:
+//         .word local.moduledata(GOT_PREL) + (. - (.Lloadfrom + 4))
+// assembles to:
+//
+// 00000000 <local.dso_init>:
+//    0:        e59f0004        ldr     r0, [pc, #4]    ; c <local.dso_init+0xc>
+//    4:        e5900000        ldr     r0, [r0]
+//    8:        eafffffe        b       0 <runtime.addmoduledata>
+//                      8: R_ARM_JUMP24 runtime.addmoduledata
+//    c:        00000004        .word   0x00000004
+//                      c: R_ARM_GOT_PREL       local.moduledata
+
 func gentext() {
+	if !ld.DynlinkingGo() {
+		return
+	}
+	addmoduledata := ld.Linklookup(ld.Ctxt, "runtime.addmoduledata", 0)
+	if addmoduledata.Type == obj.STEXT {
+		// we're linking a module containing the runtime -> no need for
+		// an init function
+		return
+	}
+	addmoduledata.Reachable = true
+	initfunc := ld.Linklookup(ld.Ctxt, "go.link.addmoduledata", 0)
+	initfunc.Type = obj.STEXT
+	initfunc.Local = true
+	initfunc.Reachable = true
+	o := func(op uint32) {
+		ld.Adduint32(ld.Ctxt, initfunc, op)
+	}
+	o(0xe59f0004)
+	o(0xe08f0000)
+
+	o(0xeafffffe)
+	rel := ld.Addrel(initfunc)
+	rel.Off = 8
+	rel.Siz = 4
+	rel.Sym = ld.Linklookup(ld.Ctxt, "runtime.addmoduledata", 0)
+	rel.Type = obj.R_CALLARM
+	rel.Add = 0xeafffffe // vomit
+
+	o(0x00000000)
+	rel = ld.Addrel(initfunc)
+	rel.Off = 12
+	rel.Siz = 4
+	rel.Sym = ld.Ctxt.Moduledata
+	rel.Type = obj.R_PCREL
+	rel.Add = 4
+
+	if ld.Ctxt.Etextp != nil {
+		ld.Ctxt.Etextp.Next = initfunc
+	} else {
+		ld.Ctxt.Textp = initfunc
+	}
+	ld.Ctxt.Etextp = initfunc
+	initarray_entry := ld.Linklookup(ld.Ctxt, "go.link.addmoduledatainit", 0)
+	initarray_entry.Reachable = true
+	initarray_entry.Local = true
+	initarray_entry.Type = obj.SINITARR
+	ld.Addaddr(ld.Ctxt, initarray_entry, initfunc)
 }
 
 // Preserve highest 8 bits of a, and do addition to lower 24-bit
@@ -228,6 +296,13 @@ func elfreloc1(r *ld.Reloc, sectoff int64) int {
 
 	case obj.R_TLS_IE:
 		ld.Thearch.Lput(ld.R_ARM_TLS_IE32 | uint32(elfsym)<<8)
+
+	case obj.R_GOTPCREL:
+		if r.Siz == 4 {
+			ld.Thearch.Lput(ld.R_ARM_GOT_PREL | uint32(elfsym)<<8)
+		} else {
+			return -1
+		}
 	}
 
 	return 0

src/runtime/asm_arm.s

@@ -1076,3 +1076,14 @@ TEXT runtime·usplitR0(SB),NOSPLIT,$0
 
 TEXT runtime·sigreturn(SB),NOSPLIT,$0-4
         RET
+
+#ifndef GOOS_nacl
+// This is called from .init_array and follows the platform, not Go, ABI.
+TEXT runtime·addmoduledata(SB),NOSPLIT,$0-4
+	MOVW	R9, saver9-4(SP) // The access to global variables below implicitly uses R9, which is callee-save
+	MOVW	runtime·lastmoduledatap(SB), R1
+	MOVW	R0, moduledata_next(R1)
+	MOVW	R0, runtime·lastmoduledatap(SB)
+	MOVW	saver9-4(SP), R9
+	RET
+#endif