cmd/go, cmd/asm: pass -linkshared to assembler for shared linkage builds

When the -linkshared build mode is in effect, the Go command passes
the "-linkshared" command line option to the compiler so as to insure
special handling for things like builtin functions (which may appear
in a shared library and not the main executable). This patch extends
this behavior to the assembler, since the assembler may also wind up
referencing builtins when emitting a stack-split prolog.

Fixes #43107.

Change-Id: I56eaded79789b083f3c3d800fb140353dee33ba9
Reviewed-on: https://go-review.googlesource.com/c/go/+/276932
Trust: Than McIntosh <thanm@google.com>
Run-TryBot: Than McIntosh <thanm@google.com>
TryBot-Result: Go Bot <gobot@golang.org>
Reviewed-by: Jay Conrod <jayconrod@google.com>
Reviewed-by: Cherry Zhang <cherryyz@google.com>

src/cmd/asm/internal/flags/flags.go

@@ -20,6 +20,7 @@ var (
 	TrimPath         = flag.String("trimpath", "", "remove prefix from recorded source file paths")
 	Shared           = flag.Bool("shared", false, "generate code that can be linked into a shared library")
 	Dynlink          = flag.Bool("dynlink", false, "support references to Go symbols defined in other shared libraries")
+	Linkshared       = flag.Bool("linkshared", false, "generate code that will be linked against Go shared libraries")
 	AllErrors        = flag.Bool("e", false, "no limit on number of errors reported")
 	SymABIs          = flag.Bool("gensymabis", false, "write symbol ABI information to output file, don't assemble")
 	Importpath       = flag.String("p", "", "set expected package import to path")

src/cmd/asm/main.go

@@ -37,6 +37,7 @@ func main() {
 	ctxt := obj.Linknew(architecture.LinkArch)
 	ctxt.Debugasm = flags.PrintOut
 	ctxt.Flag_dynlink = *flags.Dynlink
+	ctxt.Flag_linkshared = *flags.Linkshared
 	ctxt.Flag_shared = *flags.Shared || *flags.Dynlink
 	ctxt.IsAsm = true
 	ctxt.Pkgpath = *flags.Importpath

src/cmd/go/internal/work/init.go

@@ -241,7 +241,8 @@ func buildModeInit() {
 		if gccgo {
 			codegenArg = "-fPIC"
 		} else {
-			forcedAsmflags = append(forcedAsmflags, "-D=GOBUILDMODE_shared=1")
+			forcedAsmflags = append(forcedAsmflags, "-D=GOBUILDMODE_shared=1",
+				"-linkshared")
 			codegenArg = "-dynlink"
 			forcedGcflags = append(forcedGcflags, "-linkshared")
 			// TODO(mwhudson): remove -w when that gets fixed in linker.