cmd/link: avoid bitcode incompatible flag -Wl,no_pie on darwin/arm

[eliasnaur]

CL 201358 removes most of the flags incompatible with -fembed-bitcode on iOS. However, -Wl,no_pie is left for darwin/arm because without it, linking fails:

ld: warning: PIE disabled. Absolute addressing (perhaps -mdynamic-no-pic) not allowed in code signed PIE, but used in _runtime.rodata from /var/folders/qq/qxn86k813bn9fjxydm095rxw0000gp/T/workdir-host-darwin-amd64-zenly-ios/tmp/go-link-225285265/go.o. To fix this warning, don't compile with -mdynamic-no-pic or link with -Wl,-no_pie

This error surprised @cherrymui who

thought we have removed absolute addressing on darwin/arm. Maybe we only did this for normal symbols but we missed runtime.rodata (which is linker generated)? I could take a look. (but probably not so soon...)

@thanm also expressed interest in digging into this:

The "runtime.rodata" thing seems odd -- runtime.rodata is a linker generated symbol, but looking at the linker code it appears to just be a pseudo-symbol that incorporates all of the rodata for the program. I ran a couple of regular builds on Darwin/amd64 with -buildmode=pie and looked over the relocations in the Go object file, and I don't see anything suspicious (although I'm not sure if that says much).

(from the golang-dev thread)

The error above is a build time error so can readily be reproduced on macOS with the following change applied:

diff --git a/src/cmd/link/internal/ld/lib.go b/src/cmd/link/internal/ld/lib.go
index d5868c9770..78f493ca9f 100644
--- a/src/cmd/link/internal/ld/lib.go
+++ b/src/cmd/link/internal/ld/lib.go
@@ -1206,7 +1206,7 @@ func (ctxt *Link) hostlink() {
        switch ctxt.BuildMode {
        case BuildModeExe:
                if ctxt.HeadType == objabi.Hdarwin {
-                       if ctxt.Arch.Family != sys.ARM64 {
+                       if !ctxt.Arch.InFamily(sys.ARM, sys.ARM64) {
                                argv = append(argv, "-Wl,-no_pie")
                        }
                        if !ctxt.Arch.InFamily(sys.ARM, sys.ARM64) {

[gopherbot]

Change https://golang.org/cl/205060 mentions this issue: cmd/link: enable PIE on darwin/arm