cmd/link: suppress -bind_at_load deprecation warning for ld-prime

ld-prime emits a deprecation warning for -bind_at_load. The flag
is needed for plugins to not deadlock (golang#38824) when linking with
older darwin linker. It is supposedly not needed with newer linker
when chained fixups are used. For now, we always pass it, and
suppress the warning.

For golang#61229.

Change-Id: I4b8a6f864a460c40dc38adbb533f664f7fd5343c
Reviewed-on: https://go-review.googlesource.com/c/go/+/508696
Reviewed-by: Than McIntosh <[email protected]>
TryBot-Result: Gopher Robot <[email protected]>
Run-TryBot: Cherry Mui <[email protected]>

Author: cherrymui

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

@@ -1903,6 +1903,16 @@ func (ctxt *Link) hostlink() {
 				out = append(out[:i], out[i+len(noPieWarning):]...)
 			}
 		}
+		if ctxt.IsDarwin() {
+			const bindAtLoadWarning = "ld: warning: -bind_at_load is deprecated on macOS\n"
+			if i := bytes.Index(out, []byte(bindAtLoadWarning)); i >= 0 {
+				// -bind_at_load is deprecated with ld-prime, but needed for
+				// correctness with older versions of ld64. Swallow the warning.
+				// TODO: maybe pass -bind_at_load conditionally based on C
+				// linker version.
+				out = append(out[:i], out[i+len(bindAtLoadWarning):]...)
+			}
+		}
 		ctxt.Logf("%s", out)
 	}