cmd/asm: report an error when trying to do spectre on 386

The compiler refuses to do spectre mitigation on 386, but the
assembler doesn't. Fix that.

Fixes #49006

Change-Id: I887b6f7ed7523a47f463706f06ca4c2c6e828b6b
Reviewed-on: https://go-review.googlesource.com/c/go/+/356190
Trust: Keith Randall <khr@golang.org>
Run-TryBot: Keith Randall <khr@golang.org>
TryBot-Result: Go Bot <gobot@golang.org>
Reviewed-by: Bryan C. Mills <bcmills@google.com>

diff --git a/src/cmd/internal/obj/x86/asm6.go b/src/cmd/internal/obj/x86/asm6.go
index 43ce832b179629878815a0349c53d75a0836bed9..6555756fd3b06f27e7c8761c520b7c2006dd4ba6 100644 (file)
--- a/src/cmd/internal/obj/x86/asm6.go
+++ b/src/cmd/internal/obj/x86/asm6.go
@@ -2035,6 +2035,11 @@ type nopPad struct {
 }
 
 func span6(ctxt *obj.Link, s *obj.LSym, newprog obj.ProgAlloc) {
+       if ctxt.Retpoline && ctxt.Arch.Family == sys.I386 {
+               ctxt.Diag("-spectre=ret not supported on 386")
+               ctxt.Retpoline = false // don't keep printing
+       }
+
        pjc := makePjcCtx(ctxt)
 
        if s.P != nil {