cmd/objdump: pass the correct execution mode to x86asm.Decode in disasm_x86 on 386

Fixes #22093
Fixes #19988

Change-Id: Ibd8ec89e091fd527f363999e484676931d7aa6e2
Reviewed-on: https://go-review.googlesource.com/67450Reviewed-by: Keith Randall <khr@golang.org>
Run-TryBot: Keith Randall <khr@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>

src/cmd/internal/objfile/disasm.go

@@ -304,7 +304,7 @@ func disasm_amd64(code []byte, pc uint64, lookup lookupFunc, _ binary.ByteOrder)
 }
 
 func disasm_x86(code []byte, pc uint64, lookup lookupFunc, arch int) (string, int) {
-	inst, err := x86asm.Decode(code, 64)
+	inst, err := x86asm.Decode(code, arch)
 	var text string
 	size := inst.Len
 	if err != nil || size == 0 || inst.Op == 0 {

src/cmd/objdump/objdump_test.go

@@ -148,6 +148,13 @@ func testDisasm(t *testing.T, printCode bool, flags ...string) {
 			ok = false
 		}
 	}
+	if goarch == "386" {
+		if strings.Contains(text, "(IP)") {
+			t.Errorf("disassembly contains PC-Relative addressing on 386")
+			ok = false
+		}
+	}
+
 	if !ok {
 		t.Logf("full disassembly:\n%s", text)
 	}
@@ -234,6 +241,12 @@ func TestDisasmGoobj(t *testing.T) {
 			ok = false
 		}
 	}
+	if runtime.GOARCH == "386" {
+		if strings.Contains(text, "(IP)") {
+			t.Errorf("disassembly contains PC-Relative addressing on 386")
+			ok = false
+		}
+	}
 	if !ok {
 		t.Logf("full disassembly:\n%s", text)
 	}