For a call to not return in to the stackmap shadow, the shadow must end with the call.
To do this, we must insert any required nops *before* the call, and not after it.
git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@220728
91177308-0d34-0410-b5e6-
96231b3b80d8
MCInst TmpInst;
MCInstLowering.Lower(MI, TmpInst);
MCInst TmpInst;
MCInstLowering.Lower(MI, TmpInst);
- EmitAndCountInstruction(TmpInst);
// Stackmap shadows cannot include branch targets, so we can count the bytes
// Stackmap shadows cannot include branch targets, so we can count the bytes
- // in a call towards the shadow, but must flush the shadow immediately after
- // to account for the return from the call.
- if (MI->isCall())
+ // in a call towards the shadow, but must ensure that the no thread returns
+ // in to the stackmap shadow. The only way to achieve this is if the call
+ // is at the end of the shadow.
+ if (MI->isCall()) {
+ // Count then size of the call towards the shadow
+ SMShadowTracker.count(TmpInst, getSubtargetInfo());
+ // Then flush the shadow so that we fill with nops before the call, not
+ // after it.
SMShadowTracker.emitShadowPadding(OutStreamer, getSubtargetInfo());
SMShadowTracker.emitShadowPadding(OutStreamer, getSubtargetInfo());
+ // Then emit the call
+ OutStreamer.EmitInstruction(TmpInst, getSubtargetInfo());
+ return;
+ }
+
+ EmitAndCountInstruction(TmpInst);
; bar. However, the frame teardown and the return do not count towards the
; stackmap shadow as the call return counts as a branch target so must flush
; the shadow.
; bar. However, the frame teardown and the return do not count towards the
; stackmap shadow as the call return counts as a branch target so must flush
; the shadow.
+; Note that in order for a thread to not return in to the patched space
+; the call must be at the end of the shadow, so the required nop must be
+; before the call, not after.
define void @shadow_optimization_test() {
entry:
; CHECK-LABEL: shadow_optimization_test:
; CHECK: callq _bar
define void @shadow_optimization_test() {
entry:
; CHECK-LABEL: shadow_optimization_test:
; CHECK: callq _bar
+; CHECK: nop
+; CHECK: callq _bar
; CHECK-NOT: nop
; CHECK: callq _bar
; CHECK-NOT: nop
; CHECK: callq _bar
-; CHECK: nop
-; CHECK: retq
call void @bar()
tail call void (i64, i32, ...)* @llvm.experimental.stackmap(i64 0, i32 8)
call void @bar()
call void @bar()
tail call void (i64, i32, ...)* @llvm.experimental.stackmap(i64 0, i32 8)
call void @bar()