[PATCH] D73760: [X86] -fpatchable-function-entry=N,0: place patch label after ENDBR{32,64}

[Fangrui Song via Phabricator via llvm-commits]

MaskRay created this revision.
MaskRay added reviewers: mrutland, nickdesaulniers, nsz.
Herald added subscribers: llvm-commits, hiraditya, kristof.beyls.
Herald added a project: LLVM.

Similar to D73680 <https://reviews.llvm.org/D73680> (AArch64 BTI).


Repository:
  rG LLVM Github Monorepo

https://reviews.llvm.org/D73760

Files:
  llvm/lib/Target/X86/X86MCInstLower.cpp
  llvm/test/CodeGen/X86/patchable-function-entry-ibt.ll


Index: llvm/test/CodeGen/X86/patchable-function-entry-ibt.ll
===================================================================
--- llvm/test/CodeGen/X86/patchable-function-entry-ibt.ll
+++ llvm/test/CodeGen/X86/patchable-function-entry-ibt.ll
@@ -15,12 +15,14 @@
 define void @f1() "patchable-function-entry"="1" {
 ; CHECK-LABEL: f1:
 ; CHECK-NEXT: .Lfunc_begin1:
-; CHECK:       endbr64
+; CHECK:      # %bb.0:
+; CHECK-NEXT:  endbr64
+; CHECK-NEXT: .Lpatch0:
 ; CHECK-NEXT:  nop
 ; CHECK-NEXT:  retq
 ; CHECK:      .section __patchable_function_entries,"awo", at progbits,f1,unique,0
 ; CHECK-NEXT: .p2align 3
-; CHECK-NEXT: .quad .Lfunc_begin1
+; CHECK-NEXT: .quad .Lpatch0
   ret void
 }
 
@@ -43,6 +45,30 @@
   ret void
 }
 
+;; -fpatchable-function-entry=1 -fcf-protection=branch
+;; For M=0, don't create .Lpatch0 if the initial instruction is not ENDBR,
+;; even if other basic blocks may have ENDBR.
+ at buf = internal global [5 x i8*] zeroinitializer
+declare i8* @llvm.frameaddress(i32)
+declare i8* @llvm.stacksave()
+declare i32 @llvm.eh.sjlj.setjmp(i8*)
+
+define internal void @f1i() "patchable-function-entry"="1" {
+; CHECK-LABEL: f1i:
+; CHECK-NEXT: .Lfunc_begin3:
+; CHECK:      # %bb.0:
+; CHECK-NEXT:  nop
+; CHECK-NEXT:  pushq %rbp
+;; Another basic block has ENDBR, but it doesn't affect our decision to not create .Lpatch0
+; CHECK:       endbr64
+; CHECK:      .section __patchable_function_entries,"awo", at progbits,f1,unique,0
+; CHECK-NEXT: .p2align 3
+; CHECK-NEXT: .quad .Lfunc_begin3
+entry:
+  tail call i32 @llvm.eh.sjlj.setjmp(i8* bitcast ([5 x i8*]* @buf to i8*))
+  ret void
+}
+
 !llvm.module.flags = !{!0}
 
 !0 = !{i32 4, !"cf-protection-branch", i32 1}
Index: llvm/lib/Target/X86/X86MCInstLower.cpp
===================================================================
--- llvm/lib/Target/X86/X86MCInstLower.cpp
+++ llvm/lib/Target/X86/X86MCInstLower.cpp
@@ -2005,6 +2005,25 @@
     break;
   }
 
+  case X86::ENDBR32:
+  case X86::ENDBR64: {
+    // CurrentPatchableFunctionEntrySym can be CurrentFnBegin only for
+    // -fpatchable-function-entry=N,0. The entry MBB is guaranteed to be
+    // non-empty. If MI is the initial ENDBR, place the
+    // __patchable_function_entries label after ENDBR.
+    if (CurrentPatchableFunctionEntrySym &&
+        CurrentPatchableFunctionEntrySym == CurrentFnBegin &&
+        MI == &MF->front().front()) {
+      MCInst Inst;
+      MCInstLowering.Lower(MI, Inst);
+      EmitAndCountInstruction(Inst);
+      CurrentPatchableFunctionEntrySym = createTempSymbol("patch");
+      OutStreamer->EmitLabel(CurrentPatchableFunctionEntrySym);
+      return;
+    }
+    break;
+  }
+
   case X86::TAILJMPr:
   case X86::TAILJMPm:
   case X86::TAILJMPd:


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