[PATCH] D89032: [WebAssembly] Handle indirect uses of longjmp

[Heejin Ahn via Phabricator via llvm-commits]

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In LowerEmscriptenEHSjLj, `longjmp` used to be replaced with
`emscripten_longjmp_jmpbuf(jmp_buf*, i32)`, which will eventually be
lowered to `emscripten_longjmp(i32, i32)`. The reason we used two
different names was because they had different signatures in the IR
pass.

D88697 <https://reviews.llvm.org/D88697> fixed this by only using `emscripten_longjmp(i32, i32)` and
adding a `ptrtoint` cast to its first argument, so

  longjmp(buf, 0)

becomes

  emscripten_longjmp((i32)buf, 0)

But this assumed all uses of `longjmp` was a direct call to it, which
was not the case. This patch handles indirect uses of `longjmp` by
replacing

  longjmp(buf, 0)

with

  (int(*)(jmp_buf*, int))emscripten_longjmp


Repository:
  rG LLVM Github Monorepo

https://reviews.llvm.org/D89032

Files:
  llvm/lib/Target/WebAssembly/WebAssemblyLowerEmscriptenEHSjLj.cpp
  llvm/test/CodeGen/WebAssembly/lower-em-sjlj.ll


Index: llvm/test/CodeGen/WebAssembly/lower-em-sjlj.ll
===================================================================
--- llvm/test/CodeGen/WebAssembly/lower-em-sjlj.ll
+++ llvm/test/CodeGen/WebAssembly/lower-em-sjlj.ll
@@ -11,6 +11,8 @@
 ; NO-TLS-DAG: __threwValue = external global i32
 ; TLS-DAG: __THREW__ = external thread_local(localexec) global i32
 ; TLS-DAG: __threwValue = external thread_local(localexec) global i32
+ at global_longjmp_ptr = global void (%struct.__jmp_buf_tag*, i32)* @longjmp, align 4
+; CHECK-DAG: @global_longjmp_ptr = global void (%struct.__jmp_buf_tag*, i32)* bitcast (void (i32, i32)* @emscripten_longjmp to void (%struct.__jmp_buf_tag*, i32)*)
 
 ; Test a simple setjmp - longjmp sequence
 define void @setjmp_longjmp() {
@@ -250,6 +252,36 @@
   ; CHECK: %var[[VARNO]] = phi i32 [ %var, %for.inc ]
 }
 
+; Tests cases where longjmp function pointer is used in other ways than direct
+; calls. longjmps should be replaced with
+; (int(*)(jmp_buf*, int))emscripten_longjmp.
+declare void @take_longjmp(void (%struct.__jmp_buf_tag*, i32)* %arg_ptr)
+define void @indirect_longjmp() {
+; CHECK-LABEL: @indirect_longjmp
+entry:
+  %local_longjmp_ptr = alloca void (%struct.__jmp_buf_tag*, i32)*, align 4
+  %buf0 = alloca [1 x %struct.__jmp_buf_tag], align 16
+  %buf1 = alloca [1 x %struct.__jmp_buf_tag], align 16
+
+  ; Store longjmp in a local variable, load it, and call it
+  store void (%struct.__jmp_buf_tag*, i32)* @longjmp, void (%struct.__jmp_buf_tag*, i32)** %local_longjmp_ptr, align 4
+  ; CHECK: store void (%struct.__jmp_buf_tag*, i32)* bitcast (void (i32, i32)* @emscripten_longjmp to void (%struct.__jmp_buf_tag*, i32)*), void (%struct.__jmp_buf_tag*, i32)** %local_longjmp_ptr, align 4
+  %longjmp_from_local_ptr = load void (%struct.__jmp_buf_tag*, i32)*, void (%struct.__jmp_buf_tag*, i32)** %local_longjmp_ptr, align 4
+  %arraydecay = getelementptr inbounds [1 x %struct.__jmp_buf_tag], [1 x %struct.__jmp_buf_tag]* %buf0, i32 0, i32 0
+  call void %longjmp_from_local_ptr(%struct.__jmp_buf_tag* %arraydecay, i32 0)
+
+  ; Load longjmp from a global variable and call it
+  %longjmp_from_global_ptr = load void (%struct.__jmp_buf_tag*, i32)*, void (%struct.__jmp_buf_tag*, i32)** @global_longjmp_ptr, align 4
+  %arraydecay1 = getelementptr inbounds [1 x %struct.__jmp_buf_tag], [1 x %struct.__jmp_buf_tag]* %buf1, i32 0, i32 0
+  call void %longjmp_from_global_ptr(%struct.__jmp_buf_tag* %arraydecay1, i32 0)
+
+  ; Pass longjmp as a function argument. This is a call but longjmp is not a
+  ; callee but an argument.
+  call void @take_longjmp(void (%struct.__jmp_buf_tag*, i32)* @longjmp)
+  ; CHECK: call void @take_longjmp(void (%struct.__jmp_buf_tag*, i32)* bitcast (void (i32, i32)* @emscripten_longjmp to void (%struct.__jmp_buf_tag*, i32)*))
+  ret void
+}
+
 declare void @foo()
 ; Function Attrs: returns_twice
 declare i32 @setjmp(%struct.__jmp_buf_tag*) #0
Index: llvm/lib/Target/WebAssembly/WebAssemblyLowerEmscriptenEHSjLj.cpp
===================================================================
--- llvm/lib/Target/WebAssembly/WebAssemblyLowerEmscriptenEHSjLj.cpp
+++ llvm/lib/Target/WebAssembly/WebAssemblyLowerEmscriptenEHSjLj.cpp
@@ -644,19 +644,29 @@
   SmallVector<CallInst *, 8> ToErase;
   LLVMContext &C = LongjmpF->getParent()->getContext();
   IRBuilder<> IRB(C);
+
+  // For calls to longjmp, replace it with emscripten_longjmp and cast its first
+  // argument (jmp_buf*) to int
   for (User *U : LongjmpF->users()) {
     auto *CI = dyn_cast<CallInst>(U);
-    if (!CI)
-      report_fatal_error("Does not support indirect calls to longjmp");
-    IRB.SetInsertPoint(CI);
-    Value *Jmpbuf =
-        IRB.CreatePtrToInt(CI->getArgOperand(0), IRB.getInt32Ty(), "jmpbuf");
-    IRB.CreateCall(EmLongjmpF, {Jmpbuf, CI->getArgOperand(1)});
-    ToErase.push_back(CI);
+    if (CI && CI->getCalledFunction() == LongjmpF) {
+      IRB.SetInsertPoint(CI);
+      Value *Jmpbuf =
+          IRB.CreatePtrToInt(CI->getArgOperand(0), IRB.getInt32Ty(), "jmpbuf");
+      IRB.CreateCall(EmLongjmpF, {Jmpbuf, CI->getArgOperand(1)});
+      ToErase.push_back(CI);
+    }
   }
-
   for (auto *I : ToErase)
     I->eraseFromParent();
+
+  // If we have any remaining uses of longjmp's function pointer, replace it
+  // with (int(*)(jmp_buf*, int))emscripten_longjmp.
+  if (!LongjmpF->uses().empty()) {
+    Value *EmLongjmp =
+        IRB.CreateBitCast(EmLongjmpF, LongjmpF->getType(), "em_longjmp");
+    LongjmpF->replaceAllUsesWith(EmLongjmp);
+  }
 }
 
 bool WebAssemblyLowerEmscriptenEHSjLj::runOnModule(Module &M) {


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