[llvm] 7e6793a - [WebAssembly] Generate unreachable after __stack_chk_fail

[Heejin Ahn via llvm-commits]

Author: Heejin Ahn
Date: 2020-07-08T01:02:05-07:00
New Revision: 7e6793aa33dd61ed9dd531871fce30c1b7978e13

URL: https://github.com/llvm/llvm-project/commit/7e6793aa33dd61ed9dd531871fce30c1b7978e13
DIFF: https://github.com/llvm/llvm-project/commit/7e6793aa33dd61ed9dd531871fce30c1b7978e13.diff

LOG: [WebAssembly] Generate unreachable after __stack_chk_fail

`__stack_chk_fail` does not return, but `unreachable` was not generated
following `call __stack_chk_fail`. This had a possibility to generate an
invalid binary for functions with a return type, because
`__stack_chk_fail`'s return type is void and `call __stack_chk_fail` can
be the last instruction in the function whose return type is non-void.
Generating `unreachable` after it makes sure CFGStackify's
`fixEndsAtEndOfFunction` handles it correctly.

Reviewed By: tlively

Differential Revision: https://reviews.llvm.org/D83277

Added: 
    

Modified: 
    llvm/lib/CodeGen/SelectionDAG/SelectionDAGBuilder.cpp
    llvm/test/CodeGen/WebAssembly/stack-protector.ll

Removed: 
    


################################################################################
diff  --git a/llvm/lib/CodeGen/SelectionDAG/SelectionDAGBuilder.cpp b/llvm/lib/CodeGen/SelectionDAG/SelectionDAGBuilder.cpp
index 05813296997e..f5e12101c8e9 100644
--- a/llvm/lib/CodeGen/SelectionDAG/SelectionDAGBuilder.cpp
+++ b/llvm/lib/CodeGen/SelectionDAG/SelectionDAGBuilder.cpp
@@ -2668,6 +2668,11 @@ SelectionDAGBuilder::visitSPDescriptorFailure(StackProtectorDescriptor &SPD) {
   // Passing 'true' for doesNotReturn above won't generate the trap for us.
   if (TM.getTargetTriple().isPS4CPU())
     Chain = DAG.getNode(ISD::TRAP, getCurSDLoc(), MVT::Other, Chain);
+  // WebAssembly needs an unreachable instruction after a non-returning call,
+  // because the function return type can be 
diff erent from __stack_chk_fail's
+  // return type (void).
+  if (TM.getTargetTriple().isWasm())
+    Chain = DAG.getNode(ISD::TRAP, getCurSDLoc(), MVT::Other, Chain);
 
   DAG.setRoot(Chain);
 }

diff  --git a/llvm/test/CodeGen/WebAssembly/stack-protector.ll b/llvm/test/CodeGen/WebAssembly/stack-protector.ll
index 2b6521b43770..eda24bcb366b 100644
--- a/llvm/test/CodeGen/WebAssembly/stack-protector.ll
+++ b/llvm/test/CodeGen/WebAssembly/stack-protector.ll
@@ -1,13 +1,13 @@
 ; RUN: llc -verify-machineinstrs -mtriple=wasm32-unknown-unknown < %s | FileCheck -check-prefix=WASM32 %s
 
-; WASM32: i32.load        28
-; WASM32-NEXT: i32.ne
-; WASM32-NEXT: br_if           0
-
-; WASM32: __stack_chk_fail
-
 @"\01LC" = internal constant [11 x i8] c"buf == %s\0A\00"		; <[11 x i8]*> [#uses=1]
 
+; WASM32-LABEL: test
+; WASM32:      i32.load        28
+; WASM32:      br_if           0
+; WASM32:      call __stack_chk_fail
+; WASM32-NEXT: unreachable
+
 define void @test(i8* %a) nounwind ssp {
 entry:
 	%a_addr = alloca i8*		; <i8**> [#uses=2]
@@ -25,6 +25,27 @@ return:		; preds = %entry
 	ret void
 }
 
+; WASM32-LABEL: test_return_i32
+; WASM32:      call __stack_chk_fail
+; WASM32-NEXT: unreachable
+
+define i32 @test_return_i32(i8* %a) nounwind ssp {
+entry:
+  %a_addr = alloca i8*    ; <i8**> [#uses=2]
+  %buf = alloca [8 x i8]    ; <[8 x i8]*> [#uses=2]
+  %"alloca point" = bitcast i32 0 to i32    ; <i32> [#uses=0]
+  store i8* %a, i8** %a_addr
+  %buf1 = bitcast [8 x i8]* %buf to i8*    ; <i8*> [#uses=1]
+  %0 = load i8*, i8** %a_addr, align 4    ; <i8*> [#uses=1]
+  %1 = call i8* @strcpy(i8* %buf1, i8* %0) nounwind    ; <i8*> [#uses=0]
+  %buf2 = bitcast [8 x i8]* %buf to i8*    ; <i8*> [#uses=1]
+  %2 = call i32 (i8*, ...) @printf(i8* getelementptr ([11 x i8], [11 x i8]* @"\01LC", i32 0, i32 0), i8* %buf2) nounwind    ; <i32> [#uses=0]
+  br label %return
+
+return:    ; preds = %entry
+  ret i32 0
+}
+
 declare i8* @strcpy(i8*, i8*) nounwind
 
 declare i32 @printf(i8*, ...) nounwind