Workarounds for crash of clang on a-Shell

workarounds.md

The issue

When I compiled a C source code directly into a Wasm binary using clang, a-Shell crashed in a destructor of PrettyStackTraceEntry.

Specifically, the following line's assert fails after it is called some times.

https://github.com/holzschu/llvm/blob/aa7e203b38f8d2416747c28d6bd51724c0eecef6/lib/Support/PrettyStackTrace.cpp#L210

Steps to reproduce

• holzschu/llvm (aa7e203b38f8d2416747c28d6bd51724c0eecef6)
• holzschu/a-shell (dde4cfa5767b0d4813d5fc24a7006470a6917b3a)
• iPadOS 13.3
• Xcode 11.3

$ cat > test.c
int add(int a, int b) {
    return a + b;
}
$ unsetenv CCC_OVERRIDE_OPTIONS
$ clang --target=wasm32 -nostdlib -Os -s -Wl,--no-entry -Wl,--export-all -o test.wasm test.c

Then, a-Shell will crash.

Workarounds

1. Build LLVM with -DLLVM_ENABLE_BACKTRACES=OFF

   diff --git a/bootstrap.sh b/bootstrap.sh
   index 6a6d451c109..182e242bc86 100755
   --- a/bootstrap.sh
   +++ b/bootstrap.sh
   @@ -102,6 +102,7 @@ cmake -G Ninja \
    -DLLVM_ENABLE_FFI=ON \
    -DLLVM_ENABLE_THREADS=OFF \
    -DLLVM_ENABLE_TERMINFO=OFF \
   +-DLLVM_ENABLE_BACKTRACES=OFF \
    -DLIBCXX_ENABLE_EXPERIMENTAL_LIBRARY=OFF \
    -DFFI_LIBRARY_PATH=${FFI_SRCDIR}/build/Debug-iphoneos/libffi.a \
    -DFFI_INCLUDE_DIR=${FFI_SRCDIR}/build_iphoneos-arm64/include \

2. Or, remove that lines and build LLVM

   diff --git a/lib/Support/PrettyStackTrace.cpp b/lib/Support/PrettyStackTrace.cpp
   index bfb238cc853..d26f0a67c14 100644
   --- a/lib/Support/PrettyStackTrace.cpp
   +++ b/lib/Support/PrettyStackTrace.cpp
   @@ -206,6 +206,7 @@ PrettyStackTraceEntry::PrettyStackTraceEntry() {
    }
   
    PrettyStackTraceEntry::~PrettyStackTraceEntry() {
   +#if 0
    #if ENABLE_BACKTRACES
      assert(PrettyStackTraceHead == this &&
             "Pretty stack trace entry destruction is out of order");
   @@ -213,6 +214,7 @@ PrettyStackTraceEntry::~PrettyStackTraceEntry() {
      // Handle SIGINFO first, because we already started destructing.
      printForSigInfoIfNeeded();
    #endif
   +#endif
    }
   
    void PrettyStackTraceString::print(raw_ostream &OS) const { OS << Str << "\n"; }