[Support] Use malloc instead of non-throwing new

[AaronBallman]

When allocating a memory buffer, we use a non-throwing new so that we can explicitly handle memory buffers that are too large to fit into memory. However, when exceptions are disabled, LLVM installs a custom new handler
(

llvm-project/llvm/lib/Support/InitLLVM.cpp

Line 61 in 90109d4

install_out_of_memory_new_handler();

) that explicitly crashes when we run out of memory
(

llvm-project/llvm/lib/Support/ErrorHandling.cpp

Line 188 in de14b74

static void out_of_memory_new_handler() {

) and that means this particular out-of-memory situation cannot be gracefully handled.

This was discovered while working on #embed
(#68620) on Windows and resulted in a crash rather than the preprocessor issuing a diagnostic as expected.

This patch switches away from the non-throwing new to a call to malloc (and free), which will return a null pointer without calling a custom new handler. It is the only instance in Clang or LLVM that I could find which used a non-throwing new, so I did not think we would need anything more involved than this change.

Testing this would be highly platform dependent and so it does not come with test coverage. And because it doesn't change behavior that users are likely to be able to observe, it does not come with a release note.

[llvmbot]

@llvm/pr-subscribers-llvm-support

Author: Aaron Ballman (AaronBallman)

Changes

When allocating a memory buffer, we use a non-throwing new so that we can explicitly handle memory buffers that are too large to fit into memory. However, when exceptions are disabled, LLVM installs a custom new handler
(

llvm-project/llvm/lib/Support/InitLLVM.cpp

Line 61 in 90109d4

install_out_of_memory_new_handler();

) that explicitly crashes when we run out of memory
(

llvm-project/llvm/lib/Support/ErrorHandling.cpp

Line 188 in de14b74

static void out_of_memory_new_handler() {

) and that means this particular out-of-memory situation cannot be gracefully handled.

This was discovered while working on #embed
(#68620) on Windows and resulted in a crash rather than the preprocessor issuing a diagnostic as expected.

This patch switches away from the non-throwing new to a call to malloc (and free), which will return a null pointer without calling a custom new handler. It is the only instance in Clang or LLVM that I could find which used a non-throwing new, so I did not think we would need anything more involved than this change.

Testing this would be highly platform dependent and so it does not come with test coverage. And because it doesn't change behavior that users are likely to be able to observe, it does not come with a release note.

---

Full diff: https://github.com/llvm/llvm-project/pull/92157.diff

1 Files Affected:

• (modified) llvm/lib/Support/MemoryBuffer.cpp (+2-2)

diff --git a/llvm/lib/Support/MemoryBuffer.cpp b/llvm/lib/Support/MemoryBuffer.cpp
index 4cc4fe019b75b..e30c3acdb8814 100644
--- a/llvm/lib/Support/MemoryBuffer.cpp
+++ b/llvm/lib/Support/MemoryBuffer.cpp
@@ -98,7 +98,7 @@ class MemoryBufferMem : public MB {
 
   /// Disable sized deallocation for MemoryBufferMem, because it has
   /// tail-allocated data.
-  void operator delete(void *p) { ::operator delete(p); }
+  void operator delete(void *p) { std::free(p); }
 
   StringRef getBufferIdentifier() const override {
     // The name is stored after the class itself.
@@ -315,7 +315,7 @@ WritableMemoryBuffer::getNewUninitMemBuffer(size_t Size,
   size_t RealLen = StringLen + Size + 1 + BufAlign.value();
   if (RealLen <= Size) // Check for rollover.
     return nullptr;
-  char *Mem = static_cast<char*>(operator new(RealLen, std::nothrow));
+  char *Mem = static_cast<char*>(std::malloc(RealLen));
   if (!Mem)
     return nullptr;
 

[github-actions]

✅ With the latest revision this PR passed the C/C++ code formatter.

[cor3ntin]

I think we want a comment in the code, it's pretty subtle. otherwise LGTM

[jyknight]

Ugh, that's an annoying misuse of the new handler. :(

But if this is the only place it affects, this workaround SGTM (with added comment as mentioned).