Commit f6f52f3e authored by Jim Meyering's avatar Jim Meyering Committed by facebook-github-bot-4

folly/detail/ThreadLocalDetail.h: avoid UBSAN-detected memcpy abuse

Summary: [technically, the existing code is probably a no-op on
all systems we care about, but since it is officially UB, switching
to a more strict platform could cause trouble, so it's worth fixing]

Calling memcpy with "nullptr" as 2nd argument is undefined, even when
the third argument is zero, and causes a failure when testing with an
UBSAN-enabled binary (-fsanitize=undefined).
Before this change, the buck-run test below would evoke this failure:

  [ RUN      ] ThreadLocalPtr.BasicDestructor
  folly/detail/ThreadLocalDetail.h:533:29: runtime error: null pointer passed as argument 2, which is declared to never be null
  third-party-buck/build/glibc/include/string.h:47:45: note: nonnull attribute specified here

Ironically, the failure of the target-determinator-buck_push_blocking test (due to an unrelated proxygen dep problem) would block me from landing this, so I am adding this line to override it.

Reviewed By: luciang, alexshap

Differential Revision: D2692625

fb-gh-sync-id: 8bdc5cd2899705f39c9565d640921de1f363807d
parent ffe26edc
......@@ -530,10 +530,11 @@ struct StaticMeta {
* destructing a ThreadLocal and writing to the elements vector
* of this thread.
*/
memcpy(reallocated, threadEntry->elements,
sizeof(ElementWrapper) * prevCapacity);
using std::swap;
swap(reallocated, threadEntry->elements);
if (prevCapacity != 0) {
memcpy(reallocated, threadEntry->elements,
sizeof(*reallocated) * prevCapacity);
}
std::swap(reallocated, threadEntry->elements);
}
threadEntry->elementsCapacity = newCapacity;
}
......
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