uweigand added a comment.
In https://reviews.llvm.org/D52840#1265615, @mgorny wrote:
> The first one seems to indicate that your `libclang.so` is broken in release
> mode (optimization error?). The second one is correct (some of the tests test
> for errors, and apparently don't silence the messages).
Ok, thanks for the clarification on the second point.
As to the first issue, it turned out to be more complicated. The wrong value
results from this call in CursorVisitor::Visit
switch (Visitor(Cursor, Parent, ClientData)) {
This is a callback routine passed in from the caller, which in the case of the
Python bindings means that an FFI closure is being called.
Now, due to a historical quirk in the FFI ABI, return values of integral type
smaller than the register word size must be passed as the special "ffi_arg"
type when using FFI (either for calls or for closures). It seems the Python
2.7 code that interfaces with FFI does not correctly respect this. As a
result, it seems that when the closure returns a 32-bit value, it is not
properly extended and the high bits of the return register contain garbage.
But that violates our ABI, which requires extension to full register size.
And it seems the clang code, when built with optimization, does indeed rely on
that ABI guarantee.
So there's a bug in Python (or depending on how you want to look at it, in
libffi -- that part of the interface has also long been under-documented
unfortunately), which hits on our platform. I'll see if I can do anything
about that, but for now we'll probably want to disable those tests on SystemZ.
Repository:
rC Clang
https://reviews.llvm.org/D52840
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