[Lldb-commits] [lldb] [lldb][test] Skip libc++ tests if it is linked statically (PR #113935)

[Michael Buch via lldb-commits]

Michael137 wrote:

> > Agree with Pavel.
> 
> I'm not sure you do :P
> 
> > > When libcxx is linked with a program as an archive of static libraries,
> > > functions that aren't used in the program are omitted.
> > 
> > 
> > This really isn't the problem. The tests _want_ those symbols to not be present and make sure that we can find those in the `std` Clang module. So I'm pretty sure the issue isn't about what symbols get stripped from the library
> 
> There are different kinds of symbols going around here. The symbol you don't want to be in the binary is `std::vector<T>::at()` (because it can be generated from the c++ module and stuff). However, the implementation of `at()` will call (on the failure path) __libcxx_throw_out_of_range (or something, I forgot it's name), which is a non-template function defined only in some libc++ source (not header) file. The libc++ module will not contain a definition of that. And if the program never calls it, the symbol won't be extracted from the archive. I think the fix is to make sure this function is present (by depending on it in some way), without pulling in std::vector and friends.

Ah I see, thanks for elaborating! Yea that makes sense. Referencing `__throw_out_of_range` somehow might work. Or just change the function we're calling from `at` to something that doesn't pull in the symbol from the dylib? That should still provide us with coverage of calling functions from the `std` module

https://github.com/llvm/llvm-project/pull/113935