On macOS the host keeps libc++abi: libc++ binds __cxa_throw two-level,
so moving only the personality into this runtime would leave the two
halves disagreeing on the exception header. The host personalities stay
libc++abi's and libunwind's, and libc.prx serves guest code:
- the guest's libstdc++ std::exception_ptr is modelled directly, since
libc++'s differs, and the Itanium type_info layouts that libc++abi
keeps private are declared for the runtime;
- guest frames are found through their PT_GNU_EH_FRAME, using a
dl_iterate_phdr emulation over the ELF program headers that relinked
images keep in __APS5DATA,__meta (written by relinker --macos, which
comes in a later pull request);
- host frames are found by scanning __TEXT,__eh_frame;
- sceKernelGetModuleInfoForUnwind uses the same emulation and falls back
to dladdr for host images.
The libc++ paths compile only with libc++/libc++abi and the rest only
on __APPLE__, so Linux and Windows builds are unchanged.
exception_c_cleanup throws from host code, which this runtime does not
serve on macOS, so it is not built there.
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