Alfred Agrell (@Alcaro) commented about libs/unwind/src/UnwindCursor.hpp:
uint32_t lastcode = (xdata->CountOfCodes + 1) & ~1; - const uint32_t *handler = reinterpret_cast<uint32_t *>(&xdata->UnwindCodes[lastcode]); - _info.lsda = reinterpret_cast<unw_word_t>(handler+1); - if (*handler) { + // NOTE: lastcode can be equal to or greater than 2, then accessing UnwindCodes[lastcode] is + // out of bound (i.e. undefined behavior). The external memory outside the class object + // cannot be reached from a pointer to a subobject. The only valid case is when CountOfCodes + // is 0, and then lastcode will be equal 0. + // However, `reinterpret_cast` from a pointer to uint16[2] to a pointer to uint32 is not + // allowed in any case. (https://godbolt.org/z/vY1zKEvo6) + // It turns out that here we just need to check each of the array elements for zero. + const uint16_t hi = xdata->UnwindCodes[0]; + const uint16_t low = xdata->UnwindCodes[1]; +#warning "invalid reinterpret-cast" + // FIXME: Does `xdata` actually point to an array of UNWIND_INFO? + _info.lsda = reinterpret_cast<unw_word_t>(xdata+1);
AFAIK memcpy can alias anything, no need for std::byte or whatever. -- https://gitlab.winehq.org/wine/wine/-/merge_requests/10471#note_134024