On 04/03/2020 21:45, Jim Ingham via llvm-dev wrote: > As you have seen, different machine architectures do different things after > hitting a trap. On x86_64, the trap instruction is executed, and then you > stop, so the PC is left after the stop. On arm64, when execution halts the > pc is still pointing at the trap instruction. > > I don't think lldb should be in the business of telling systems how they > should report stops, especially since that is certainly something we can > handle in lldb. > > For traps that lldb recognizes as ones it is using for breakpoints, it > already has to handle this difference for you. But for traps we know nothing > about we don't do anything special. > > I think it would be entirely reasonable that whenever lldb encounters a trap > instruction that isn't one of ours it should always move the PC after the > trap before returning control to the user. I can't see why you would want to > keep hitting the trap over and over. I've received several bugs (on the > Apple bug reporter side) for this feature. This might be something we teach > lldb-server & debugserver to do, rather than lldb but that's an > implementation detail... > > For now, on architectures where the trap doesn't execute, you just need to > move the pc past the trap by hand (with the "thread jump" command) before > continuing. That has always been safe on arm64 so far as I can tell. > > Jim
Yes, this is something that has bugged me too. While I think it would be nice if the OSes hid these architecture quirks (hell, I think it would be nice if the CPU manufacturers made this consistent so that the OS doesn't need to hide it), I think that changing that at this point is very unlikely, and so working around it in lldb is probably the best we can do. I am not sure what is the official position on continuing from a debug trap, but I think that without that ability, the concept would be pretty useless. A quick example <https://godbolt.org/z/-8voBz> shows that clang produces the "expected" output even at -O3. In fact, on aarch64, __builtin_debugtrap() and __builtin_trap() produce the same instruction, and the only difference between them is that the latter also triggers DCE of everything coming after it. pl _______________________________________________ lldb-dev mailing list lldb-dev@lists.llvm.org https://lists.llvm.org/cgi-bin/mailman/listinfo/lldb-dev
