On Wed, 3 Feb 2021 22:17:02 GMT, Bernhard Urban-Forster <bur...@openjdk.org> wrote:
>> To answer my own question, it seems that code is still needed on `x86_64` >> for `lldb` with `EXC_MASK_BAD_ACCESS` or we keep tripping over >> `EXC_BAD_ACCESS` >> >> Remaining questions: >> >> a) why we need `EXC_MASK_ARITHMETIC` ? >> b) we hit `signal SIGSEGV` in debugger even with the code in place, any way >> to avoid that? >> c) does `BSD aarch64` need only `EXC_MASK_BAD_INSTRUCTION` or does it need >> `EXC_MASK_BAD_ACCESS` as well? >> d) can we `#ifdef` the `EXC_MASK_BAD_INSTRUCTION` part of the mask only to >> apply to `aarch64`? > > Thanks for your questions Gerard. > >> Part of the comment said This work-around is not necessary for 10.5+, as >> CrashReporter no longer intercedes on caught fatal signals. > > That comment can probably be deleted since minversion is anyway 10.9 (and > soon 10.12 https://github.com/openjdk/jdk/pull/2268 ). > >> Do you know if this also apply to lldb or is it gdb only specific? How do >> you run gdb on macOS nowadays anyhow? > > `lldb` is shipped with Xcode, `gdb` isn't. You would need to build and sign > it yourself, I haven't tried that in a while. So, we should update that > comment to talk about `lldb` 🙂 > >> a) why we need `EXC_MASK_ARITHMETIC` ? > > I _believe_ this dates back to i386. As far as I can tell this isn't needed > for x86_64 or aarch64. I guess we can remove it, the worst case is that it > makes the debugging experience of the runtime a little bit worse. OTOH it > doesn't hurt either to have it here. > >> b) we hit signal SIGSEGV in debugger even with the code in place, any way to >> avoid that? > > The equivalent for `handle SIGSEGV nostop noprint` (gdb) in lldb is `process > handle -n false -p true -s false SIGSEGV`. > >> c) does `BSD aarch6` need only `EXC_MASK_BAD_INSTRUCTION` or does it need >> `EXC_MASK_BAD_ACCESS` as well? > > aarch64 needs `EXC_MASK_BAD_ACCESS` at least for implicit null checking, > there might be other cases. > >> d) can we `#ifdef` the `EXC_MASK_BAD_INSTRUCTION` part of the mask only to >> apply to `aarch64`? > > Maybe. I don't see any value in it though, except making the code more > complicated to read 🙂 I don't like the idea of using masks on architectures that do not require them. How about something like this? `#if defined(__APPLE__)` ` // lldb (gdb) installs both standard BSD signal handlers, and mach exception` ` // handlers. By replacing the existing task exception handler, we disable lldb's mach` ` // exception handling, while leaving the standard BSD signal handlers functional.` ` //` ` // EXC_MASK_BAD_ACCESS needed by all architectures for NULL ptr checking` ` // EXC_MASK_ARITHMETIC needed by i386` ` // EXC_MASK_BAD_INSTRUCTION needed by aarch64 to initiate deoptimization` ` kern_return_t kr;` ` kr = task_set_exception_ports(mach_task_self(),` ` EXC_MASK_BAD_ACCESS` ` NOT_LP64(| EXC_MASK_ARITHMETIC)` ` AARCH64_ONLY(| EXC_MASK_BAD_INSTRUCTION),` ` MACH_PORT_NULL,` ` EXCEPTION_STATE_IDENTITY,` ` MACHINE_THREAD_STATE);` ` ` ` assert(kr == KERN_SUCCESS, "could not set mach task signal handler");` `#endif` If I just knew why i386 needs `EXC_MASK_ARITHMETIC` and add that to the comment I would be personally happy with that chunk of code. ------------- PR: https://git.openjdk.java.net/jdk/pull/2200
