On Jan 25 20:03, Jon Turney wrote: > On 25/01/2024 18:21, Corinna Vinschen wrote: > > On Jan 25 14:50, Jon Turney wrote: > > > On 24/01/2024 14:39, Corinna Vinschen wrote: > > > > On Jan 24 13:28, Jon Turney wrote: > > > > > On 23/01/2024 14:29, Corinna Vinschen wrote: > > > > > > On Jan 23 14:20, Jon Turney wrote: > [...] > > > So this situation with a JIT debugger is even stranger than my emendations > > > to the documentation say. > > > > > > Because we're hitting try_to_debug() in exception::handle(), which has > > > some > > > code to replay the exception via ExceptionContinueExecution (which I guess > > > the debugger will catch as a first-chance) (and goes into a mode where it > > > ignores the next half-million exceptions... no idea what that's about!) > > > > > > That's not the same as signal_exit() with a coredumping signal (haven't > > > checked if those are all generated from exceptions, but seems probable, so > > > the try_to_debug() there maybe isn't doing anything?), where we're going > > > to > > > exit thereafter. > > > > try_to_debug() is only calling IsDebuggerPresent() as test, and that's > > nothing but a flag in the PEB which is set by the OS after a debugger > > attached to the process. So the test is by definition extremely > > flaky, if the debugger is connecting and disconnecting, as you > > already pointed out. > > > > I'm wondering if we can't define our own way to attach to a process, > > allowing to "WaitForDebugger" as long as the debugger is a Cygwin > > debugger. If we define a matching function (along the lines of > > prctl(2) on Linux), we could change our debuggers, core dumpers > > and stracers to call this attach function. > > > > The idea would be to define some shared mutex object, the inferior > > waits for and the debugger releases after having attached. > > > > Is there really any need to support non-Cygwin debuggers? > > idk > > I think something like that used to exist a long time ago, see commit > 8abeff1ead5f3824c70111bc0ff74ff835dafa55
Yeah, just, as was the default at the time, without any trace of a *rational* why it has been removed. Also, it was too simple anyway. First, if we want to support WIndows debugger, the inferior has to check if the debugger is a Cygwin or native debugger. If a native debugger, just stick to what we have today. Otherwise: - Create a named mutex with a reproducible name (no need to use the name as parameter) and immediately grab it. - Call CreateProcess to start the debugger with CREATE_SUSPENDED flag. - Create a HANDLE array with the mutex and the process HANDLE. - Call ResumeThread on the primary debugger thread. - Call WFMO with timeout. Later on, the debugger either fails and exits or it calls ReleaseMutex after having attached to the process. - WFMO returns - If the mutex has triggered, we're being debugged (but check IsDebuggerPresent() just to be sure) - If the process has triggered, the debugger exited - If the timeout triggers... oh well. > That long predates my involvement with cygwin so I've no idea why that was > removed. It doesn't predate mine, but I know just as much as you do. Maybe the mailing list archives help, but tht's no safe bet. > > > The practical upshot of this is if the JIT debugger doesn't terminate or > > > fix > > > the erroring process, we'll just replay the faulting instruction and > > > invoke > > > the JIT debugger again. > > > > Hmm, ok. This signal stuff *is* complicated and I'd be happy > > if anybody finds out how to fix that... > > To be clear, not a problem with "core dumping signals", as the process now > always end up exiting, one way or another. > > It's only a problem when someone has set "CYGWIN=error_start:true" or > something equally dumb. Ok. Corinna
