Messages in this thread | | | From | Denys Vlasenko <> | Date | Wed, 2 Mar 2011 16:16:50 +0100 | Subject | Re: [RFC] Proposal for ptrace improvements |
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On Wed, Mar 2, 2011 at 3:43 PM, Tejun Heo <tj@kernel.org> wrote: >> # ./a.out >> PID: 16382 >> <------ kill -STOP 16382 >> <------ kill -ABRT 16382 >> <------ kill -WINCH 16382 >> <------ kill -CONT 16382 >> sig: 28 Window changed >> sig: 18 Continued >> sig: 6 Aborted >> after sleep: errno=4 Interrupted system call >> PID: 16382 >> >> >> Therefore we also need to think about this aspect of SIGCONT behavior >> under debuggers. >> >> Do we provide for the mechanism for debuggers to >> prevent execution of *SIGCONT userspace handler*? > > Yeah, it's not different from any other signal. Just squash the > signal when ptrace signal delivery trap is taken, which is completely > separate from termination of job control stop triggered by _emission_ > of SIGCONT. The two are separate. The proposed changes don't affect > the delivery path at all. I really can't understand what your point > is. > >> And, looking at the example above, I see that on resume from stop, >> *SIGCONT userspace handler* actually doesn't run as *the first handler* >> after SIGCONT. Other pending signal's handlers may be executed before it. > > Signal delivery is not FIFO. There are some rules that the code > describes. If you're interested, take a look at the code but in > general it would be better to avoid assuming fixed order between > signal generations and deliveries.
The above example does not show any FIFO-like behavior.
What it does show is that signals queued during stop take effect immediately after job control stop is terminated.
>> How would the above example look under ptraced process? Particularly, >> this sequence: >> <------ kill -STOP 16382 >> <------ kill -ABRT 16382 >> <------ kill -WINCH 16382 >> <------ kill -CONT 16382 >> sig: 28 Window changed >> sig: 18 Continued >> sig: 6 Aborted > > There's NO difference regarding signal delivery. It stays the SAME.
Ok, let's see whether I understand you.
Assuming the program is run under simple debugger which resumes execution using PTRACE_CONT(sig) on signal delivery stops, with PTRACE_CONT(0) on ptrace stops, and doesn't do any PTRACE_CONT on job control stops, with your proposal the debugger will see and perform the following actions:
waitpid... <------ kill -STOP 16382 waitpid returns WSTOPPED, WSTOPSIG = SIGSTOP ptrace(PTRACE_GETSIGINFO) doesn't fail (=> it's signal delivery) ptrace(PTRACE_CONT, SIGSTOP) waitpid returns WSTOPPED, WSTOPSIG = SIGSTOP ptrace(PTRACE_GETSIGINFO) fails (=> it's job control stop) waitpid... <------ kill -ABRT 16382 ...debugger doesn't wake up... <------ kill -WINCH 16382 ...debugger doesn't wake up... <------ kill -CONT 16382 waitpid returns WSTOPPED, WSTOPSIG = SIGTRAP (it's a ptrace-stop) ptrace(PTRACE_CONT, 0) waitpid returns WSTOPPED, WSTOPSIG = SIGWINCH ptrace(PTRACE_CONT, SIGWINCH) waitpid returns WSTOPPED, WSTOPSIG = SIGCONT ptrace(PTRACE_CONT, SIGCONT) waitpid returns WSTOPPED, WSTOPSIG = SIGABRT ptrace(PTRACE_CONT, SIGABRT)
Correct?
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