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Question on signal handling, interrupt handling

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Signal is executed in user mode, but with a different user context, then return to kernel, which return to user_mode with ret_from_syscall. The behaviour of system call when signal handler are installed with SA_RESTART depends on the system call.

A description of which system call are restarted is available in recent version of the signal overview manpage :

man 7 signal

If the SA_RESTART flag is not used, system call is not restarted.

shodanex 2010-09-03 14:05:51

Now i got what you mean by signal is executed in user mode with a different user context. In case of process receives a signal, process switches to kernel mode to handle the exception where in bitmask of the signal array of the current process is set. Right before returning to user mode, kernel checks the signal pending and calls the do_signal function to handle the signal which in turn calls handle_signal which copies the kernel hardware context, and modifies the user mode stack by invoking setup_frame.

Ganesh Kundapur 2010-09-21 19:50:19

The new stack frame contains signum, PC value pointing to user mode signal handler, return address field containing the address of the system call sigreturn. On process returning to user mode, it starts executing the signal handler and on termination executes sigreturn which makes process to switch to kernel mode where in hardware context from the user mode stack is copied back to kernel stack by restore_sigcontext(restoring the user mode stack to original state). When the sigreturn system call terminates process switches back to user mode and continue from where it is left before the signal.

Ganesh Kundapur 2010-09-21 19:54:48

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Question on signal handling, interrupt handling

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