sigsuspend() and ptrace()

[Greg <gkurz@fr.ibm.com>]

Hi,

My program uses gdb to attach to a process and make it execute a specific
function thanks to the gdb 'call' command. This works quite well unless the
attached process is sleeping in sigsuspend(). I peeked into the kernel sources
and saw that the typical sigsuspend() implementation is like this :

while (1) {
	schedule();
	if (do_signal())
		return -EINTR;
}

When using ptrace attach, the target process receives a SIGSTOP but there
isn't *of course* any handler to SIGSTOP. And no way for the process to return
to userland... is it implemented that way on purpose ? How can I make suspending
processes do some *alternative* work with gdb ?

Thanks.

Greg.