Re: [uml-devel] Re: Again: UML on s390 (31Bit)

From: Bodo Stroesser
Date: Thu Apr 28 2005 - 10:03:59 EST

Bodo Stroesser wrote:
Martin Schwidefsky wrote:

So (!entryexit & regs->gprs[2] < 0) translates to the debugger changed the
system call to something illegal on the first of the two ptrace calls. So
patch doesn't hurt for normal, non-ptraced operation but it might hurt
users of ptrace.

I don't think, it hurts. If a debugger willingly sets the syscall number
to -1, what would happen without the patch?
The kernel will set the result -ENOSYS into grps[2]. So, even if trap
still indicates a syscall and a signal is pending, no syscall restarting
will be done.
With the patch, a debugger would observe changed behavior of the kernel
*only*, if it writes the syscall number to -1 on the first syscall
interception and then writes the result to ERESTARTXXXXX on the second,
while at the same time a signal is pending for the debugged process.

I assumed, that non of the current users of ptrace exactly does this.
If I'm wrong here, the patch *really* is bad.
To avoid any conflicts as far as possible, the -1 written and checked
as the syscall number to reset trap could be replaced by some magic
value, which then should defined in asm/ptrace.h
In terms of performance, any method, that allows to reset trap
without an additional ptrace call, is fine.

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