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

[Bodo Stroesser <bstroesser@fujitsu-siemens.com>]

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

	Bodo


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