[uml-devel] Re: Bad handling of invalif systemcalls

[Jeff Dike <jdike@addtoit.com>]

bstroesser@fujitsu-siemens.com said:
> AFAICS, the only solution for this is using the PTRACE_O_TRACESYSGOOD
> option. This option seems to be specific for linux, but the problem
> maybe is specific for linux, too. 

Another solution is to read the instruction.

However TRACESYSGOOD is cleaner.  My only concern is whether that limits the
hosts that UML will run on.  If TRACESYSGOOD has been around for the 2.4
series, then that's OK.

I would be tempted to #define SIGSYSCALL (SIGTRAP + 0x80) or something just
to make the +0x80 bit less magic-looking.

> For the third patch I'm quite anxious, that there could go something
> wrong when using the debugger. I don't understand much about this.
> Maybe someone else could look into this? 

 				if(!tracing && (debugger_pid != -1)){
 					child_signal(pid, status);
 					continue;
 				}
 				tracing = 0;
				if(do_syscall(task, pid))
					sig = SIGUSR2;

OK, what this says is
	if we are running in the kernel, not userspace (!tracing)
	and we are debugging UML (debugger_pid != -1)
	then we fake the syscall-traced gdb into thinking the SIGTRAP was sent
	to the process

	Otherwise we call do_syscall, which will check the syscall number 
	and return true if it thinks it's handling a syscall.  In that case,
	we hit the process with SUGUSR2 in order to force it into the UML
	syscall handler.

So, if we get SIGTRAP + 0x80, we know we have a syscall, and the debugging
stuff can just go away.  You can look at this sort of mathematically, and
say SIGTRAP + 0x80 => tracing, so that if(!tracing...) can just be deleted.

Similarly, do_syscall will always return true, so you don't need to check its
return, which you have removed.

In the SIGTRAP case, you might as well inline do_sigtrap.  One line functions
are pretty much a waste.  In any case, I don't understand why you're doing
that.  orig_eax should already be -1.
	
				Jeff



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