Re: [uml-devel] [Patch 1/1] uml: fix uml-use-sysemu-for-tt.patch

[Blaisorblade <blaisorblade_spam@yahoo.it>]

On Friday 12 November 2004 15:10, Bodo Stroesser wrote:
> From: Bodo Stroesser <bstroesser@fujitsu-siemens.com>
>
> The patch needs some small corrections:
> 1) local_using_sysemu must be sampled *before* the next
>     ptrace(PTRACE_SYSEMU/SYSCALL) and must stay the same until do_syscall()
>     has been done. Currently it is sampled before do_syscall() and is used
>     after this for ptrace(PTRACE_SYSEMU/SYSCALL). Even if no problem is
>     visible to the UML user, a single syscall could be executed on the host
>     when switching on sysemu. The result of this then is overwritten by the
>     syscall execution in UML.

>     Since the first event the tracer has to handle is not a syscall, it's
>     enough to initialize local_using_sysemu to 0;

Sorry, what happens if the first signal it gets is a SIGTRAP, and so 
local_using_sysemu is not yet set? If this is impossible, please add a 
comment in the code for this. However, it seems that it can get to the 
SIGTRAP case with tracing == 1. When beginning the procedure, it is 0, but it 
can be changed with the value from is_tracing(task). I've not checked if that 
is zeroed on process creation (i.e. by do_fork() calling copy_thread()), but 
just note that in the code.

> 2) Even if the host never *does* a syscall in SYSEMU, we have to write the
>     syscall number with -1, to not have the host doing syscall restarting.
>     This would happen only with an invalid syscall number equal to one of
>     the -ERESTART values.

>     But to be perfect ... 

Yes, but shouldn't this be handled on the host? Restarting a syscall which has 
never been done does not seem something that SYSEMU should allow... I don't 
want anybody to need going through the code and checking that this is safe.
-- 
Paolo Giarrusso, aka Blaisorblade
Linux registered user n. 292729


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