Re: [Qemu-devel] [PATCH v2] linux-user: Simplify timerid checks on g_posix_timers range

[Peter Maydell]

On 22 August 2014 14:27, Andreas Färber <address@hidden> wrote:
> Am 22.08.2014 14:09, schrieb Laurent Vivier:
>> as in the kernel timer_t is an "int" (as said PMM), you should cast to
>> "int" to remove garbage on 64bit hosts and check sign ...
>
> So maybe that's the bug Alex was trying to fix downstream with the use
> of unsigned types?

I imagine the reason the SuSE tree switches to abi_ulong
for the arg* is that it fixes a bunch of bugs we have where we're
incorrectly casting a (probably 32 bit) abi_long to a 64 bit signed
host type and getting a sign-extension, when the semantics of
those particular syscalls require unsigned values. But conversely
the change probably means that places which wanted the
sign-extension are no longer getting it.

If we were writing this code from scratch then there's probably
a good argument for making the arg* be the unsigned type
rather than signed. Unfortunately at this point it's basically
impossible to change over, because we'd have to audit every
use of them in a 10,000 line file to determine whether we needed
to put a cast back in to get sign extension or not. I'd rather we
just fixed the places that don't want sign-extension, because
presumably we at least have examples of failing guest programs
we can use to tell us what the problematic syscalls are...

-- PMM