Hi Pedro,
I'm going to reply to both your emails here.
On Sat, Jun 02, 2007 at 08:20:12PM +0100, Pedro Alves wrote:
> Hi Kevin,
>
> glad to see you're still around :)
Heh, my silence was just because everything has been working really
well. :-)
On Sun, Jun 03, 2007 at 07:01:35PM +0100, Pedro Alves wrote:
> Danny Backx wrote:
> > I'm not sure we're talking about the same things here.
> >
>
> Yes, we are. Kevin wants __try/__except, which is syntax sugar on
> top of SEH. Start here for info on SEH on ARM WinCE:
To be clear, I'm not too concerned about using SEH or some other
mechanism. My goal is just to be able to prevent some access errors
from terminating the program.
[...]
> The exception c++ model that both mingw32ce and cegcc use is the sjlj model.
> It is similar with the SEH model on x86. It certainly works.
>
> SEH is an OS thing, so it always works, but it happens that registering
> handlers manually is much harder on ARM than it is on x86/9x/NT.
So, is it possible to have mingw32ce install a global SEH handler that
just translates the exception into an sjlj one? That is, can we
modify the standard crt0.S file so that it causes wince exceptions to
raise C++ exceptions that g++ can then handle?
[...]
> SEH is used internally by the OS dlls. For example, the IsBadWritePtr
> function
> I was suggesting to Kevin, internally does something like:
[...]
> So Kevin's code could be rewritten as something like:
>
> while (wcount--)
> {
> if (IsBadWritePtr (vaddr, sizeof (*vaddr)))
> {
> Complain (C_ERROR ("EXCEPTION while writing %08x to"
> "address %08x"),
> value, vaddr);
> }
> else
> {
> *vaddr = value;
> }
> ++vaddr;
> }
In the original haret code, there were two uses for the __try/__except
stuff: to catch invalid memory reads/writes, and to catch invalid
instructions. The memory accesses are the most common thing that
users bump into.
However, I'm a bit concerned with using IsBad{Read,Write}Ptr. It's
not clear to me from the docs that the wince code for this really
tests whether or not the access will succeed - it may be trying to
verify that the pointer is in a valid looking address range. One of
the things Haret needs to be able to do is to access obscure areas of
memory (directly accessing hardware registers, wince internals, and
other apps). I really want to try the access and then handle the
fault if one occurs. If I ask wince if the pointer is valid, it may
come back and say "no - that pointer is not in your address space",
but that may be just what the user wants to do!
Cheers,
-Kevin
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