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Re: ptrace for mips n32 and n64

On Fri, Mar 14, 2003 at 12:39:29PM -0300, Alexandre Oliva wrote:
> On Mar 14, 2003, Daniel Jacobowitz <drow at mvista dot com> wrote:
> > On Fri, Mar 14, 2003 at 11:35:42AM -0300, Alexandre Oliva wrote:
> >> Yay.  Lots of code duplication.  I'm sure Uli will love this patch.
> >> :-/ Ok?  (the point being that ptrace must take as argument and return
> >> 64-bit values on n32)
> > Why must it?
> Because that's the ABI defined by the kernel, as much as I dislike
> it.  Of course, glibc could adapt the interface and return longs even
> though the kernel gives it a long long, and pass a long long where it
> gets just a long.  I don't know much about the interface of ptrace,
> anyway.  I just did what Kevin told me he needed for his debugging
> code to work.

Kevin, mind enlightening me?  I don't see how this works, either in
principle or with the mips64-linux port as contributed to GDB.

> > I can't think of any reason for it to take 64-bit
> > values.  It'll also be a tremendous headache, since you'll have to cast
> > any pointers passed to ptrace.
> If you pass a pointer to ptrace, it will be sign-extended to 64 bits,
> just as it should.  No hassle.

Eh?  No it won't.  ptrace is exported as a varargs function.  Think
about what happens when you pass a 32-bit pointer to a varargs function
that pops a long long argument.  It'll die flaming death.  GDB's been
full of this kind of bug historically.

Daniel Jacobowitz
MontaVista Software                         Debian GNU/Linux Developer

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