Re: ptrace for mips n32 and n64

[Kevin Buettner <kevinb at redhat dot com>]

On Mar 14, 10:46am, Daniel Jacobowitz wrote:

> 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.

It works in RDA.  I haven't spent much time on getting a native
GDB going.  The mips64 linux specific changes that I've contributed
for GDB were largely to get core file support working.

Anyway, for n32, ptrace() needs 64 bit arguments and return values
because of the need to fetch and store 64-bit registers.  If we want
to transfer only 32-bit values, then the register numbers associated
with PTRACE_PEEKUSER / PTRACE_POKEUSER will have to change.  (Recall
that MIPS uses 0,1,2,...,31 for r0 thru r31.)

Kevin