Re: Setting a floating point register to raw hex value

["Grzegorz Cieslewski" <cieslewski@hcs.ufl.edu>]

I have tried that solution, on the powerpc/ubuntu6.10 with gdb 6.7  and get:
(gdb) set (void*) $f0 = 0x1
Invalid cast.

I have also tried that on older x86 box with Redhat 9 with similar result
(gdb) set (void*) $R0 = 0x1
Invalid cast.


Could this some sort of platform dependent bug?

On 10/18/07, Thiago Jung Bauermann <bauerman@br.ibm.com> wrote:
> Hi,
>
> Yes, that's indeed crazy. :-)
>
> Just found out that this works:
>
> (gdb) set (void *) $f1 = 0x1
> (gdb) info reg f1
> f1             4.9406564584124654e-324  (raw 0x0000000000000001)
> --
> []'s
> Thiago Jung Bauermann
> Software Engineer
> IBM Linux Technology Center
>
>
>
> On Thu, 2007-10-18 at 15:38 -0400, Grzegorz Cieslewski wrote:
> > I have figured out a workaround but it is really ugly.
> >
> > Step 1:  Create shared object containing a union as follows
> > union longlong2double
> > {
> > long long int hexNum;
> > double floatNum;
> > } temp;
> >
> > Step 2: Force load the library at runtime into your program using
> > LD_PRELOAD environmental variable
> >
> > Step 3: When debugging the program store 0x1 into temp.hexNum;
> > (one would think that I could use the following now 'set $f0 =
> > temp.floatNum; but that yields incorrect result)
> >
> > Step4:  Overwrite the current instruction with 'load float'
> >
> > Step5: Using stepping command 'stepi 1' to write the value to the $f0
> >
> > Step6: Undo all the changes required by steps 4 and 5
> >
> > Does any one know of a simpler way because this workaround is crazy?
> >
> >
> > Greg Cieslewski
> >
> >
> >
> > On 10/12/07, Grzegorz Cieslewski <cieslewski@hcs.ufl.edu> wrote:
> > > Does any one know of a way to set a floating point register ($f0) to a
> > > arbitrary raw hex value (for example 1)
> > >
> > > I tried the following.
> > >
> > > (gdb) set $f0 = 5.0000000000000000e-324
> > > (gdb) p $f0
> > > $1 = -1.5966722476277758e+293
> > > (gdb) set $f0 = 5.0000000000000000e-324
> > >
> > > The value of 5.0000000000000000e-324 should correspond to
> > > 0x0000000000000001 in raw hex
> > >
> > > Any ideas?
> > >
> > > I am using ppc7450 (G4) if that helps.
> > >
>
>
>