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Date: Thu, 18 Oct 2007 19:38:00 -0000
From: "Grzegorz Cieslewski" <cieslewski@hcs.ufl.edu>
To: gdb@sourceware.org
Subject: Re: Setting a floating point register to raw hex value
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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.
>