Re: APIC, AMD-K6/2 -mcpu=586...

[Bill Pringlemeir <bpringle@sympatico.ca>]

>>>> On 05.18 Bill Pringlemeir wrote:

 >> Why don't the build scripts run a dummy file to determine where
 >> the floating point registers should be placed?
 >> 
 >> ...  const int value = offsetof(struct task_struct,
 >> thread.i387.fxsave) & 15; ...

>>>>> "JAM" == J A Magallon <jamagallon@able.es> writes:

 JAM> That is not the problem. The problem is that the registers have
 JAM> to lay in a defined way, transcribed to a C struct, and that
 JAM> pgcc lays badly that struct.

Yes, I understand that.  I was showing a way to find the value of padding
needed to align the register store in the structure.  Perhaps I should have
shown a mod to asm/processor.h,

...
        /* floating point info */
#if PAD_SIZE  /* not needed if gcc accepts zero size arrays? */
        unsigned char fpAlign[PAD_SIZE];
#endif
	union i387_union	i387;
...

Before compiling the `real source', the dummy file would be compiled
with PAD_SIZE set to zero.  Then objdump (or some other tool) can find
out what the value is.  Then when the task_struct is compiled in the
kernel, PAD_SIZE is set to the appropriate value to align the
structure.

I was describing a way to make things independent of the compiler layout
of the structs.  However, this complicates the build process, and people
might not like the padding due to cache alignment details.

I am pretty sure what I am saying works... It might not be right though.

regards,
Bill Pringlemeir.