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SubjectRe: [alpha] cleanup opDEC workaround
On Tue, Nov 20, 2001 at 10:47:48AM -0800, Richard Henderson wrote:
> In the working case, we'll enter entIF with pc==cmpteq. Add 8 gives
> stt, subtract 4 gives addt, which is engineered to be a noop.

Argh. I was thinking too much about dummy_emul case and missed the fact
that instruction at pc-4 is actually executed in alpha_fp_emul()...

> Hmm. If fp emulation isn't compiled in, we shouldn't bother
> testing this, I think. Means you can't debug fp emulation via
> modules on Multia, but I'm pretty sure I don't care.

Yes, making opDEC_check stuff `#ifdef CONFIG_MATHEMU' would be
reasonable.

> I suppose the other alternative to get the testing code out of
> the normal entIF is to create a custom entIF that is installed
> only during opDEC testing. Seems too much work...

Agreed. Alternatively, it's possible to hack dummy_emul(), which
doesn't affect the normal case.

static long dummy_emul(unsigned long pc)
{
if (opDEC_fix != 8)
return 0;
/* Trap in opDEC_check() */
if (*(u32 *)pc == 0x5bff141f) /* addt $f31, $f31, $f31 */
return 1; /* SRM updates PC correctly */
/* Broken SRM. "Emulate" cmpteq in opDEC_check() */
__asm__ __volatile__("cmpteq $f31, $f31, $f0\n");
return 1;
}
Ivan.
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