Re: [PATCHV5 3/3] x86, ras: Add __mcsafe_copy() function to recover from machine checks

Tony Luck
2015-12-27T06:57:29Z

On Sat, Dec 26, 2015 at 6:16 PM, Andy Lutomirski <luto@amacapital.net> wrote:
>>> We could make one of them 31-bits (since even an "allyesconfig" kernel
>>> is still much smaller than a gigabyte) to free a bit for a flag. But there
>>> are those external tools to pre-sort exception tables that would all
>>> need to be fixed too.
>
> Wait, why? The external tools sort by source address, and we'd
> squeeze the flag into the target address, no?

I was thinking that we'd need to recompute the fixup when we move
the entry to its new sorted location. So that:

ex_fixup_addr(const struct exception_table_entry *x)
{
return (unsigned long)&x->fixup + x->fixup;
}

will get the right value. Maybe this would still work out
if the fixup is a 31-bit value plus a flag, but the external
tool thinks it is a 32-bit value? I'd have to ponder that.

-Tony