On Fri, Jan 8, 2016 at 12:49 PM, Tony Luck [off-list ref] wrote:

Huge amounts of help from  Andy Lutomirski and Borislav Petkov to
produce this. Andy provided the inspiration to add classes to the
exception table with a clever bit-squeezing trick, Boris pointed
out how much cleaner it would all be if we just had a new field.

Linus Torvalds blessed the expansion with:
  I'd rather not be clever in order to save just a tiny amount of space
  in the exception table, which isn't really criticial for anybody.

The third field is a simple integer indexing into an array of handler
functions (I thought it couldn't be a relative pointer like the other
fields because a module may have its ex_table loaded more than 2GB away
from the handler function - but that may not be actually true. But the
integer is pretty flexible, we are only really using low two bits now).

We start out with three handlers:

0: Legacy - just jumps the to fixup IP
1: Fault - provide the trap number in %ax to the fixup code
2: Cleaned up legacy for the uaccess error hack

I think I preferred the relative function pointer approach.

Also, I think it would be nicer if the machine check code would invoke
the handler regardless of which handler (or class) is selected.  Then
the handlers that don't want to handle #MC can just reject them.

Also, can you make the handlers return bool instead of int?

--Andy

--
To unsubscribe, send a message with 'unsubscribe linux-mm' in
the body to majordomo@kvack.org.  For more info on Linux MM,
see: http://www.linux-mm.org/ .
Don't email: <a href=mailto:"dont@kvack.org"> email@kvack.org </a>