[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index]

Re: [Xen-devel] [PATCH 5/7] x86/alt: Support for automatic padding calculations

On Mon, Feb 12, 2018 at 11:23:05AM +0000, Andrew Cooper wrote:
>  .macro ALTERNATIVE oldinstr, newinstr, feature
>  .L\@_orig_s:
>      \oldinstr
>  .L\@_orig_e:
> +     .skip (-((repl_len(1) - orig_len) > 0) * (repl_len(1) - orig_len)), 0x90

clang chokes on this expression, because of the negation at the
beginning and I'm also failing to see why are you adding such
negation. AFAICT using:

.skip (((repl_len(1) - orig_len) > 0) * (repl_len(1) - orig_len)), 0x90

Is correct: it adds the right padding if the alternative code is
bigger than the original one, while not adding anything is the
original code is greater than the alternative one.

The negation just turns the 1 to -1, thus converting the result of the
whole expression into a negative value.


Xen-devel mailing list



Lists.xenproject.org is hosted with RackSpace, monitoring our
servers 24x7x365 and backed by RackSpace's Fanatical Support®.