lkml.org 
[lkml]   [2017]   [Oct]   [5]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
/
From
Date
SubjectRe: [PATCH] x86/alternatives: Fix alt_max_short macro to really be a max()
On 5 October 2017 at 14:52, Michael Matz <matz@suse.de> wrote:
> On Thu, 5 Oct 2017, Borislav Petkov wrote:
>> On Thu, Oct 05, 2017 at 02:35:33PM +0200, Mathias Krause wrote:
>> > Note the "<"! ...comment is wrong, though the implementation works!
>>
>> I know, I realized that when I looked at alternative-asm.h. Wanted to
>> double-check it with Micha first.
>
> Yeah, for bit-twiddling the result of arithmetic would need to be
> booleanized first, or alternatively the boolean operators be used in the
> first place. So if '<' works then that's better in this context.

Ack!

> (In a different context, or in the same one there definitely was a problem
> with using '<', but I can't remember the details, it's too long ago we
> discussed about this; maybe it even was a problem only with some binutils
> versions. So I'd suggest using the more obvious way until problems
> reoccur, and then document why exactly using relational ops was a problem
> ;-) )

Might be because the "true" value of gas' < operator is non-obvious
with being -1. But, well, if you don't know, I don't know either ;)

Anyways, the alt_max_short() macro in alternative.h is plain wrong
while the one in alternative-asm.h works and is used in a few places,
even with varying lengths of the alternatives (e.g.
arch/x86/entry/vdso/vdso32/system_call.S,
arch/x86/lib/{clear_page_64.S,memcpy_64.S,memset_64.S}), therefore
proves to be functional.


Thanks,
Mathias

\
 
 \ /
  Last update: 2017-10-05 15:02    [W:0.066 / U:0.212 seconds]
©2003-2017 Jasper Spaans. hosted at Digital OceanAdvertise on this site