[lkml]   [2019]   [Dec]   [18]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
Messages in this thread
SubjectRe: READ_ONCE() + STACKPROTECTOR_STRONG == :/ (was Re: [GIT PULL] Please pull powerpc/linux.git powerpc-5.5-2 tag (topic/kasan-bitops))
On 12.12.19 21:49, Linus Torvalds wrote:
> On Thu, Dec 12, 2019 at 11:34 AM Will Deacon <> wrote:
>> The root of my concern in all of this, and what started me looking at it in
>> the first place, is the interaction with 'typeof()'. Inheriting 'volatile'
>> for a pointer means that local variables in macros declared using typeof()
>> suddenly start generating *hideous* code, particularly when pointless stack
>> spills get stackprotector all excited.
> Yeah, removing volatile can be a bit annoying.
> For the particular case of the bitops, though, it's not an issue.
> Since you know the type there, you can just cast it.
> And if we had the rule that READ_ONCE() was an arithmetic type, you could do
> typeof(0+(*p)) __var;
> since you might as well get the integer promotion anyway (on the
> non-volatile result).
> But that doesn't work with structures or unions, of course.

We do have a READ_ONCE on the following union in s390 code.

union ipte_control {
unsigned long val;
struct {
unsigned long k : 1;
unsigned long kh : 31;
unsigned long kg : 32;

In fact this one was the original failure case why we change ACCESS_ONCE.

see arch/s390/kvm/gaccess.c

 \ /
  Last update: 2019-12-18 11:22    [W:3.895 / U:0.040 seconds]
©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site