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SubjectRe: READ_ONCE() + STACKPROTECTOR_STRONG == :/ (was Re: [GIT PULL] Please pull powerpc/linux.git powerpc-5.5-2 tag (topic/kasan-bitops))
On Thu, Dec 12, 2019 at 07:34:01PM +0000, Will Deacon wrote:
> void ool_store_release(volatile unsigned long *ptr, unsigned long val)
> {
> smp_store_release(ptr, val);
> }
>
> 0000000000000000 <ool_store_release>:
> 0: a9be7bfd stp x29, x30, [sp, #-32]!
> 4: 90000002 adrp x2, 0 <__stack_chk_guard>
> 8: 91000042 add x2, x2, #0x0
> c: 910003fd mov x29, sp
> 10: f9400043 ldr x3, [x2]
> 14: f9000fa3 str x3, [x29, #24]
> 18: d2800003 mov x3, #0x0 // #0
> 1c: c89ffc01 stlr x1, [x0]
> 20: f9400fa1 ldr x1, [x29, #24]
> 24: f9400040 ldr x0, [x2]
> 28: ca000020 eor x0, x1, x0
> 2c: b5000060 cbnz x0, 38 <ool_store_release+0x38>
> 30: a8c27bfd ldp x29, x30, [sp], #32
> 34: d65f03c0 ret
> 38: 94000000 bl 0 <__stack_chk_fail>
>
> It's a mess, and fixing READ_ONCE() doesn't help this case, which is why
> I was looking at getting rid of volatile where it's not strictly needed.
> I'm certainly open to other suggestions, I just haven't managed to think
> of anything else.

We could move the kernel to C++ and write:

std::remove_volatile<typeof(p)>::type __p = (p);

/me runs like hell...

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