search for: compiler_has_optimizer_hide_var

...barrier.h b/include/asm-generic/barrier.h > index 2cafdbb9ae4c..fa2e2ef72b68 100644 > --- a/include/asm-generic/barrier.h > +++ b/include/asm-generic/barrier.h > @@ -70,6 +70,24 @@ > #define __smp_read_barrier_depends() read_barrier_depends() > #endif > > +#if defined(COMPILER_HAS_OPTIMIZER_HIDE_VAR) && \ > + !defined(ARCH_NEEDS_READ_BARRIER_DEPENDS) > + > +#define dependent_ptr_mb(ptr, val) ({ \ > + long dependent_ptr_mb_val = (long)(val); \ > + long dependent_ptr_mb_ptr = (long)(ptr) - dependent_ptr_mb_val; \ > + \ > + BUILD_BUG_ON(sizeof(val) >...

...barrier.h b/include/asm-generic/barrier.h > index 2cafdbb9ae4c..fa2e2ef72b68 100644 > --- a/include/asm-generic/barrier.h > +++ b/include/asm-generic/barrier.h > @@ -70,6 +70,24 @@ > #define __smp_read_barrier_depends() read_barrier_depends() > #endif > > +#if defined(COMPILER_HAS_OPTIMIZER_HIDE_VAR) && \ > + !defined(ARCH_NEEDS_READ_BARRIER_DEPENDS) > + > +#define dependent_ptr_mb(ptr, val) ({ \ > + long dependent_ptr_mb_val = (long)(val); \ > + long dependent_ptr_mb_ptr = (long)(ptr) - dependent_ptr_mb_val; \ > + \ > + BUILD_BUG_ON(sizeof(val) >...

...ONFIG_SMP diff --git a/include/asm-generic/barrier.h b/include/asm-generic/barrier.h index 2cafdbb9ae4c..fa2e2ef72b68 100644 --- a/include/asm-generic/barrier.h +++ b/include/asm-generic/barrier.h @@ -70,6 +70,24 @@ #define __smp_read_barrier_depends() read_barrier_depends() #endif +#if defined(COMPILER_HAS_OPTIMIZER_HIDE_VAR) && \ + !defined(ARCH_NEEDS_READ_BARRIER_DEPENDS) + +#define dependent_ptr_mb(ptr, val) ({ \ + long dependent_ptr_mb_val = (long)(val); \ + long dependent_ptr_mb_ptr = (long)(ptr) - dependent_ptr_mb_val; \ + \ + BUILD_BUG_ON(sizeof(val) > sizeof(long)); \ + OPTIMIZER_HIDE...

So as explained in Documentation/memory-barriers.txt e.g. a load followed by a store require a full memory barrier, to avoid store being ordered before the load. Similarly load-load requires a read memory barrier. Thinking about it, we can actually create a data dependency by mixing the first loaded value into the pointer being accessed. This adds an API for this and uses it in virtio. Written

...eric/barrier.h > > index 2cafdbb9ae4c..fa2e2ef72b68 100644 > > --- a/include/asm-generic/barrier.h > > +++ b/include/asm-generic/barrier.h > > @@ -70,6 +70,24 @@ > > #define __smp_read_barrier_depends() read_barrier_depends() > > #endif > > +#if defined(COMPILER_HAS_OPTIMIZER_HIDE_VAR) && \ > > + !defined(ARCH_NEEDS_READ_BARRIER_DEPENDS) > > + > > +#define dependent_ptr_mb(ptr, val) ({ \ > > + long dependent_ptr_mb_val = (long)(val); \ > > + long dependent_ptr_mb_ptr = (long)(ptr) - dependent_ptr_mb_val; \ > > + \ > &g...