Re: [PATCH 0/24] make atomic_read() behave consistently across all architectures

Here, I should obviously admit that the semantics of *(volatile int *)& aren't any neater or well-defined in the _language standard_ at all. The

standard does say (verbatim) "precisely what constitutes as access to
object of volatile-qualified type is implementation-defined", but GCC
does help us out here by doing the right thing.

Where do you get that idea?

Try a testcase (experimentally verify).

That doesn't prove anything.  Experiments can only disprove
things.

GCC manual, section 6.1, "When
is a Volatile Object Accessed?" doesn't say anything of the
kind.

True, "implementation-defined" as per the C standard _is_ supposed to mean "unspecified behaviour where each implementation documents how the choice

is made". So ok, probably GCC isn't "documenting" this

implementation-defined behaviour which it is supposed to, but can't really

fault them much for this, probably.

GCC _is_ documenting this, namely in this section 6.1.  It doesn't
mention volatile-casted stuff.  Draw your own conclusions.


Segher

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