Re: [PATCH 2/2] ARM: domains: add memory dependencies to get_domain/set_domain

Robert Jarzmik
2015-09-11T15:01:27Z

Russell King <rmk+kernel@arm.linux.org.uk> writes:

> We need to have memory dependencies on get_domain/set_domain to avoid
> the compiler over-optimising these inline assembly instructions.
>
> Loads/stores must not be reordered across a set_domain(), so introduce
> a compiler barrier for that assembly.
>
> The value of get_domain() must not be cached across a set_domain(), but
> we still want to allow the compiler to optimise it away. Introduce a
> dependency on current_thread_info()->cpu_domain to avoid this; the new
> memory clobber in set_domain() should therefore cause the compiler to
> re-load this. The other advantage of using this is we should have its
> address in the register set already, or very soon after at most call
> sites.
>
> Signed-off-by: Russell King <rmk+kernel@arm.linux.org.uk>
Tested-by: Robert Jarzmik <robert.jarzmik@free.fr>

The test is failing without these 2 patches, while with them, an unaligned
access is fixed, and the generated code looks good :
7ac: ee13cf10 mrc 15, 0, ip, cr3, cr0, {0}
7b0: e3cc300c bic r3, ip, #12
7b4: e58dc014 str ip, [sp, #20]
7b8: e3833004 orr r3, r3, #4
7bc: ee033f10 mcr 15, 0, r3, cr3, cr0, {0}

Cheers.

--
Robert