Re: [PATCH] eal/arm: replace RTE_BUILD_BUG on non-constant

[Daniel Gregory <daniel.gregory@bytedance.com>]

On Fri, May 03, 2024 at 06:02:36PM -0700, Stephen Hemminger wrote:
> On Thu,  2 May 2024 15:21:16 +0100
> Daniel Gregory <daniel.gregory@bytedance.com> wrote:
> 
> > The ARM implementation of rte_pause uses RTE_BUILD_BUG_ON to check
> > memorder, which is not constant. This causes compile errors when it is
> > enabled with RTE_ARM_USE_WFE. eg.
> > 
> > ../lib/eal/arm/include/rte_pause_64.h: In function ‘rte_wait_until_equal_16’:
> > ../lib/eal/include/rte_common.h:530:56: error: expression in static assertion is not constant
> >   530 | #define RTE_BUILD_BUG_ON(condition) do { static_assert(!(condition), #condition); } while (0)
> >       |                                                        ^~~~~~~~~~~~
> > ../lib/eal/arm/include/rte_pause_64.h:156:9: note: in expansion of macro ‘RTE_BUILD_BUG_ON’
> >   156 |         RTE_BUILD_BUG_ON(memorder != rte_memory_order_acquire &&
> >       |         ^~~~~~~~~~~~~~~~
> > 
> > This has been the case since the switch to C11 assert (537caad2). Fix
> > the compile errors by replacing the check with an RTE_ASSERT.
> > 
> > Signed-off-by: Daniel Gregory <daniel.gregory@bytedance.com>
> 
> The only calls to rte_wait_until_equal_16 in upstream code
> are in the test_bbdev_perf.c and test_timer.c.  Looks like
> these test never got fixed to use rte_memory_order instead of __ATOMIC_ defines.

Apologies, the commit message could make it clearer, but this is also an
issue for rte_wait_until_equal_32 and rte_wait_until_equal_64.

rte_wait_until_equal_32 is used in a dozen or so lock tests with the old
__ATOMIC_ defines, as well as rte_ring_generic_pvt.h and
rte_ring_c11_pvt.h, where it's used with the new rte_memorder_order
values. Correct me if I'm wrong, but shouldn't the static assertions in
rte_stdatomic.h ensure that mixed usage doesn't cause any issues, even
if using the older __ATOMIC_ defines isn't ideal?
 
> And there should be a CI test for ARM that enables the WFE code at least
> to ensure it works!

Yes, that could've caught this sooner.