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

[Stephen Hemminger <stephen@networkplumber.org>]

On Thu, 2 May 2024 18:44:20 +0100
Daniel Gregory <daniel.gregory@bytedance.com> wrote:

> What toolchain are you using? With your change I still get errors about
> the expression not being constant:
> 
> In file included from ../lib/eal/arm/include/rte_pause.h:13,
>                  from ../lib/eal/include/generic/rte_spinlock.h:25,
>                  from ../lib/eal/arm/include/rte_spinlock.h:17,
>                  from ../lib/telemetry/telemetry.c:20:
> ../lib/eal/arm/include/rte_pause_64.h: In function ‘rte_wait_until_equal_16’:
> ../lib/eal/arm/include/rte_pause_64.h:156:23: error: expression in static assertion is not constant
> 156 |           static_assert(__builtin_constant_p(memorder), "memory order is not a constant");
>     |                         ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
> 
> I'm cross-compiling with GCC v12.2 using the
> config/arm/arm64_armv8_linux_gcc cross-file, and enabling
> RTE_ARM_USE_WFE by uncommenting it in config/arm/meson.build and setting
> its value to true.


The problem with your patch is that checking at runtime generates additional
instructions in the critical path. Looks like more of a compiler bug.