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

[Stephen Hemminger <stephen@networkplumber.org>]

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 memory order passed to those routines must be constant.


Why not:
diff --git a/lib/eal/arm/include/rte_pause_64.h b/lib/eal/arm/include/rte_pause_64.h
index 5cb8b59056..81987de771 100644
--- a/lib/eal/arm/include/rte_pause_64.h
+++ b/lib/eal/arm/include/rte_pause_64.h
@@ -172,6 +172,8 @@ rte_wait_until_equal_32(volatile uint32_t *addr, uint32_t expected,
 {
        uint32_t value;
 
+       static_assert(__builtin_constant_p(memorder), "memory order is not a constant");
+
        RTE_BUILD_BUG_ON(memorder != rte_memory_order_acquire &&
                memorder != rte_memory_order_relaxed);
 
@@ -191,6 +193,8 @@ rte_wait_until_equal_64(volatile uint64_t *addr, uint64_t expected,
 {
        uint64_t value;
 
+       static_assert(__builtin_constant_p(memorder), "memory order is not a constant");
+
        RTE_BUILD_BUG_ON(memorder != rte_memory_order_acquire &&
                memorder != rte_memory_order_relaxed);