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init.h: restore designated initializers in SYS_INIT_NAMED() #69411

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init.h: restore designated initializers in SYS_INIT_NAMED() #69411

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36 changes: 35 additions & 1 deletion include/zephyr/init.h
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Original file line number Diff line number Diff line change
Expand Up @@ -151,6 +151,39 @@ struct init_entry {
__attribute__((__section__( \
".z_init_" #level STRINGIFY(prio)"_" STRINGIFY(sub_prio)"_")))


/* Designated initializers where added to C in C99. There were added to
* C++ 20 years later in a much more restricted form. C99 allows many
* variations: out of order, mix of designated and not, overlap,
* override,... but C++ allows none of these. See differences detailed
* in the P0329R0.pdf C++ proposal. So use '#ifdef __cplusplus' to provide
* some separation between these two different languages and to give us
* more latitude to support more toolchains without reverting to plain
* initializers.
*/
#ifdef __cplusplus

/* When using -std=c++2a or higher, g++ (v12.2.0) reject braces for
* initializing anonymous unions because it is technically a mix of
* designated and not designated initializers which is not allowed in
* C++20. Interestingly, the _same_ g++ version does accept braces when
* using -std=c++17 or lower!
* This Zephyr test compares different -std=... values:
*
* ./scripts/twister -v -b -p qemu_cortex_a53 -T tests/lib/cpp/
*/
# define Z_INIT_SYS_INIT_DEV_NULL .dev = NULL

#else

/* While braces should be optional for anonymous unions, gcc version 4.5
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I think we're all asking what the minimum supported GCC version should be and whether that could be something that doesn't require this hack?

* (2010) and lower fail when they're missing. See example in #68118 or
* in your favorite compiler explorer.
*/
# define Z_INIT_SYS_INIT_DEV_NULL { .dev = NULL }

#endif

/** @endcond */

/**
Expand Down Expand Up @@ -205,7 +238,8 @@ struct init_entry {
#define SYS_INIT_NAMED(name, init_fn_, level, prio) \
static const Z_DECL_ALIGN(struct init_entry) \
Z_INIT_ENTRY_SECTION(level, prio, 0) __used __noasan \
Z_INIT_ENTRY_NAME(name) = {{ (init_fn_) }, { NULL } }
Z_INIT_ENTRY_NAME(name) = {.init_fn = {.sys = (init_fn_)}, \
Z_INIT_SYS_INIT_DEV_NULL}

/** @} */

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