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MINOR: compiler: add FIXED_SIZE(size, type, name) macro

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FIXED_SIZE() macro can be used to instruct the compiler that the struct
member named <name>, handled as <type>, must be stored using <size> bytes
and that even if the type used is actualler smaller than the expected size

FIXED_SIZE_ARRAY(), similar to FIXED_SIZE() but for arrays: it takes an
extra argument which is the number of members.

They may be used for portability concerns to ensure a structure mapping
remains consistent between platforms.
This commit is contained in:
Aurelien DARRAGON 2025-10-22 19:23:02 +02:00
parent 1e4dbebef2
commit 466a603b59
1 changed files with 22 additions and 0 deletions
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22
include/haproxy/compiler.h
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@ -515,6 +515,28 @@
# define ALWAYS_PAD(x) _ALWAYS_PAD(x, __LINE__)
#endif
/* force the struct member named <name> handled as <type> to be stored using
* <size> bytes, even if the type used is actually smaller than the
* expected <size>.
*
* This can be useful to ensure struct mapping consistency between
* platforms for which native types may differ in size.
*
* /!\ you must ensure <size> cannot be smaller than actual member size
* on supported platforms, because it would result in undefined behaviors
* on such systems.
*/
#ifndef FIXED_SIZE
# define _FIXED_SIZE(size, type, name) union { char __fixed_##name[size]; type name; };
# define FIXED_SIZE(size, type, name) _FIXED_SIZE(size, type, name)
#endif
/* same as FIXED_SIZE_ARRAY but for arrays */
#ifndef FIXED_SIZE_ARRAY
# define _FIXED_SIZE_ARRAY(size, number, type, name) union { char __fixed_##name[size * number]; type name[number]; };
# define FIXED_SIZE_ARRAY(size, number, type, name) _FIXED_SIZE_ARRAY(size, number, type, name)
#endif
/* The THREAD_LOCAL type attribute defines thread-local storage and is defined
* to __thread when threads are enabled or empty when disabled.
*/