https://gcc.gnu.org/bugzilla/show_bug.cgi?id=114870
Bug ID: 114870
Summary: stddef.h problem with -Wsystem-headers on Fedora 40
Product: gcc
Version: 14.0
Status: UNCONFIRMED
Severity: normal
Priority: P3
Component: c
Assignee: unassigned at gcc dot gnu.org
Reporter: eggert at cs dot ucla.edu
Target Milestone: ---
Created attachment 58049
--> https://gcc.gnu.org/bugzilla/attachment.cgi?id=58049&action=edit
fix stddef.h to survive multiple includes, some with __need_size_t etc.
I found this when trying to build GNU diffutils on Fedora 40. This is gcc (GCC)
14.0.1 20240411 (Red Hat 14.0.1-0) on x86-64. Compile the following two-line
program t.c with 'gcc -std=gnu23 -Wsystem-headers -E t.c >t.i':
#include <stddef.h>
#include <time.h>
GCC issues the following diagnostics:
In file included from /usr/include/time.h:29,
from t.c:2:
/usr/lib/gcc/x86_64-redhat-linux/14/include/stddef.h:457:9: warning:
"__STDC_VERSION_STDDEF_H__" redefined
457 | #define __STDC_VERSION_STDDEF_H__ 202311L
| ^~~~~~~~~~~~~~~~~~~~~~~~~
In file included from t.c:1:
/usr/lib/gcc/x86_64-redhat-linux/14/include/stddef.h:457:9: note: this is the
location of the previous definition
457 | #define __STDC_VERSION_STDDEF_H__ 202311L
| ^~~~~~~~~~~~~~~~~~~~~~~~~
It seems that <stddef.h> is not properly protected against multiple includes,
some with __need_size_t and __need_NULL and some without.
The attached patch to stddef.h worked around the problem for me.
