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cdefs.h: Add back fallback define for __printf0like

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The format function printf0 is originally a FreeBSD extension. clang has
adopted it as an alias for printf. Starting with gcc 11, gcc doesn't do
a NULL pointer check for fmtarg. Instead, it has to be tagged with a
nonnull attribute, so this gives us the behavior we want.

For earlier gcc and other cmopilers, define it away so do not get false
positives for NULL pointers for the err*/warn* family of functions.
This also fixes -Wsystem-headers by avoiding print0 entirely. My testing
for 67d1a1cd9e didn't test that case, so I introduced a regression.

All these compilers need to be considered because __printf0like is used
in err.h and stdlib.h. Since it's used in system headers, it has to
work on all the compilers we support on FreeBSD, not just the ones that
can build FreeBSD itself.

__printf0like will likely be deleted in the future, since the proper way
to do this is with _Nullable or _Nonnull, but the compiler support for
those hasn't been completely evaluated.

Noticed by: jhb
Fixes: 67d1a1cd9e
Sponsored by: Netflix
Suggestions by: jhb
Differential Revision:	https://reviews.freebsd.org/D45836
This commit is contained in:
Warner Losh 2024-07-06 10:07:52 -06:00
parent 9a04df0515
commit 0b82dac337
1 changed files with 13 additions and 5 deletions
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18
sys/sys/cdefs.h
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@ -338,9 +338,7 @@
/*
* Compiler-dependent macros to declare that functions take printf-like
* or scanf-like arguments. They are null except for versions of gcc
* that are known to support the features properly (old versions of gcc-2
* didn't permit keeping the keywords out of the application namespace).
* or scanf-like arguments.
*/
#define __printflike(fmtarg, firstvararg) \
__attribute__((__format__ (__printf__, fmtarg, firstvararg)))
@ -352,8 +350,18 @@
#define __strftimelike(fmtarg, firstvararg) \
__attribute__((__format__ (__strftime__, fmtarg, firstvararg)))
#define __printf0like(fmtarg, firstvararg) \
__attribute__((__format__ (__printf0__, fmtarg, firstvararg)))
/*
* Like __printflike, but allows fmtarg to be NULL. FreeBSD invented 'printf0'
* for this because older versions of gcc issued warnings for NULL first args.
* Clang has always had printf and printf0 as aliases. gcc 11.0 now follows
* clang. So now this is an alias for __printflike, or nothing. In the future
* _Nullable or _Nonnull will replace this.
*/
#if defined(__clang__) || __GNUC_PREREQ__(11, 0)
#define __printf0like(fmtarg, firstvararg) __printflike(fmtarg, firstvararg)
#else
#define __printf0like(fmtarg, firstvararg)
#endif
#define __strong_reference(sym,aliassym) \
extern __typeof (sym) aliassym __attribute__ ((__alias__ (#sym)))