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Warn when gettimeofday is called with non-null tzp argument.

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Since there are no known uses of gettimeofday's vestigial "get time
zone" feature that are not bugs, add a fortify-style wrapper inline to
sys/time.h that issues a warning whenever gettimeofday is called with
a second argument that is not a compile-time null pointer
constant.

At present this is only possible with GCC; clang does not implement
attribute((warning)).  The wrapper is only activated when __OPTIMIZE__
is defined because it throws false positives when optimization is off,
even though it's an always-inline function.

An oversight in the implementation of __builtin_constant_p causes it
to fail to detect compile-time *pointer* constants unless they are
cast to an integer of a different size.  (Loss of data in this cast is
harmless; the overall expression is still constant if and only if the
original pointer was.)  This is GCC bug 95514.  Thanks to
Kamil Cukrowski <kamilcukrowski@gmail.com> for the workaround.
As a precaution, I added a static assertion to debug/warning-nop.c to
make sure that the cast _is_ casting to an integer of a different
size; this is too unlikely a scenario to be worth checking in the
public header, but if someone ever adds a port where short is the
same size as intptr_t, we'll still catch it.
This commit is contained in:
Zack Weinberg 2019-08-19 13:51:25 -04:00
parent d5f4d0ac6a
commit c246b06a68
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2 changed files with 33 additions and 0 deletions
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9
debug/warning-nop.c
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@ -67,4 +67,13 @@ nop (void)
#define __builtin___strncpy_chk(dest, src, len, bos) NULL
#define __builtin_object_size(bos, level) 0
/* The code in sys/time.h that uses __warndecl has to work around GCC
bug 91554. The work-around is only effective if intptr_t is not
the same size as short. */
#include <stdint.h>
_Static_assert (sizeof (intptr_t) != sizeof (short),
"workaround for GCC bug 91554 in sys/time.h"
" is only effective when short is smaller than a pointer");
#include <string.h>
#include <sys/time.h>

24
time/sys/time.h
View File

@ -66,6 +66,30 @@ struct timezone
extern int gettimeofday (struct timeval *__restrict __tv,
void *__restrict __tz) __THROW __nonnull ((1));
#if __GNUC_PREREQ (4,3) && defined __REDIRECT && defined __OPTIMIZE__
/* Issue a warning for use of gettimeofday with a non-null __tz argument. */
__warndecl (__warn_gettimeofday_nonnull_timezone,
"gettimeofday with non-null or non-constant timezone parameter;"
" this is obsolete and inaccurate, use localtime instead");
extern int __REDIRECT_NTH (__gettimeofday_alias,
(struct timeval *__restrict __tv,
void *__restrict __tz), gettimeofday)
__nonnull ((1));
/* The double cast below works around a limitation in __builtin_constant_p
in all released versions of GCC (as of August 2019).
See <https://gcc.gnu.org/bugzilla/show_bug.cgi?id=91554>. */
__fortify_function int
__NTH (gettimeofday (struct timeval *__restrict __tv, void *__restrict __tz))
{
if (! (__builtin_constant_p ((short) (__intptr_t) __tz) && __tz == 0))
__warn_gettimeofday_nonnull_timezone ();
return __gettimeofday_alias (__tv, __tz);
}
#endif
#ifdef __USE_MISC
/* Set the current time of day and timezone information.
This call is restricted to the super-user.