This is the mail archive of the
libc-alpha@sourceware.org
mailing list for the glibc project.
[PATCH v2 09/10] Warn when gettimeofday is called with non-null tzp argument.
- From: Zack Weinberg <zackw at panix dot com>
- To: libc-alpha at sourceware dot org
- Cc: Joseph Myers <joseph at codesourcery dot com>, Florian Weimer <fweimer at redhat dot com>, Lukasz Majewski <lukma at denx dot de>, Alistair Francis <alistair23 at gmail dot com>, Stepan Golosunov <stepan at golosunov dot pp dot ru>, Arnd Bergmann <arnd at arndb dot de>, Adhemerval Zanella <adhemerval dot zanella at linaro dot org>, Samuel Thibault <samuel dot thibault at ens-lyon dot org>
- Date: Wed, 28 Aug 2019 11:32:35 -0400
- Subject: [PATCH v2 09/10] Warn when gettimeofday is called with non-null tzp argument.
- References: <20190828153236.18229-1-zackw@panix.com>
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.
Also make the public prototype of gettimeofday declare its second
argument with type "void *" unconditionally, consistent with POSIX.
* time/sys/time.h (__timezone_ptr_t): Delete.
(gettimeofday): Always declare second argument with type "void *".
When possible, wrap with a fortify-style inline function that
detects non-null or non-constant second argument and issues a
warning. Improve commentary.
(settimeofday): Improve commentary.
* time/gettimeofday.c (gettimeofday): Declare second argument with
type "void *".
* debug/warning-nop.c: Include sys/time.h and stdint.h.
Add static_assert to verify the requirements of the workaround
for GCC bug 95514.
---
debug/warning-nop.c | 9 +++++++++
time/gettimeofday.c | 4 ++--
time/sys/time.h | 47 ++++++++++++++++++++++++++++++++++-----------
3 files changed, 47 insertions(+), 13 deletions(-)
diff --git a/debug/warning-nop.c b/debug/warning-nop.c
index 8eeea396c3..3eab53b78f 100644
--- a/debug/warning-nop.c
+++ b/debug/warning-nop.c
@@ -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>
diff --git a/time/gettimeofday.c b/time/gettimeofday.c
index c4f642631f..5bc91fc214 100644
--- a/time/gettimeofday.c
+++ b/time/gettimeofday.c
@@ -23,10 +23,10 @@
If *TZ is not NULL, clear it.
Returns 0 on success, -1 on errors. */
int
-___gettimeofday (struct timeval *tv, struct timezone *tz)
+___gettimeofday (struct timeval *restrict tv, void *restrict tz)
{
if (__glibc_unlikely (tz != 0))
- memset (tz, 0, sizeof *tz);
+ memset (tz, 0, sizeof (struct timezone));
struct timespec ts;
if (__clock_gettime (CLOCK_REALTIME, &ts))
diff --git a/time/sys/time.h b/time/sys/time.h
index 5dbc7fc627..a4e7fd20d1 100644
--- a/time/sys/time.h
+++ b/time/sys/time.h
@@ -54,23 +54,48 @@ struct timezone
int tz_minuteswest; /* Minutes west of GMT. */
int tz_dsttime; /* Nonzero if DST is ever in effect. */
};
-
-typedef struct timezone *__restrict __timezone_ptr_t;
-#else
-typedef void *__restrict __timezone_ptr_t;
#endif
-/* Get the current time of day and timezone information,
- putting it into *TV and *TZ. If TZ is NULL, *TZ is not filled.
- Returns 0 on success, -1 on errors.
- NOTE: This form of timezone information is obsolete.
- Use the functions and variables declared in <time.h> instead. */
+/* Get the current time of day, putting it into *TV.
+ If TZ is not null, *TZ must be a struct timezone, and both fields
+ will be set to zero.
+ Calling this function with a non-null TZ is obsolete;
+ use localtime etc. instead.
+ This function itself is semi-obsolete;
+ most callers should use time or clock_gettime instead. */
extern int gettimeofday (struct timeval *__restrict __tv,
- __timezone_ptr_t __tz) __THROW __nonnull ((1));
+ 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. */
+ This call is restricted to the super-user.
+ Setting the timezone in this way is obsolete, but we don't yet
+ warn about it because it still has some uses for which there is
+ no alternative. */
extern int settimeofday (const struct timeval *__tv,
const struct timezone *__tz)
__THROW;
--
2.23.0