[RFC,6/7] y2038: Support for Y2038 safe time on 32 bit systems (generic code)
Commit Message
* include/features.h:
Add logic to set __USE_TIME_BITS64 according to passed (when building
userspace Y2038 safe program on 32 bit system) _TIME_BITS and
_FILE_OFFSET_BITS
* manual/creature.texi: Add description of _TIME_BITS
* time/bits/types/struct_timespec.h:
Add "aliasing" (in preprocessor level) for struct timespec to struct
__timespec64 (in userspace) when running on 32 bit system with Y2038
support
* time/bits/types/time_t.h:
Use __time64_t as time_t when __USE_TIME_BITS64 is defined
---
include/features.h | 19 +++++++++++++++++++
manual/creature.texi | 28 ++++++++++++++++++++++++++++
time/bits/types/struct_timespec.h | 8 ++++++++
time/bits/types/time_t.h | 4 ++++
4 files changed, 59 insertions(+)
Comments
On Wed, 27 Mar 2019, Lukasz Majewski wrote:
> * include/features.h:
> Add logic to set __USE_TIME_BITS64 according to passed (when building
> userspace Y2038 safe program on 32 bit system) _TIME_BITS and
> _FILE_OFFSET_BITS
Nothing like this should be added until *every* public API has support for
_TIME_BITS=64 (then the support for it should be added for all APIs at
once - all the header changes and all the new symbol versions).
> +/* we need to know the word size in order to check the time size */
Comment style.
> +#if defined _TIME_BITS
> +# if _TIME_BITS == 64
> +# if ! defined(_FILE_OFFSET_BITS) || _FILE_OFFSET_BITS != 64
Space before '('
> +# error _TIME_BIT==64 is allowed only when _FILE_OFFSET_BITS==64
> +# error __TIME_BITS=32 is not compatible with __WORDSIZE > 32
It should be _TIME_BITS. Not _TIME_BIT, not __TIME_BITS. Please spell
the name consistently throughout.
@@ -365,6 +365,25 @@
# define __USE_FILE_OFFSET64 1
#endif
+/* we need to know the word size in order to check the time size */
+#include <bits/wordsize.h>
+
+#if defined _TIME_BITS
+# if _TIME_BITS == 64
+# if ! defined(_FILE_OFFSET_BITS) || _FILE_OFFSET_BITS != 64
+# error _TIME_BIT==64 is allowed only when _FILE_OFFSET_BITS==64
+# elif __WORDSIZE == 32
+# define __USE_TIME_BITS64 1
+# endif
+# elif __TIME_BITS == 32
+# if __WORDSIZE > 32
+# error __TIME_BITS=32 is not compatible with __WORDSIZE > 32
+# endif
+# else
+# error Invalid _TIME_BITS value (can only be 32 or 64)
+# endif
+#endif
+
#if defined _DEFAULT_SOURCE
# define __USE_MISC 1
#endif
@@ -165,6 +165,34 @@ This macro was introduced as part of the Large File Support extension
(LFS).
@end defvr
+@defvr Macro _TIME_BITS
+This macro determines the bit size of @code{time_t} (and therefore the
+bit size of all @code{time_t} derived types and the prototypes of all
+related functions). If @code{_TIME_BITS} is undefined, the bit size of
+time_t equals the bit size of the architecture.
+
+If @code{_TIME_BITS} is undefined, or if @code{_TIME_BITS} is defined
+to the value @code{32} and @code{__WORDSIZE} is defined to the value
+@code{32}, or or if @code{_TIME_BITS} is defined to the value @code{64}
+and @code{__WORDSIZE} is defined to the value @code{64}, nothing changes.
+
+If @code{_TIME_BITS} is defined to the value @code{64} and if
+@code{__WORDSIZE} is defined to the value @code{32}, then the @w{64 bit}
+time API and implementation are used even though the architecture word
+size is @code{32}. Also, if the kernel provides @w{64 bit} time support,
+it is used; otherwise, the @w{32 bit} kernel time support is used (with
+no provision to address kernel Y2038 shortcomings).
+
+If @code{_TIME_BITS} is defined to the value @code{32} and if
+@code{__WORDSIZE} is defined to the value @code{64}, then a compile-time
+error is emitted.
+
+If @code{_TIME_BITS} is defined to a value different from both @code{32}
+and @code{64}, then a compile-time error is emitted.
+
+This macro was introduced as part of the Y2038 support.
+@end defvr
+
@defvr Macro _ISOC99_SOURCE
@standards{GNU, (none)}
If this macro is defined, features from ISO C99 are included. Since
@@ -4,6 +4,9 @@
#include <bits/types.h>
+/* Use the original definition for 64-bit arches
+ or when 64-bit-time by default has *not* been requested */
+#if __WORDSIZE > 32 || ! defined(__USE_TIME_BITS64)
/* POSIX.1b structure for a time value. This is like a `struct timeval' but
has nanoseconds instead of microseconds. */
struct timespec
@@ -11,5 +14,10 @@ struct timespec
__time_t tv_sec; /* Seconds. */
__syscall_slong_t tv_nsec; /* Nanoseconds. */
};
+#else
+# include <bits/types/struct___timespec64.h>
+/* Use the 64-bit-time timespec by default */
+#define timespec __timespec64
+# endif
#endif
@@ -4,6 +4,10 @@
#include <bits/types.h>
/* Returned by `time'. */
+#ifdef __USE_TIME_BITS64
+typedef __time64_t time_t;
+#else
typedef __time_t time_t;
+#endif
#endif