* [RFC] y2038: test: Add _Static_assert() check when __USE_TIME_BITS64 is defined
@ 2020-12-09 14:53 Lukasz Majewski
2020-12-10 0:42 ` Paul Eggert
0 siblings, 1 reply; 4+ messages in thread
From: Lukasz Majewski @ 2020-12-09 14:53 UTC (permalink / raw)
To: Joseph Myers, Paul Eggert, Adhemerval Zanella
Cc: Alistair Francis, Arnd Bergmann, Alistair Francis, GNU C Library,
Florian Weimer, Carlos O'Donell, Stepan Golosunov,
Andreas Schwab, Zack Weinberg, Siddhesh Poyarekar,
Lukasz Majewski
This check is added to exported time/time.h file to check in the compile
time if time_t and struct timespec have proper sizes and alignment.
It shall prevent from compiling user programs with -D_TIME_BITS=64 when
time related data structures are not supporting 64 bit time.
---
time/time.h | 8 ++++++++
1 file changed, 8 insertions(+)
diff --git a/time/time.h b/time/time.h
index 9a74f01b2f..d293ff3dc5 100644
--- a/time/time.h
+++ b/time/time.h
@@ -446,4 +446,12 @@ extern int getdate_r (const char *__restrict __string,
__END_DECLS
+#define CHECK_TIME64_SIZE(__name, __len) \
+ _Static_assert (sizeof (__name) == __len, "Size of " #__name " != " #__len)
+
+#ifdef __USE_TIME_BITS64
+ CHECK_TIME64_SIZE(time_t, 8);
+ CHECK_TIME64_SIZE(struct timespec, 16);
+#endif
+
#endif /* time.h. */
--
2.20.1
^ permalink raw reply [flat|nested] 4+ messages in thread
* Re: [RFC] y2038: test: Add _Static_assert() check when __USE_TIME_BITS64 is defined
2020-12-09 14:53 [RFC] y2038: test: Add _Static_assert() check when __USE_TIME_BITS64 is defined Lukasz Majewski
@ 2020-12-10 0:42 ` Paul Eggert
2020-12-13 11:48 ` Lukasz Majewski
0 siblings, 1 reply; 4+ messages in thread
From: Paul Eggert @ 2020-12-10 0:42 UTC (permalink / raw)
To: Lukasz Majewski, Joseph Myers, Adhemerval Zanella
Cc: Alistair Francis, Arnd Bergmann, Alistair Francis, GNU C Library,
Florian Weimer, Carlos O'Donell, Stepan Golosunov,
Andreas Schwab, Zack Weinberg, Siddhesh Poyarekar
On 12/9/20 6:53 AM, Lukasz Majewski wrote:
> +#define CHECK_TIME64_SIZE(__name, __len) \
> + _Static_assert (sizeof (__name) == __len, "Size of " #__name " != " #__len)
> +
> +#ifdef __USE_TIME_BITS64
> + CHECK_TIME64_SIZE(time_t, 8);
> + CHECK_TIME64_SIZE(struct timespec, 16);
> +#endif
I've lost context here; what branch is this against? glibc master doesn't
have __USE_TIME_BITS64.
If this is in a publicly-visible file, the macro CHECK_TIME64_SIZE would
need to have a reserved name.
I'm leery of the idea of putting checks like this into include files that
users see. If there's a reason a platform cannot support 64-bit time_t even
though __USE_TIME_BITS64 is defined, doesn't this sort of checking belong in
the include file that defines time_t or __TIME_T_TYPE or whatever? That way,
a user who sees the resulting diagnostic will have an easier time figuring
out what exactly went wrong.
^ permalink raw reply [flat|nested] 4+ messages in thread
* Re: [RFC] y2038: test: Add _Static_assert() check when __USE_TIME_BITS64 is defined
2020-12-10 0:42 ` Paul Eggert
@ 2020-12-13 11:48 ` Lukasz Majewski
2020-12-15 18:54 ` Paul Eggert
0 siblings, 1 reply; 4+ messages in thread
From: Lukasz Majewski @ 2020-12-13 11:48 UTC (permalink / raw)
To: Paul Eggert, Joseph Myers, Adhemerval Zanella
Cc: Alistair Francis, Arnd Bergmann, Alistair Francis, GNU C Library,
Florian Weimer, Carlos O'Donell, Stepan Golosunov,
Andreas Schwab, Zack Weinberg, Siddhesh Poyarekar
[-- Attachment #1: Type: text/plain, Size: 2356 bytes --]
Hi Paul,
Thank you for the reply.
> On 12/9/20 6:53 AM, Lukasz Majewski wrote:
>
> > +#define CHECK_TIME64_SIZE(__name, __len) \
> > + _Static_assert (sizeof (__name) == __len, "Size of " #__name "
> > != " #__len) +
> > +#ifdef __USE_TIME_BITS64
> > + CHECK_TIME64_SIZE(time_t, 8);
> > + CHECK_TIME64_SIZE(struct timespec, 16);
> > +#endif
>
> I've lost context here; what branch is this against? glibc master
> doesn't have __USE_TIME_BITS64.
Yes, it doesn't (yet) support it. This will be available when
_TIME_BITS=64 is supported on ports with __WORDSIZE=32 &&
__TIMESIZE!=64.
>
> If this is in a publicly-visible file, the macro CHECK_TIME64_SIZE
> would need to have a reserved name.
Ok. I see - we will stumble upon the reserved namespaces for POSIX
compliant exported headers.
>
> I'm leery of the idea of putting checks like this into include files
> that users see.
The idea here is to prevent compiling user's program on machine, which
will not properly support 64 bit times - for example the underlying
glibc was very old. I do know that this is not preventing from all
threads - as one can just copy binary from some similar system.
It was suggested once (by Adhemerval and Andreas) that _Static_asserts
shall be added to glibc, but I'm a bit confused:
1. If the check is added to exported headers, it will (probably) pollute
the header itself (like in this patch).
2. I could add it into the glibc sources, but then I shall NOT use
__USE_TIME_BITS64 for enabling it, as this is #define from exported
header (and is not visible during glibc build itself). Instead, maybe I
should use __WORDSIZE==32 && __TIMESIZE!=64 as the condition?
> If there's a reason a platform cannot support 64-bit
> time_t even though __USE_TIME_BITS64 is defined, doesn't this sort of
> checking belong in the include file that defines time_t or
> __TIME_T_TYPE or whatever? That way, a user who sees the resulting
> diagnostic will have an easier time figuring out what exactly went
> wrong.
Interesting, thanks for the idea.
Best regards,
Lukasz Majewski
--
DENX Software Engineering GmbH, Managing Director: Wolfgang Denk
HRB 165235 Munich, Office: Kirchenstr.5, D-82194 Groebenzell, Germany
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^ permalink raw reply [flat|nested] 4+ messages in thread
* Re: [RFC] y2038: test: Add _Static_assert() check when __USE_TIME_BITS64 is defined
2020-12-13 11:48 ` Lukasz Majewski
@ 2020-12-15 18:54 ` Paul Eggert
0 siblings, 0 replies; 4+ messages in thread
From: Paul Eggert @ 2020-12-15 18:54 UTC (permalink / raw)
To: Lukasz Majewski, Joseph Myers, Adhemerval Zanella
Cc: Alistair Francis, Arnd Bergmann, Alistair Francis, GNU C Library,
Florian Weimer, Carlos O'Donell, Stepan Golosunov,
Andreas Schwab, Zack Weinberg, Siddhesh Poyarekar
On 12/13/20 3:48 AM, Lukasz Majewski wrote:
> Instead, maybe I
> should use __WORDSIZE==32 && __TIMESIZE!=64 as the condition?
Sounds reasonable. And that could be done with #if and so would generate
better diagnostics for pre-C11 compilers (assuming this stuff is in an
exported header).
^ permalink raw reply [flat|nested] 4+ messages in thread
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2020-12-09 14:53 [RFC] y2038: test: Add _Static_assert() check when __USE_TIME_BITS64 is defined Lukasz Majewski
2020-12-10 0:42 ` Paul Eggert
2020-12-13 11:48 ` Lukasz Majewski
2020-12-15 18:54 ` Paul Eggert
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