Re: [Buildroot] [git commit] docs/manual: add a FAQ entry about Y2038 support

[Peter Korsgaard <peter@korsgaard.com>]

>>>>> "Thomas" == Thomas Petazzoni via buildroot <buildroot@buildroot.org> writes:

 > commit: https://git.buildroot.net/buildroot/commit/?id=f10f47ff2873d2259e4a03060e9cf0fd1b0f05e0
 > branch: https://git.buildroot.net/buildroot/commit/?id=refs/heads/master

 > This was reviewed in person by Arnout.

 > Signed-off-by: Thomas Petazzoni <thomas.petazzoni@bootlin.com>
 > ---
 >  docs/manual/faq-troubleshooting.adoc | 28 ++++++++++++++++++++++++++++
 >  1 file changed, 28 insertions(+)

 > diff --git a/docs/manual/faq-troubleshooting.adoc b/docs/manual/faq-troubleshooting.adoc
 > index b08bf9bc4a..a61276d4c5 100644
 > --- a/docs/manual/faq-troubleshooting.adoc
 > +++ b/docs/manual/faq-troubleshooting.adoc
 > @@ -242,3 +242,31 @@ help reduce the build time:
 
 >   * Experiment with top-level parallel build, see
 >     xref:top-level-parallel-build[].
 > +
 > +[[faq-2038]]
 > +=== How does Buildroot support Y2038?
 > +
 > +There are multiple situations to consider:
 > +
 > + * On 64-bit architectures, there is no problem, as +time_t+ has
 > +   always been 64-bit.

 > +
 > + * On 32-bit architectures, the situation depends on the C library:
 > +
 > + ** With _uclibc-ng_, there is no support for 64-bit +time_t+ on
 > +    32-bit architectures, so systems using _uclibc-ng_ on 32-bit
 > +    platforms will not be Y2038 compatible.
 > +
 > + ** With _musl_, 64-bit +time_t+ has always been used on 32-bit
 > +    architectures, so systems using _musl_ on 32-bit platforms are
 > +    Y2038 compatible.

"has always been used" is not really true, it was added in musl 1.2.0:
https://musl.libc.org/time64.html

Maybe we should say "always uses" instead?

 > +
 > + ** With _glibc_, 64-bit +time_t+ on 32-bit architectures is enabled
 > +    by the Buildroot option +BR2_TIME_BITS_64+. With this option
 > +    enabled, systems using _glibc_ on 32-bit platforms are Y2038
 > +    compatible.
 > +
 > +Note that the above only comments about the capabilities of the C
 > +library. Individual user-space libraries or applications, even when
 > +built in a Y2038-compatible setup, can exhibit incorrect behavior if
 > +they do not make correct use of the time APIs and types.

We should probably also mention the kernel dependency, E.G. the above is
only correct if using Linux 5.6+ kernel / headers:

https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/commit/?id=22b17db4ea05561c7c8e4d770f10751e22e339f9

-- 
Bye, Peter Korsgaard
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