[PATCH] build system: Make it possible to build with 64bit time_t

[Denys Vlasenko]

Applied, thank you!

On Thu, Apr 20, 2023 at 2:13 PM Uwe Kleine-König <uwe at kleine-koenig.org> wrote:
>
> From: Uwe Kleine-König <u.kleine-koenig at pengutronix.de>
>
> On most 32bit architectures time_t (and a few other time related types)
> are a signed 32bit wide integer type.
> As a consequence they can only represent dates between
>
>         Fri Dec 13 08:45:52 PM UTC 1901
>
> (-0x80000000 seconds before Jan 1 1970) and
>
>         Tue Jan 19 03:14:07 AM UTC 2038
>
> (0x7fffffff seconds after Jan 1 1970). Given that some machines that are
> built today have an expected lifetime of >15 years, this needs to be
> extended. To to that, define the cpp symbol _TIME_BITS to 64 which
> results in some magic in glibc to make time_t (and the few other time
> related types) 64 bit wide.
>
> This new switch CONFIG_TIME64 is in the spirit of CONFIG_LFS and only
> expected to have the expected effect with glibc. On musl for examples
> time_t already defaults to 64bit wide types.
> ---
>  Config.in      | 10 ++++++++++
>  Makefile.flags |  1 +
>  2 files changed, 11 insertions(+)
>
> diff --git a/Config.in b/Config.in
> index a98a8b15b854..214eba54630e 100644
> --- a/Config.in
> +++ b/Config.in
> @@ -108,6 +108,16 @@ config LFS
>         programs that can benefit from large file support include dd, gzip,
>         cp, mount, tar.
>
> +config TIME64
> +       bool "Support 64bit wide time types"
> +       default y
> +       depends on LFS
> +       help
> +       Make times later than 2038 representable for several libc syscalls
> +       (stat, clk_gettime etc.). Note this switch is specific to glibc and has
> +       no effect on platforms that already use 64bit wide time types (i.e. all
> +       64bit archs and some selected 32bit archs (currently riscv and x32)).
> +
>  config PAM
>         bool "Support PAM (Pluggable Authentication Modules)"
>         default n
> diff --git a/Makefile.flags b/Makefile.flags
> index c34356230a9f..e17defbd00f9 100644
> --- a/Makefile.flags
> +++ b/Makefile.flags
> @@ -15,6 +15,7 @@ CPPFLAGS += \
>         -include include/autoconf.h \
>         -D_GNU_SOURCE -DNDEBUG \
>         $(if $(CONFIG_LFS),-D_LARGEFILE_SOURCE -D_LARGEFILE64_SOURCE -D_FILE_OFFSET_BITS=64) \
> +       $(if $(CONFIG_TIME64),-D_TIME_BITS=64) \
>         -DBB_VER=$(squote)$(quote)$(BB_VER)$(quote)$(squote)
>
>  CFLAGS += $(call cc-option,-Wall,)
>
> base-commit: e512aeb0fb3c585948ae6517cfdf4a53cf99774d
> --
> 2.39.2
>
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