Re: [Y2038] [PATCH 5/9] y2038: introduce CONFIG_64BIT_TIME

[Ben Hutchings]

On Fri, 2017-11-10 at 14:42 -0800, Deepa Dinamani wrote:
> From: Arnd Bergmann <arnd@xxxxxxxx>
> 
> There are a total of 53 system calls (aside from ioctl) that pass a time_t
> or derived data structure as an argument, and in order to extend time_t
> to 64-bit, we have to replace them with new system calls and keep providing
> backwards compatibility.
> 
> To avoid adding completely new and untested code for this purpose, we
> introduce a new CONFIG_64BIT_TIME symbol. Every architecture that supports
> new 64 bit time_t syscalls enables this config via ARCH_HAS_64BIT_TIME.
> 
> After this is done for all architectures, the CONFIG_64BIT_TIME symbol
> can be made a user-selected option, to enable users to build a kernel
> that only provides y2038-safe system calls by making 32 time_t syscalls
> conditionally included based on the above config.

I don't understand why we would want to change the semantics of
CONFIG_64BIT_TIME symbol from "enable 64-bit time support" to "disable
32-bit time support".

Why not add two config symbols:

configÂ32BIT_TIME
	def_bool COMPAT || !64BIT

config 64BIT_TIME
	def_bool ARCH_HAS_64BIT_TIME

and then make 32BIT_TIME user-configurable later?

> Signed-off-by: Arnd Bergmann <arnd@xxxxxxxx>
> Signed-off-by: Deepa Dinamani <deepa.kernel@xxxxxxxxx>
> ---
> Âarch/Kconfig | 11 +++++++++++
> Â1 file changed, 11 insertions(+)
> 
> diff --git a/arch/Kconfig b/arch/Kconfig
> index 8911ff37335a..3266ac1a4ff7 100644
> --- a/arch/Kconfig
> +++ b/arch/Kconfig
> @@ -875,6 +875,17 @@ config OLD_SIGACTION
> Âconfig COMPAT_OLD_SIGACTION
> Â	bool
> Â
> +config ARCH_HAS_64BIT_TIME
> +	def_bool n
> +
> +config CONFIG_64BIT_TIME

The CONFIG_ prefix is added by kconfig scripts and shouldn't be used in
the Kconfig file.

Ben.

> +	def_bool ARCH_HAS_64BIT_TIME
> +	help
> +	ÂÂThis should be selected by all architectures that need to support
> +	ÂÂnew system calls with a 64-bit time_t. This is relevant on all 32-bit
> +	ÂÂarchitectures, and 64-bit architectures as part of compat syscall
> +	ÂÂhandling.
> +
> Âconfig ARCH_NO_COHERENT_DMA_MMAP
> Â	bool
> Â

-- 
Ben Hutchings
Software Developer, Codethink Ltd.