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Re: ct-ng "kernel version" relation to kernel version


On Friday 28 May 2010 07:38:26 matti kaasinen wrote:
> What relation is between Linux kernel version set in ct-ng
> configuration for toolchain and Linux kernel version to be compiled
> with this toolchain? Should they match (requiring new toolchain for
> every kernel revision) or is it not that exact?

On Linux (and I think it is specific to Linux), the C library has to know
how to talk to the kernel: syscalls and so on... So you need the kernel
headers, sanitised for use by userland (that is, kernel headers with stuff
internal to the kernel removed).

These kernel will define the API between kernel-land and user-land. With
new versions of the kernel, this API will grow new entries, but will never
remove any (except in very, very few occasions, but you can safely ignore
those).

Now, if you run your target with a kernel newer than the one used for
headers, that's OK. You might just not be able to use the whole new fancy
stuff from the kernel (eg. the headers used for the toolchain do not know
about slpice(), but your running kernel does, you won't be able to use
splice() from userland, because the C library will not have detected it
at build time).

Now, if you run a kernel that is older than the one used for the headers,
you are at high risk to not be able to run at all. glibc detects this and
prints a message about it: "too old kernel" (or something like that).

Regards,
Yann E. MORIN.

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