Re: what is the purpose of "--enable-kernel" in configuring glibc?

[Mike Frysinger <vapier at gentoo dot org>]

On Sun, Dec 18, 2005 at 10:44:23AM -0500, Robert P. J. Day wrote:
> On Sat, 17 Dec 2005, Dan Kegel wrote:
> > On 12/17/05, Robert P. J. Day <rpjday@mindspring.com> wrote:
> > >   just out of curiosity, i modified the standard build script and,
> > > in the glibc configure stage, i changed "--enable-kernel=2.4.3" to
> > > 2.6.0, and bad things happened when i was trying to build for
> > > linuxthreads.
> > >
> > >   what is the purpose of that option, and should i be able to change
> > > it to 2.6.0?
> >
> > R, as they say, TFM:
> > http://www.gnu.org/software/libc/manual/html_node/Configuring-and-compiling.html
> 
> oh, i'm well aware of what the words *say*, i'm just not sure what
> they *mean* in terms of actual code generation

it means glibc will cut out any code to support kernel interfaces older
than whatever value you specified

for example, there have been a few diff mount syscalls ... if you told
glibc that it could assume that it would only ever run on linux kernels
2.6.0 or better, it wouldnt include support for the older mount
syscalls since you told it to assume that it need only support the
latest versions that are available in linux 2.6.0

> or how one should choose that value.

that value is up to YOU

if you know for a fact your target will only ever be running linux
2.6.10 or better (say because a driver was added to 2.6.10 that is
absolutely required), then including support in glibc for 2.2.x and
2.4.x kernels is just silly

if however you're say a distro maintainer, you prob want a much more
compatible glibc, so you'd use an older value ... say 2.2.x or 2.4.x
-mike

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