Re: Relocated Header Directories
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On Mon, Aug 21, 2017 at 02:12:05PM -0500, Dutch Ingraham wrote:
> On 08/21/2017 09:06 AM, Kushal Kumaran wrote:
> > Dutch Ingraham <stoa@gmx.us> writes:
> >
> >> Hi everyone -
> >>
> >> It seems Debian has moved some header directories, like /usr/include/bits (and
> >> sys, and asm, etc.) from /usr/include/ to, e.g., /usr/include/i386-linux-gnu/bits/
> >> (arch-specific).
> >>
> >> My first question is: Why?
> >>
> > This is so that headers that are architecture independent are separated
> > from headers with are architecture dependent. Specifically, that they
> > are available at different paths. This lets you install the headers
> > (and libraries) for different architectures simultaneously, which is
> > essential for debian's multiarch support.
> Thanks for the response. Since both you and Tomas are saying the same
> thing,
> maybe I'm not understanding something. For example, Fedora (and Gentoo,
> etc. )
> also installs glibc for both 32- and 64-bit on the same machine, but
> they have not
> relocated these header files. So are you saying this was just Debian's
> method
> of solving the multi-arch issue, and other distributions solved in some
> other way?
Exactly. In RH, the "default" is under /usr/lib, /usr/include, in Debian,
there's for every installed architecture /usr/*/$ARCH. This provides an
uniform structure, independent of the "default" arch. The change is a bit
more difficult, but the result is cleaner, as far as I understand.
This eases co-installing cross compilers for other architectures too,
> >> My second question is: How does this work? There are no symlinks, yet a file
> >> like /usr/include/signal.h, has the standard "#include <bits/sigset.h>", yet
> >> that path does not exist with the change noted above. So how is this file
> >> included?
> >>
> >> Any enlightenment is appreciated.
> > There are several directories configured for searching header files.
> > The command "gcc -xc -E -v - < /dev/null" will print those paths out.
> > For my system, the directories are:
> >
> > /usr/lib/gcc/x86_64-linux-gnu/6/include
> > /usr/local/include
> > /usr/lib/gcc/x86_64-linux-gnu/6/include-fixed
> > /usr/include/x86_64-linux-gnu
> > /usr/include
> >
> > The list will be different for you because you appear to be running
> > i386.
> I'm not seeing some of these paths in vanilla gcc. Does this mean
> Debian patched
> gcc as well to add the "Debian" path of /usr/include/x86_64-linux-gnu/ ?
I think it is a configuration option when building gcc and friends.
Cheers
- -- tomás
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