[Buildroot] prefix question for kodi.

[Samuel Martin]

Hi all,

On Sat, Jul 9, 2016 at 8:13 PM, daggs <daggs at gmx.com> wrote:
> Greetings,
>
> I'm trying to understand why the kodi's configure prefix param points to /usr and not to the staging dir. can someone help me understand?
> here is the line:

This is not Kodi-specific, this is done like things for many packages
(i.e. for all packages using a decent build-system, e.g. autotools
[1], cmake [2], etc).. So, almost all packages.

For building a target package, the prefix must point to /usr, and not
to the staging dir. because:
1. The --prefix option sets the prefix location in the target
directory, i.e. as its should be at runtime (at runtime in the target
system).
So, in the case of Buildroot, this is not (and must not be) the
absolute location where stuff will be installed.
Note that if you set prefix to STAGING_DIR, I bet your final rootfs
won't look like what you'd expect, and may not work as expected... or
not work at all!
2. To install stuff in a location different from the runtime one, we
use the standard variable DESTDIR (see [3,4])
So, basically when a package using a decent build-system execute an
install rule, it computes the install location like this:
  stuff_install_path = ${DESTDIR}${prefix}/${stuf_dir}
3. We don't (want to) build target packages twice, with only the
--prefix option changed between these 2 builds (i.e. once with
--prefix=$(STAGING_DIR)... and a second time with
--prefix=$(TARGET_DIR)...).
So, from the aforementioned reasons we build each target package once
with the right prefix for the target rootfs, and install twice (if
needed), once with DESTDIR=$(TARGET_DIR) and a second time with
DESTDIR=$(STAGING_DIR), see [3,4].

Note that for the build, things are correctly routed to the staging
dir. thanks to:
- the --sysroot option, optionally with -I.. or -L.. pointing to the
staging tree;
- the Buildroot compiler wrapper that enforce these options to be
correctly set, and also check for poisoning paths (i.e. paths pointing
to standard host system locations, e.g. /usr/lib or /usr/local/lib,
etc).

So, unless you are not lucky packaging a projet that use a
non-standard build-system, or does nasty things at configure-time, you
should not  paid much attention to this prefix option, Buildroot
handles it for you ;-)

Regards,

[1] https://github.com/buildroot/buildroot/blob/master/package/pkg-autotools.mk#L181
[2] https://github.com/buildroot/buildroot/blob/master/package/pkg-cmake.mk#L91
[3] https://github.com/buildroot/buildroot/blob/master/package/pkg-autotools.mk#L159
[4] https://github.com/buildroot/buildroot/blob/master/package/pkg-cmake.mk#L60

-- 
Samuel