manual: add explanations on limitations about using O=...

Using a relative path for O=... has limitations, since it is interpreted
relative to the Buildroot tree, and thus may lead to unexpected results.

For example, running this:
    make -C buildroot O=my-O

will not create my-O in the current working directory, but as a
sub-directory of the Buildroot tree, here in buildroot/my-O

Explain this in the manual (as is similarly done for BR2_EXTERNAL).
Also add a note that $(O) will be created if missing.

Also change O=.. and -C .. to O=<...> and -C <...> to make it explicit
this is an ellipse, not a relative path.

Reported-by: Jérémy Rosen <jeremy.rosen@openwide.fr>
Signed-off-by: "Yann E. MORIN" <yann.morin.1998@free.fr>
Cc: Samuel Martin <s.martin49@gmail.com>
Reviewed-by: Thomas De Schampheleire <thomas.de.schampheleire@gmail.com>
Acked-by: Samuel Martin <s.martin49@gmail.com>
Signed-off-by: Peter Korsgaard <peter@korsgaard.com>
This commit is contained in:
Yann E. MORIN 2014-02-21 23:17:54 +01:00 committed by Peter Korsgaard
parent 1de64ec8c0
commit a524731012

View file

@ -40,7 +40,13 @@ Or:
$ cd /tmp/build; make O=$PWD -C path/to/buildroot
--------------------
All the output files will be located under +/tmp/build+.
All the output files will be located under +/tmp/build+. If the +O+
path does not exist, Buildroot will create it.
*Note:* the +O+ path can be either an absolute or a relative path, but if it's
passed as a relative path, it is important to note that it is interpreted
relative to the main Buildroot source directory, *not* the current working
directory.
When using out-of-tree builds, the Buildroot +.config+ and temporary
files are also stored in the output directory. This means that you can
@ -48,8 +54,8 @@ safely run multiple builds in parallel using the same source tree as
long as they use unique output directories.
For ease of use, Buildroot generates a Makefile wrapper in the output
directory - so after the first run, you no longer need to pass +O=..+
and +-C ..+, simply run (in the output directory):
directory - so after the first run, you no longer need to pass +O=<...>+
and +-C <...>+, simply run (in the output directory):
--------------------
$ make <target>