On 4/2/21 11:29 AM, James Courtier-Dutton wrote:
> Hi,
>
> Currently, when one builds the linux kernel, it places .o files all
> over the source code tree.
> Is there a way to have the linux kernel build, but place all the .o
> files into a separate build folder?
> Similar to how cmake or ninja work when building C source code.
>
> One possible advantage of this approach is one can then put the build
> folder on a ram disk / tmpfs and be able to compile and test much
> quicker.
That has been available for quite a long time now.
Just use "O=somebuilddir" on the make command line.
$ mkdir build
$ make O=build allnoconfig
$ make O=build all
AFAIK 'somebuilddir' can be a relative path (that's what
I use, in the kernel source tree) or an absolute path,
like O=/tmp/buildit .
>From kernel Makefile "help":
@echo ' make O=dir [targets] Locate all output files in "dir",
including .config'
and from kernel Makefile comments:
# Kbuild will save output files in the current working directory.
# This does not need to match to the root of the kernel source tree.
#
# For example, you can do this:
#
# cd /dir/to/store/output/files; make -f /dir/to/kernel/source/Makefile
#
# If you want to save output files in a different location, there are
# two syntaxes to specify it.
#
# 1) O=
# Use "make O=dir/to/store/output/files/"
#
# 2) Set KBUILD_OUTPUT
# Set the environment variable KBUILD_OUTPUT to point to the output directory.
# export KBUILD_OUTPUT=dir/to/store/output/files/; make
#
# The O= assignment takes precedence over the KBUILD_OUTPUT environment
# variable.
HTH.
--
~Randy
