emerge failed because I don't have /usr/src/linux?

[fpemud]

fpemud-workstation codes # USE=minimal emerge -1 mono
Calculating dependencies... done!

>>> Verifying ebuild manifests
>>> Running pre-merge checks for dev-lang/mono-4.2.3.4
* Determining the location of the kernel source code
* Unable to find kernel sources at /usr/src/linux
* Please make sure that /usr/src/linux points at your running kernel,
* (or the kernel you wish to build against).
* Alternatively, set the KERNEL_DIR environment variable to the kernel sources location
* Unable to calculate Linux Kernel version for build, attempting to use running version
* Could not find a usable .config in the kernel source directory.
* Please ensure that /usr/src/linux points to a configured set of Linux sources.
* If you are using KBUILD_OUTPUT, please set the environment var so that
* it points to the necessary object directory so that it might find .config.
* ERROR: dev-lang/mono-4.2.3.4::gentoo failed (pretend phase):
* Kernel not configured; no .config found in
*
* Call stack:
* ebuild.sh, line 133: Called pkg_pretend
* mono-4.2.3.4.ebuild, line 44: Called check_extra_config
* linux-info.eclass, line 734: Called require_configured_kernel
* linux-info.eclass, line 297: Called die
* The specific snippet of code:
* die "Kernel not configured; no .config found in ${KV_OUT_DIR}"
*
* If you need support, post the output of `emerge --info '=dev-lang/mono-4.2.3.4::gentoo'`,
* the complete build log and the output of `emerge -pqv '=dev-lang/mono-4.2.3.4::gentoo'`.
* The complete build log is located at '/var/tmp/portage/dev-lang/mono-4.2.3.4/temp/build.log'.
* The ebuild environment file is located at '/var/tmp/portage/dev-lang/mono-4.2.3.4/temp/die.env'.
* Working directory: '/usr/lib64/python3.3/site-packages'
* S: '/var/tmp/portage/dev-lang/mono-4.2.3.4/work/mono-4.2.3'


In my opinion, /proc/config.gz should be the fall back for /usr/src/linux/.config, shouldn't it?
Or is it a sin that I don't keep /usr/src/linux?

[Roman_Gruber]

no

gentoo needs (official way)

e.g. gentoo sources installed and pointing to that installed gentoo source + valid kernel config there

thats it.

you can have /usr/src/linux point to any valid kernel sources.

---

many ebuilds depends on

[khayyam]

fpemud ...

you can probably work around it like so: