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====== Switch back to glibc from musl ======
<note>This is relevant to [[resources:tools-software:linuxdsp:releaselandingpages:3.0.0|Linux for ADSP-SC5xx Processors 3.0.0]] only. Earlier version do not feature this choice, and on later versions this has been simplified a lot</note>

This page provides instructions for reverting a toolchain change introduced in version 3.0.0 of Linux for ADSP-SC5xx Processors.


===== Why was that changed? =====
It is described in the upstream repo of U-Boot: [[https://github.com/u-boot/u-boot/blob/master/doc/README.falcon | U-Boot Falcon Mode]]. In short, it's a way to shorten the boot time by allowing the SPL (Secondary Program Loader) to boot the kernel directly, without loading the full bootloader.

A change has been made to reduce the rootFS size as seen here [[https://github.com/analogdevicesinc/lnxdsp-adi-meta/commit/540ce488d3364caf4e783f018b12087857bbdebf | here]]. Part of that change is to depend on the ''poky-tiny'' DISTRO instead of ''poky''.  The ''poky-tiny'' uses **''musl''** to reduce the overall image size. That means that the SDK that is built by Yocto on version 3.0.0 uses **''musl''** libc while prior to that, it generated a **''glibc''** toolchain. 

Although **''musl''** is a lot leaner than **''glibc''**, they are largely compatible. There is [[https://wiki.musl-libc.org/functional-differences-from-glibc.html | a number of functional differences listed on wiki.musl-libc.org]] for further reading.

===== How to switch back? =====
Switching back to **''glibc''** is as simple as a single commit revert on the ''meta-adi'' layer. Here's how to do that:

=== Prepare the build ===
Follow the steps in the [[:resources:tools-software:linuxdsp:releaselandingpages:3.0.0 | 3.0.0 Quickstart guide]] up to and including the '**Preparing the buildtool'** step.

=== Revert the commit ===
A single commit must be reverted to fall back into **''glibc''** (''$PROJECTDIR'' being whatever you called your project upon creating it):

<code bash>
$ cd $PROJECTDIR/sources/meta-adi/

$ git revert 540ce488d3364caf4e783f018b12087857bbdebf
</code>

At this point you need to edit ''meta-adi-adsp-sc5xx/classes/adsp-sc5xx.bbclass'' with your favorite text editor, e.g.

<code bash>
$ vi meta-adi-adsp-sc5xx/classes/adsp-sc5xx.bbclass
</code>

and delete the bottom conflict text:

<code diff>
<<<<<<< HEAD

IMAGE_FSTYPES:append = " tar.xz jffs2 "

#For some reason on poky-tiny, INIT_MANAGER="systemd" does not appear to work
#For now, let's relink directly to systemd
fakeroot do_set_init(){
    rm -rf ${IMAGE_ROOTFS}/sbin/init
    ln -s /lib/systemd/systemd ${IMAGE_ROOTFS}/sbin/init
}

addtask do_set_init after do_rootfs before do_image
=======
>>>>>>> parent of 540ce48... Further reduce RFS size via poky-tiny.conf instead of poky.conf
</code>

=== Proceed with building. ===
You can now proceed with the rest of the Quickstart guide instructions.

<note important>Doing this will increase the FIT+RFS sizes such that the SPI boot paths no longer work because of insufficient space on the smaller board flashes (16MB or 32MB).  TFTP/NFS/MMC/SD should still work.</note>
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