[yocto] Documentation on WORKDIR

[Guenzel, Robert]

Hello,

I am currently starting to work with Yocto and I am having a bit of a hard time to figure out how the two documented versions of WORKDIR come into existence.

The doc states:
"""
For packages that are not dependent on a particular machine, WORKDIR is defined as follows:
   ${TMPDIR}/work/${PACKAGE_ARCH}-poky-${TARGET_OS}/${PN}/${PV}-${PR}
[...]
For packages that are dependent on a particular machine, WORKDIR is defined slightly different:
  ${TMPDIR}/work/${MACHINE}-poky-${TARGET_OS}/${PN}/${PV}-${PR}
"""

Now I tried to figure out how a package becomes machine dependent, and I could not find this.
After poking around in already existing layers and recipes, I think that the doc is misleading.

It appears to me that only one version exists, which is:
  ${TMPDIR}/work/${PACKAGE_ARCH}-poky-${TARGET_OS}/${PN}/${PV}-${PR}

And in case a package is machine specific, one overrides the default PACKAGE_ARCH with (the undocumented)
variable MACHINE_ARCH like this:
  PACKAGE_ARCH="${MACHINE_ARCH}"
(where I believe that MACHINE_ARCH is equal to MACHINE??)

Which will then lead to a WORKDIR that looks like ${TMPDIR}/work/${MACHINE}-poky-${TARGET_OS}/${PN}/${PV}-${PR}
(but still is ${TMPDIR}/work/${PACKAGE_ARCH}-poky-${TARGET_OS}/${PN}/${PV}-${PR}).

(there are some bbclasses that do this, and there are some recipes that do it).

Being pretty new to Yocto, I have the feeling that I simply got it all wrong, so before posting bugs or something, I'd wanted to know
if anybody could shed light on this.

thanks and best regards
  Robert

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