kbuild/cert rework for 5.17 breaks build with empty CONFIG_MODULE_SIG_KEY

[Michal Kubecek]

Hello,

while testing merge window snapshots, I noticed that after commit
b8c96a6b466c ("certs: simplify $(srctree)/ handling and remove
config_filename macro"), build with

    CONFIG_MODULE_SIG=y
    CONFIG_MODULE_SIG_FORCE=n
    CONFIG_MODULE_SIG_ALL=n
    CONFIG_MODULE_SIG_KEY=""

(as suggested in Documentation/kbuild/reproducible-builds.rst, section
"Module signing") fails to build as make executes scripts/extract-cert
with only one argument (the unquoted empty string has no effect):

  ...
    certs/extract-cert  certs/signing_key.x509
  Usage: extract-cert <source> <dest>
  make[2]: *** [/home/mike/work/git/kernel-upstream/certs/Makefile:78: certs/signing_key.x509] Error 2
  make[1]: *** [/home/mike/work/git/kernel-upstream/Makefile:1831: certs] Error 2
  make[1]: Leaving directory '/srv/ram/kobj'
  make: *** [Makefile:219: __sub-make] Error 2

Should this be considered a bug or is there a different recommended way
to get reproducible builds now?

Michal

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