kbuild: add comment about why cmd_shipped uses 'cat'

cmd_shipped uses 'cat' instead of 'cp' for copying a file. The reason is explained in the commit [1], but it was in the pre-git era. $ touch a $ chmod -w a $ cp a b $ cp a b cp: cannot create regular file 'b': Permission denied Add comments so that you can see the reason without looking into the history. [1]: https://git.kernel.org/pub/scm/linux/kernel/git/history/history.git/commit/?id=a70dba8086160449cc94c5bdaff78419b6b8e3c8

Masahiro Yamada committed 5 years ago

Commit 3787b7d1 parent c5849b71 file · +3 −0Browse files

Showing the changes to scripts (1 of 1 file). Show all

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scripts/Makefile.lib+3−0

@@ -252,6 +252,9 @@ quiet_cmd_copy = COPY $@ · 251 unmodified lines
252		252
253	# Shipped files	253	# Shipped files
254	# ===========================================================================	254	# ===========================================================================
		255	# 'cp' preserves permissions. If you use it to copy a file in read-only srctree,
		256	# the copy would be read-only as well, leading to an error when executing the
		257	# rule next time. Use 'cat' instead in order to generate a writable file.
255		258
256	quiet_cmd_shipped = SHIPPED $@	259	quiet_cmd_shipped = SHIPPED $@
257	cmd_shipped = cat $< > $@	260	cmd_shipped = cat $< > $@