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Message-Id: <20210424115553.396516-1-masahiroy@kernel.org>
Date: Sat, 24 Apr 2021 20:55:53 +0900
From: Masahiro Yamada <masahiroy@...nel.org>
To: linux-kbuild@...r.kernel.org
Cc: Masahiro Yamada <masahiroy@...nel.org>,
Michal Marek <michal.lkml@...kovi.net>,
linux-kernel@...r.kernel.org
Subject: [PATCH] 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
Signed-off-by: Masahiro Yamada <masahiroy@...nel.org>
---
scripts/Makefile.lib | 3 +++
1 file changed, 3 insertions(+)
diff --git a/scripts/Makefile.lib b/scripts/Makefile.lib
index a4fbaf8880b9..1677a7dcd18c 100644
--- a/scripts/Makefile.lib
+++ b/scripts/Makefile.lib
@@ -240,6 +240,9 @@ quiet_cmd_copy = COPY $@
# Shipped files
# ===========================================================================
+# 'cp' preserves permissions. If you use it to copy a file in read-only srctree,
+# the copy would be read-only as well, leading to an error when executing the
+# rule next time. Use 'cat' instead in order to generate a writable file.
quiet_cmd_shipped = SHIPPED $@
cmd_shipped = cat $< > $@
--
2.27.0
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