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kbuild: sink stdout from cmd for silent build

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[ Upstream commit 174a1dcc96429efce4ef7eb2f5c4506480da2182 ]

When building with 'make -s', no output to stdout should be printed.

As Arnd Bergmann reported [1], mkimage shows the detailed information
of the generated images.

I think this should be suppressed by the 'cmd' macro instead of by
individual scripts.

Insert 'exec >/dev/null;' in order to redirect stdout to /dev/null for
silent builds.

[Note about this implementation]

'exec >/dev/null;' may look somewhat tricky, but this has a reason.

Appending '>/dev/null' at the end of command line is a common way for
redirection, so I first tried this:

  cmd = @set -e; $(echo-cmd) $(cmd_$(1)) >/dev/null

... but it would not work if $(cmd_$(1)) itself contains a redirection.

For example, cmd_wrap in scripts/Makefile.asm-generic redirects the
output from the 'echo' command into the target file.

It would be expanded into:

  echo "#include <asm-generic/$*.h>" > $@ >/dev/null

Then, the target file gets empty because the string will go to /dev/null
instead of $@.

Next, I tried this:

  cmd = @set -e; $(echo-cmd) { $(cmd_$(1)); } >/dev/null

The form above would be expanded into:

  { echo "#include <asm-generic/$*.h>" > $@; } >/dev/null

This works as expected. However, it would be a syntax error if
$(cmd_$(1)) is empty.

When CONFIG_TRIM_UNUSED_KSYMS is disabled, $(call cmd,gen_ksymdeps) in
scripts/Makefile.build would be expanded into:

  set -e;  { ; } >/dev/null

..., which causes an syntax error.

I also tried this:

  cmd = @set -e; $(echo-cmd) ( $(cmd_$(1)) ) >/dev/null

... but this causes a syntax error for the same reason.

So, finally I adopted:

  cmd = @set -e; $(echo-cmd) exec >/dev/null; $(cmd_$(1))

[1]: https://lore.kernel.org/lkml/20210514135752.2910387-1-arnd@kernel.org/

Signed-off-by: Masahiro Yamada <masahiroy@kernel.org>
Signed-off-by: Sasha Levin <sashal@kernel.org>
This commit is contained in:
Masahiro Yamada 2021-05-17 16:03:13 +09:00 committed by Greg Kroah-Hartman
parent 27582c9fa2
commit 3f09485699
1 changed files with 6 additions and 1 deletions
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7
scripts/Kbuild.include
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@ -174,8 +174,13 @@ clean := -f $(srctree)/scripts/Makefile.clean obj
echo-cmd = $(if $($(quiet)cmd_$(1)),\
echo ' $(call escsq,$($(quiet)cmd_$(1)))$(echo-why)';)
# sink stdout for 'make -s'
redirect :=
quiet_redirect :=
silent_redirect := exec >/dev/null;
# printing commands
cmd = @set -e; $(echo-cmd) $(cmd_$(1))
cmd = @set -e; $(echo-cmd) $($(quiet)redirect) $(cmd_$(1))
###
# if_changed - execute command if any prerequisite is newer than