[PATCH AUTOSEL 5.10 32/88] kbuild: sink stdout from cmd for silent build

[PATCH AUTOSEL 5.10 32/88] kbuild: sink stdout from cmd for silent build

[Sasha Levin]

From: Masahiro Yamada <masahiroy@kernel.org>

[ 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>
---
 scripts/Kbuild.include | 7 ++++++-
 1 file changed, 6 insertions(+), 1 deletion(-)

diff --git a/scripts/Kbuild.include b/scripts/Kbuild.include
index 08e011175b4c..0d6e11820791 100644
--- a/scripts/Kbuild.include
+++ b/scripts/Kbuild.include
@@ -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
-- 
2.30.2

[PATCH AUTOSEL 5.10 75/88] kbuild: mkcompile_h: consider timestamp if KBUILD_BUILD_TIMESTAMP is set

[Sasha Levin]

From: Matthias Maennich <maennich@google.com>

[ Upstream commit a979522a1a88556e42a22ce61bccc58e304cb361 ]

To avoid unnecessary recompilations, mkcompile_h does not regenerate
compile.h if just the timestamp changed.
Though, if KBUILD_BUILD_TIMESTAMP is set, an explicit timestamp for the
build was requested, in which case we should not ignore it.

If a user follows the documentation for reproducible builds [1] and
defines KBUILD_BUILD_TIMESTAMP as the git commit timestamp, a clean
build will have the correct timestamp. A subsequent cherry-pick (or
amend) changes the commit timestamp and if an incremental build is done
with a different KBUILD_BUILD_TIMESTAMP now, that new value is not taken
into consideration. But it should for reproducibility.

Hence, whenever KBUILD_BUILD_TIMESTAMP is explicitly set, do not ignore
UTS_VERSION when making a decision about whether the regenerated version
of compile.h should be moved into place.

[1] https://www.kernel.org/doc/html/latest/kbuild/reproducible-builds.html

Signed-off-by: Matthias Maennich <maennich@google.com>
Signed-off-by: Masahiro Yamada <masahiroy@kernel.org>
Signed-off-by: Sasha Levin <sashal@kernel.org>
---
 scripts/mkcompile_h | 14 +++++++++++---
 1 file changed, 11 insertions(+), 3 deletions(-)

diff --git a/scripts/mkcompile_h b/scripts/mkcompile_h
index 4ae735039daf..a72b154de7b0 100755
--- a/scripts/mkcompile_h
+++ b/scripts/mkcompile_h
@@ -70,15 +70,23 @@ UTS_VERSION="$(echo $UTS_VERSION $CONFIG_FLAGS $TIMESTAMP | cut -b -$UTS_LEN)"
 # Only replace the real compile.h if the new one is different,
 # in order to preserve the timestamp and avoid unnecessary
 # recompilations.
-# We don't consider the file changed if only the date/time changed.
+# We don't consider the file changed if only the date/time changed,
+# unless KBUILD_BUILD_TIMESTAMP was explicitly set (e.g. for
+# reproducible builds with that value referring to a commit timestamp).
 # A kernel config change will increase the generation number, thus
 # causing compile.h to be updated (including date/time) due to the
 # changed comment in the
 # first line.
 
+if [ -z "$KBUILD_BUILD_TIMESTAMP" ]; then
+   IGNORE_PATTERN="UTS_VERSION"
+else
+   IGNORE_PATTERN="NOT_A_PATTERN_TO_BE_MATCHED"
+fi
+
 if [ -r $TARGET ] && \
-      grep -v 'UTS_VERSION' $TARGET > .tmpver.1 && \
-      grep -v 'UTS_VERSION' .tmpcompile > .tmpver.2 && \
+      grep -v $IGNORE_PATTERN $TARGET > .tmpver.1 && \
+      grep -v $IGNORE_PATTERN .tmpcompile > .tmpver.2 && \
       cmp -s .tmpver.1 .tmpver.2; then
    rm -f .tmpcompile
 else
-- 
2.30.2