On Wed, Oct 18, 2023 at 4:57 AM Andrii Nakryiko <andrii.nakryiko@xxxxxxxxx> wrote: > > On Tue, Oct 17, 2023 at 3:38 AM Masahiro Yamada <masahiroy@xxxxxxxxxx> wrote: > > > > scripts/pahole-flags.sh is executed so many times. > > > > You can check how many times it is invoked during the build, as follows: > > > > $ cat <<EOF >> scripts/pahole-flags.sh > > > echo "scripts/pahole-flags.sh was executed" >&2 > > > EOF > > > > $ make -s > > scripts/pahole-flags.sh was executed > > scripts/pahole-flags.sh was executed > > scripts/pahole-flags.sh was executed > > scripts/pahole-flags.sh was executed > > scripts/pahole-flags.sh was executed > > [ lots of repeated lines suppressed... ] > > > > This scripts is exectuted more than 20 times during the kernel build > > because PAHOLE_FLAGS is a recursively expanded variable and exported > > to sub-processes. > > > > With the GNU Make >= 4.4, it is executed more than 60 times because > > exported variables are also passed to other $(shell ) invocations. > > Without careful coding, it is known to cause an exponential fork > > explosion. [1] > > > > The use of $(shell ) in an exported recursive variable is likely wrong > > because $(shell ) is always evaluated due to the 'export' keyword, and > > the evaluation can occur multiple times by the nature of recursive > > variables. > > > > Convert the shell script to a Makefile, which is included only when > > CONFIG_DEBUG_INFO_BTF=y. > > > > [1]: https://savannah.gnu.org/bugs/index.php?64746 > > > > Signed-off-by: Masahiro Yamada <masahiroy@xxxxxxxxxx> > > --- > > > > Makefile | 4 +--- > > scripts/Makefile.btf | 19 +++++++++++++++++++ > > scripts/pahole-flags.sh | 30 ------------------------------ > > 3 files changed, 20 insertions(+), 33 deletions(-) > > create mode 100644 scripts/Makefile.btf > > delete mode 100755 scripts/pahole-flags.sh > > > > diff --git a/Makefile b/Makefile > > index fed9a6cc3665..eaddec67e5e1 100644 > > --- a/Makefile > > +++ b/Makefile > > @@ -513,8 +513,6 @@ LZ4 = lz4c > > XZ = xz > > ZSTD = zstd > > > > -PAHOLE_FLAGS = $(shell PAHOLE=$(PAHOLE) $(srctree)/scripts/pahole-flags.sh) > > What if we just used := here? Wouldn't it avoid unnecessary multiple executions? Yeah, := is less silly than =. But, I do not like to run the script for non-build targets such as 'make clean', 'make help', etc. Also, when building with CONFIG_DEBUG_INFO_BTF=n, the shell is forked to compute PAHOLE_FLAGS, which we know are unnecessary. -- Best Regards Masahiro Yamada
