On 10/18/23 12:19, Masahiro Yamada 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 executed 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>
Reviewed-by: Alan Maguire <alan.maguire@xxxxxxxxxx>
Tested-by: Alan Maguire <alan.maguire@xxxxxxxxxx>
Reviewed-by: Nicolas Schier <n.schier@xxxxxx>
Tested-by: Miguel Ojeda <ojeda@xxxxxxxxxx>
Acked-by: Miguel Ojeda <ojeda@xxxxxxxxxx>
---
[...]
@@ -1002,6 +999,7 @@ KBUILD_CPPFLAGS += $(call cc-option,-fmacro-prefix-map=$(srctree)/=)
# include additional Makefiles when needed
include-y := scripts/Makefile.extrawarn
include-$(CONFIG_DEBUG_INFO) += scripts/Makefile.debug
+include-$(CONFIG_DEBUG_INFO_BTF)+= scripts/Makefile.btf
Would've used a tab, for legibility sake.
include-$(CONFIG_KASAN) += scripts/Makefile.kasan
include-$(CONFIG_KCSAN) += scripts/Makefile.kcsan
include-$(CONFIG_KMSAN) += scripts/Makefile.kmsan
[...]
Reviewed-by: Martin Rodriguez Reboredo <yakoyoku@xxxxxxxxx>
