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kbuild,bpf: Pass make jobs' value to pahole

Pass the value of make's -j/--jobs argument to pahole, to avoid out of
memory errors and make pahole respect the "jobs" value of make.

On systems with little memory but many cores, invoking pahole using -j
without argument potentially creates too many pahole instances,
causing an out-of-memory situation. Instead, we should pass make's
"jobs" value as an argument to pahole's -j, which is likely configured
to be (much) lower than the actual core count on such systems.

If make was invoked without -j, either via cmdline or MAKEFLAGS, then
JOBS will be simply empty, resulting in the existing behavior, as
expected.

Signed-off-by: Florian Schmaus <flo@geekplace.eu>
Signed-off-by: Andrii Nakryiko <andrii@kernel.org>
Tested-by: Holger Hoffstätte <holger@applied-asynchrony.com>
Link: https://lore.kernel.org/bpf/20241102100452.793970-1-flo@geekplace.eu

authored by

Florian Schmaus and committed by
Andrii Nakryiko 09048d22 7b6e5bfa

+4 -2
+4 -2
scripts/Makefile.btf
··· 3 3 pahole-ver := $(CONFIG_PAHOLE_VERSION) 4 4 pahole-flags-y := 5 5 6 + JOBS := $(patsubst -j%,%,$(filter -j%,$(MAKEFLAGS))) 7 + 6 8 ifeq ($(call test-le, $(pahole-ver), 125),y) 7 9 8 10 # pahole 1.18 through 1.21 can't handle zero-sized per-CPU vars ··· 14 12 15 13 pahole-flags-$(call test-ge, $(pahole-ver), 121) += --btf_gen_floats 16 14 17 - pahole-flags-$(call test-ge, $(pahole-ver), 122) += -j 15 + pahole-flags-$(call test-ge, $(pahole-ver), 122) += -j$(JOBS) 18 16 19 17 pahole-flags-$(call test-ge, $(pahole-ver), 125) += --skip_encoding_btf_inconsistent_proto --btf_gen_optimized 20 18 21 19 else 22 20 23 21 # Switch to using --btf_features for v1.26 and later. 24 - pahole-flags-$(call test-ge, $(pahole-ver), 126) = -j --btf_features=encode_force,var,float,enum64,decl_tag,type_tag,optimized_func,consistent_func,decl_tag_kfuncs 22 + pahole-flags-$(call test-ge, $(pahole-ver), 126) = -j$(JOBS) --btf_features=encode_force,var,float,enum64,decl_tag,type_tag,optimized_func,consistent_func,decl_tag_kfuncs 25 23 26 24 ifneq ($(KBUILD_EXTMOD),) 27 25 module-pahole-flags-$(call test-ge, $(pahole-ver), 126) += --btf_features=distilled_base