kbuild, bpf: Fix BTF reproducibility

pahole 1.22 introduced the -j option for parallel processing, and
kbuild uses it, but this makes its output unreproducible.

pahole 1.27 introduced --btf_features=+reproducible_build which makes
the output reproducible even when -j is used.

Assume that if KBUILD_BUILD_TIMESTAMP is set then a reproducible build
is required, and use both options if available or neither if not.

Signed-off-by: Ben Hutchings <benh@debian.org>
Gbp-Pq: Topic bugfix/all
Gbp-Pq: Name kbuild-bpf-fix-btf-reproducibility.patch

diff --git a/scripts/Makefile.btf b/scripts/Makefile.btf
index b75f09f3f4248d86b553da944f3e5fb7119e3cf4..e622cdd32265b6fd4f5ddb1a3014a8e9bf48417a 100644 (file)
--- a/scripts/Makefile.btf
+++ b/scripts/Makefile.btf
@@ -12,8 +12,6 @@ endif
 
 pahole-flags-$(call test-ge, $(pahole-ver), 121)       += --btf_gen_floats
 
-pahole-flags-$(call test-ge, $(pahole-ver), 122)       += -j
-
 pahole-flags-$(call test-ge, $(pahole-ver), 125)       += --skip_encoding_btf_inconsistent_proto --btf_gen_optimized
 
 else
@@ -27,6 +25,18 @@ endif
 
 endif
 
+# pahole 1.22 introduced the -j option for parallel processing, but
+# this makes its output unreproducible.
+# pahole 1.27 introduced --btf_features=+reproducible_build which
+# makes the output reproducible even when -j is used.
+# Assume that if KBUILD_BUILD_TIMESTAMP is set then a reproducible
+# build is required and we must not use -j alone.
+ifeq ($(KBUILD_BUILD_TIMESTAMP),)
+pahole-flags-$(call test-ge, $(pahole-ver), 122)       += -j
+else
+pahole-flags-$(call test-ge, $(pahole-ver), 127)       += -j --btf_features=+reproducible_build
+endif
+
 pahole-flags-$(CONFIG_PAHOLE_HAS_LANG_EXCLUDE)         += --lang_exclude=rust
 
 export PAHOLE_FLAGS := $(pahole-flags-y)