From: Ben Hutchings <benh@debian.org>
Date: Mon, 16 Sep 2024 01:54:24 +0200
Subject: 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>
---
--- 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)