[PATCH 5.13 266/800] kbuild: skip per-CPU BTF generation for pahole v1.18-v1.21

[Greg Kroah-Hartman]

From: Andrii Nakryiko <andrii@xxxxxxxxxx>

[ Upstream commit a0b8200d06ad6450c179407baa5f0f52f8cfcc97 ]

Commit "mm/page_alloc: convert per-cpu list protection to local_lock" will
introduce a zero-sized per-CPU variable, which causes pahole to generate
invalid BTF.  Only pahole versions 1.18 through 1.21 are impacted, as
before 1.18 pahole doesn't know anything about per-CPU variables, and 1.22
contains the proper fix for the issue.

Luckily, pahole 1.18 got --skip_encoding_btf_vars option disabling BTF
generation for per-CPU variables in anticipation of some unanticipated
problems.  So use this escape hatch to disable per-CPU var BTF info on
those problematic pahole versions.  Users relying on availability of
per-CPU var BTFs would need to upgrade to pahole 1.22+, but everyone won't
notice any regressions.

Link: https://lkml.kernel.org/r/20210530002536.3193829-1-andrii@xxxxxxxxxx
Signed-off-by: Andrii Nakryiko <andrii@xxxxxxxxxx>
Acked-by: Mel Gorman <mgorman@xxxxxxxxxxxxxxxxxxx>
Cc: Arnaldo Carvalho de Melo <acme@xxxxxxxxxx>
Cc: Hao Luo <haoluo@xxxxxxxxxx>
Cc: Michal Suchanek <msuchanek@xxxxxxx>
Cc: Jiri Olsa <jolsa@xxxxxxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
Signed-off-by: Linus Torvalds <torvalds@xxxxxxxxxxxxxxxxxxxx>
Signed-off-by: Sasha Levin <sashal@xxxxxxxxxx>
---
 scripts/link-vmlinux.sh | 4 ++++
 1 file changed, 4 insertions(+)

diff --git a/scripts/link-vmlinux.sh b/scripts/link-vmlinux.sh
index 0e0f6466b18d..475faa15854e 100755
--- a/scripts/link-vmlinux.sh
+++ b/scripts/link-vmlinux.sh
@@ -235,6 +235,10 @@ gen_btf()
 
 	vmlinux_link ${1}
 
+	if [ "${pahole_ver}" -ge "118" ] && [ "${pahole_ver}" -le "121" ]; then
+		# pahole 1.18 through 1.21 can't handle zero-sized per-CPU vars
+		extra_paholeopt="${extra_paholeopt} --skip_encoding_btf_vars"
+	fi
 	if [ "${pahole_ver}" -ge "121" ]; then
 		extra_paholeopt="${extra_paholeopt} --btf_gen_floats"
 	fi
-- 
2.30.2