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

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

[Andrii Nakryiko]

Commit "mm/page_alloc: convert per-cpu list protection to local_lock"
introduced 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.

Cc: Mel Gorman <mgorman@techsingularity.net>
Cc: Arnaldo Carvalho de Melo <acme@redhat.com>
Cc: Hao Luo <haoluo@google.com>
Signed-off-by: Andrii Nakryiko <andrii@kernel.org>
---
 scripts/link-vmlinux.sh | 4 ++++
 1 file changed, 4 insertions(+)

diff --git a/scripts/link-vmlinux.sh b/scripts/link-vmlinux.sh
index 3b342b0b0b38..66e7053aa907 100755
--- a/scripts/link-vmlinux.sh
+++ b/scripts/link-vmlinux.sh
@@ -233,6 +233,10 @@ 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

Re: [PATCH] kbuild: skip per-CPU BTF generation for pahole v1.18-v1.21

[Mel Gorman]

On Sat, May 29, 2021 at 05:25:36PM -0700, Andrii Nakryiko wrote:
> Commit "mm/page_alloc: convert per-cpu list protection to local_lock"
> introduced 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.
> 
> Cc: Mel Gorman <mgorman@techsingularity.net>
> Cc: Arnaldo Carvalho de Melo <acme@redhat.com>
> Cc: Hao Luo <haoluo@google.com>
> Signed-off-by: Andrii Nakryiko <andrii@kernel.org>

Acked-by: Mel Gorman <mgorman@techsingularity.net>

-- 
Mel Gorman
SUSE Labs