kbuild: handle old pahole more gracefully when generating BTF

When CONFIG_DEBUG_INFO_BTF is enabled but available version of pahole is too
old to support BTF generation, build script is supposed to emit warning and
proceed with the build. Due to using exit instead of return from BASH function,
existing handling code prematurely exits exit code 0, not completing some of
the build steps. This patch fixes issue by correctly returning just from
gen_btf() function only.

Fixes: e83b9f5 ("kbuild: add ability to generate BTF type info for vmlinux")
Cc: Masahiro Yamada <[email protected]>
Cc: Arnaldo Carvalho de Melo <[email protected]>
Cc: Daniel Borkmann <[email protected]>
Cc: Alexei Starovoitov <[email protected]>
Cc: Yonghong Song <[email protected]>
Cc: Martin KaFai Lau <[email protected]>
Signed-off-by: Andrii Nakryiko <[email protected]>
Acked-by: Song Liu <[email protected]>
Signed-off-by: Daniel Borkmann <[email protected]>

scripts/link-vmlinux.sh

@@ -99,7 +99,7 @@ gen_btf()
 	pahole_ver=$(${PAHOLE} --version | sed -E 's/v([0-9]+)\.([0-9]+)/\1\2/')
 	if [ "${pahole_ver}" -lt "113" ]; then
 		info "BTF" "${1}: pahole version $(${PAHOLE} --version) is too old, need at least v1.13"
-		exit 0
+		return 0
 	fi
 
 	info "BTF" ${1}