[PATCH v2] scripts/tags.sh: fix incompatibility with PCRE2

[Carlos Llamas <cmllamas@google.com>]

Starting with release 10.38 PCRE2 drops default support for using \K in
lookaround patterns as described in [1]. Unfortunately, scripts/tags.sh
relies on such functionality to collect all_compiled_soures() leading to
the following error:

  $ make COMPILED_SOURCE=1 tags
    GEN     tags
  grep: \K is not allowed in lookarounds (but see PCRE2_EXTRA_ALLOW_LOOKAROUND_BSK)

The usage of \K for this pattern was introduced in commit 4f491bb6ea2a
("scripts/tags.sh: collect compiled source precisely") which speeds up
the generation of tags significantly.

In order to fix this issue without compromising the performance we can
switch over to an equivalent sed expression. The same matching pattern
is preserved here except \K is replaced with a backreference \1.

[1] https://www.pcre.org/current/doc/html/pcre2syntax.html#SEC11

Cc: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Cc: Cristian Ciocaltea <cristian.ciocaltea@collabora.com>
Cc: Masahiro Yamada <masahiroy@kernel.org>
Cc: Jialu Xu <xujialu@vimux.org>
Cc: Vipin Sharma <vipinsh@google.com>
Cc: stable@vger.kernel.org
Fixes: 4f491bb6ea2a ("scripts/tags.sh: collect compiled source precisely")
Signed-off-by: Carlos Llamas <cmllamas@google.com>
---
v2: add Fixes tag and cc stable

 scripts/tags.sh | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/scripts/tags.sh b/scripts/tags.sh
index e137cf15aae9..0d045182c08c 100755
--- a/scripts/tags.sh
+++ b/scripts/tags.sh
@@ -91,7 +91,7 @@ all_compiled_sources()
 	{
 		echo include/generated/autoconf.h
 		find $ignore -name "*.cmd" -exec \
-			grep -Poh '(?(?=^source_.* \K).*|(?=^  \K\S).*(?= \\))' {} \+ |
+			sed -n -E 's/^source_.* (.*)/\1/p; s/^  (\S.*) \\/\1/p' {} \+ |
 		awk '!a[$0]++'
 	} | xargs realpath -esq $([ -z "$KBUILD_ABS_SRCTREE" ] && echo --relative-to=.) |
 	sort -u
-- 
2.39.1.637.g21b0678d19-goog