[PATCH] kbuild: Makefile.lib: fix offsets generation with debug info

[Dmitry Kandybka <d.kandybka@gmail.com>]

When debug information is enabled (e.g. -ggdb3), the assembler
output file (e.g. kernel/sched/rq-offsets.s) contains additional
directives such as .ascii with offset info and debug metadata.

For example:

    .ascii "->RQ_nr_pinned $3048 offsetof(struct rq, nr_pinned)"  #
    ...
    .ascii "->func); __data = (it_func_ptr)->data; ((void(*)(void *, pro"

The current sed-offsets macro uses [^ ]* to match constant names,
which is too permissive and can match unexpected characters when
debug directives are present. Additionally, the fallback command
's:->::; p;' strips '->' from any unmatched line and prints it,
which causes debug metadata to leak into the generated header
file (include/generated/rq-offsets.h), breaking the build.

Replace [^ ]* with [[:alnum:]_]* to match only valid C identifiers,
and remove the fallback 's:->::' command so that only successfully
transformed lines are emitted into the generated header.

Fixes: 7dd47b95b0f5 ("kbuild: consolidate redundant sed script ASM offset generation")
Signed-off-by: Dmitry Kandybka <d.kandybka@gmail.com>
---
 scripts/Makefile.lib | 5 ++---
 1 file changed, 2 insertions(+), 3 deletions(-)

diff --git a/scripts/Makefile.lib b/scripts/Makefile.lib
index 0a4fdd8bd975..32251eb6ca33 100644
--- a/scripts/Makefile.lib
+++ b/scripts/Makefile.lib
@@ -493,9 +493,8 @@ quiet_cmd_zstd22_with_size = ZSTD22  $@
 # the .ascii directive whereas GCC keeps the <space> as-is.
 define sed-offsets
 	's:^[[:space:]]*\.ascii[[:space:]]*"\(.*\)".*:\1:; \
-	/^->/{s:->#\(.*\):/* \1 */:; \
-	s:^->\([^ ]*\) [\$$#]*\([^ ]*\) \(.*\):#define \1 \2 /* \3 */:; \
-	s:->::; p;}'
+	/^->/{s:->#\(.*\):/* \1 */:p; \
+	s:^->\([[:alnum:]_]*\) [\$$#]*\([^ ]*\) \(.*\):#define \1 \2 /* \3 */:p;}'
 endef
 
 # Use filechk to avoid rebuilds when a header changes, but the resulting file
-- 
2.54.0