[PATCH v2] 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.

v2:
- Add BLANK() macro for better readability of generated headers
(suggested by Nathan Chancellor).

Fixes: 7dd47b95b0f5 ("kbuild: consolidate redundant sed script ASM offset generation")
Signed-off-by: Dmitry Kandybka <d.kandybka@gmail.com>
---
 include/linux/kbuild.h | 2 +-
 scripts/Makefile.lib   | 6 +++---
 2 files changed, 4 insertions(+), 4 deletions(-)

diff --git a/include/linux/kbuild.h b/include/linux/kbuild.h
index e7be517aaaf6..118568971fdf 100644
--- a/include/linux/kbuild.h
+++ b/include/linux/kbuild.h
@@ -5,7 +5,7 @@
 #define DEFINE(sym, val) \
 	asm volatile("\n.ascii \"->" #sym " %0 " #val "\"" : : "i" (val))
 
-#define BLANK() asm volatile("\n.ascii \"->\"" : : )
+#define BLANK() do { asm volatile ("\n.ascii \"->BLANK()\"" : : ); } while (0)
 
 #define OFFSET(sym, str, mem) \
 	DEFINE(sym, offsetof(struct str, mem))
diff --git a/scripts/Makefile.lib b/scripts/Makefile.lib
index 0a4fdd8bd975..96c2ec50f06e 100644
--- a/scripts/Makefile.lib
+++ b/scripts/Makefile.lib
@@ -493,9 +493,9 @@ 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; \
+	s:->BLANK()::p;}'
 endef
 
 # Use filechk to avoid rebuilds when a header changes, but the resulting file
-- 
2.54.0