[PATCH v3 03/17] tools build: Fix test-clang-bpf-co-re.bin to generate target file

[Ian Rogers]

In tools/build/feature/Makefile, the test-clang-bpf-co-re.bin feature check
compiled test-clang-bpf-co-re.c assembly on stdout and piped it to grep,
but never redirected the matched output to create the target binary ()
on disk.

Because the target file was never created, Kbuild could never cache the
result of the check. Consequently, Make treated the prerequisite as missing
and continuously re-executed the Clang BPF backend compilation check on
every single sub-make evaluation during build startup.

Redirect grep output to  to guarantee the file is created on disk upon
success, allowing Kbuild to perfectly cache the detection result and avoid
redundant sub-make forks.

Assisted-by: Gemini:gemini-3.1-pro-preview
Signed-off-by: Ian Rogers <irogers@xxxxxxxxxx>
---
 tools/build/feature/Makefile | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/tools/build/feature/Makefile b/tools/build/feature/Makefile
index dc828523b50a..c34faccdf28b 100644
--- a/tools/build/feature/Makefile
+++ b/tools/build/feature/Makefile
@@ -385,7 +385,7 @@ $(OUTPUT)test-libzstd.bin:
 
 $(OUTPUT)test-clang-bpf-co-re.bin:
 	$(CLANG) -S -g --target=bpf -o - $(patsubst %.bin,%.c,$(@F)) |	\
-		grep BTF_KIND_VAR
+		grep BTF_KIND_VAR > $@.tmp && mv $@.tmp $@
 
 $(OUTPUT)test-file-handle.bin:
 	$(BUILD)
-- 
2.54.0.563.g4f69b47b94-goog