tools/build: Remove bpf() run-time check at build time

Forwarded: no

It is not correct to test that a syscall works on the build system's
kernel.  We might be building on an earlier kernel version or with
security restrictions that block bpf().

Signed-off-by: Ben Hutchings <ben@decadent.org.uk>
Gbp-Pq: Topic bugfix/all
Gbp-Pq: Name tools-build-remove-bpf-run-time-check-at-build-time.patch

diff --git a/tools/build/feature/test-bpf.c b/tools/build/feature/test-bpf.c
index 82070eadfc070ffdadc4e729950ab7ae386dfab1..33858735935f87c5f1a6bf5ae50e67895dd9cc78 100644 (file)
--- a/tools/build/feature/test-bpf.c
+++ b/tools/build/feature/test-bpf.c
@@ -35,8 +35,10 @@ int main(void)
        attr.prog_flags = 0;
 
        /*
-        * Test existence of __NR_bpf and BPF_PROG_LOAD.
-        * This call should fail if we run the testcase.
+        * bwh: Don't use the bpf() syscall as we might be building on a
+        * much older kernel.  Do "use" the attr structure here to avoid
+        * a "set but not used" warning.
         */
-       return syscall(__NR_bpf, BPF_PROG_LOAD, &attr, sizeof(attr));
+       (void)&attr;
+       return 0;
 }