From: Ben Hutchings <ben@decadent.org.uk>
Date: Sun, 21 Feb 2016 15:33:15 +0000
Subject: 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>
---
--- a/tools/build/feature/test-bpf.c
+++ b/tools/build/feature/test-bpf.c
@@ -41,8 +41,10 @@ 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;
 }