[PATCH bpf-next V2] bpf: use -Wno-address-of-packed-member when building with GCC

["Jose E. Marchesi" <jose.marchesi@xxxxxxxxxx>]

[Differences from V1:
- Now pragmas are used in testfiles instead of flags
  in Makefile.]

GCC implements the -Wno-address-of-packed-member warning, which is
enabled by -Wall, that warns about taking the address of a packed
struct field when it can lead to an "unaligned" address.  Clang
doesn't support this warning.

This triggers the following errors (-Werror) when building three
particular BPF selftests with GCC:

  progs/test_cls_redirect.c
  986 |         if (ipv4_is_fragment((void *)&encap->ip)) {
  progs/test_cls_redirect_dynptr.c
  410 |         pkt_ipv4_checksum((void *)&encap_gre->ip);
  progs/test_cls_redirect.c
  521 |         pkt_ipv4_checksum((void *)&encap_gre->ip);
  progs/test_tc_tunnel.c
   232 |         set_ipv4_csum((void *)&h_outer.ip);

These warnings do not signal any real problem in the tests as far as I
can see.

This patch adds pragmas to these test files that inhibit the
-Waddress-of-packed-member if the compiler is not Clang.

Tested in bpf-next master.
No regressions.

Signed-off-by: Jose E. Marchesi <jose.marchesi@xxxxxxxxxx>
Cc: Andrii Nakryiko <andrii.nakryiko@xxxxxxxxx>
Cc: Yonghong Song <yhs@xxxxxxxx>
Cc: Eduard Zingerman <eddyz87@xxxxxxxxx>
Cc: David Faust <david.faust@xxxxxxxxxx>
Cc: Cupertino Miranda <cupertino.miranda@xxxxxxxxxx>
---
 tools/testing/selftests/bpf/progs/test_cls_redirect.c        | 4 ++++
 tools/testing/selftests/bpf/progs/test_cls_redirect_dynptr.c | 4 ++++
 tools/testing/selftests/bpf/progs/test_tc_tunnel.c           | 4 ++++
 3 files changed, 12 insertions(+)

diff --git a/tools/testing/selftests/bpf/progs/test_cls_redirect.c b/tools/testing/selftests/bpf/progs/test_cls_redirect.c
index 66b304982245..23e950ad84d2 100644
--- a/tools/testing/selftests/bpf/progs/test_cls_redirect.c
+++ b/tools/testing/selftests/bpf/progs/test_cls_redirect.c
@@ -22,6 +22,10 @@
 
 #include "test_cls_redirect.h"
 
+#if !__clang__
+#pragma GCC diagnostic ignored "-Waddress-of-packed-member"
+#endif
+
 #ifdef SUBPROGS
 #define INLINING __noinline
 #else
diff --git a/tools/testing/selftests/bpf/progs/test_cls_redirect_dynptr.c b/tools/testing/selftests/bpf/progs/test_cls_redirect_dynptr.c
index f41c81212ee9..af280e197c55 100644
--- a/tools/testing/selftests/bpf/progs/test_cls_redirect_dynptr.c
+++ b/tools/testing/selftests/bpf/progs/test_cls_redirect_dynptr.c
@@ -23,6 +23,10 @@
 #include "test_cls_redirect.h"
 #include "bpf_kfuncs.h"
 
+#if !__clang__
+#pragma GCC diagnostic ignored "-Waddress-of-packed-member"
+#endif
+
 #define offsetofend(TYPE, MEMBER) \
 	(offsetof(TYPE, MEMBER) + sizeof((((TYPE *)0)->MEMBER)))
 
diff --git a/tools/testing/selftests/bpf/progs/test_tc_tunnel.c b/tools/testing/selftests/bpf/progs/test_tc_tunnel.c
index e6e678aa9874..d3e439ff323b 100644
--- a/tools/testing/selftests/bpf/progs/test_tc_tunnel.c
+++ b/tools/testing/selftests/bpf/progs/test_tc_tunnel.c
@@ -20,6 +20,10 @@
 #include <bpf/bpf_endian.h>
 #include <bpf/bpf_helpers.h>
 
+#if !__clang__
+#pragma GCC diagnostic ignored "-Waddress-of-packed-member"
+#endif
+
 static const int cfg_port = 8000;
 
 static const int cfg_udp_src = 20000;
-- 
2.30.2