On 1/31/24 1:44 AM, Jose E. Marchesi wrote:
[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.
Look like this is not true.
$ cat t.c
struct __attribute__ ((packed)) Packed {
char a;
int b;
int c;
char d;
};
void test(const int *i, int *ptr);
int foo() {
struct Packed p;
p.c = 1;
test(&p.c, &p.c);
return 0;
}
$ /home/yhs/work/llvm-project/llvm/build.16/install/bin/clang --version
clang version 16.0.3 (https://github.com/llvm/llvm-project.git da3cd333bea572fb10470f610a27f22bcb84b08c)
Target: x86_64-unknown-linux-gnu
Thread model: posix
InstalledDir: /home/yhs/work/llvm-project/llvm/build.16/install/bin
$ /home/yhs/work/llvm-project/llvm/build.16/install/bin/clang --target=bpf -O2 -c t.c
t.c:12:9: warning: taking address of packed member 'c' of class or structure 'Packed' may result in an unaligned pointer value [-Waddress-of-packed-member]
test(&p.c, &p.c);
^~~
t.c:12:15: warning: taking address of packed member 'c' of class or structure 'Packed' may result in an unaligned pointer value [-Waddress-of-packed-member]
test(&p.c, &p.c);
^~~
2 warnings generated.
$ /home/yhs/work/llvm-project/llvm/build.16/install/bin/clang --target=bpf -O2 -c t.c -Wno-address-of-packed-member
$
But each compiler internal diag detection logic could be different, so
it is totally possible that gcc might emit warning while clang does not
like in some selftests mentioned.
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
So I suggest to remove the above '#if !__clang__' guard.
+
#ifdef SUBPROGS
#define INLINING __noinline
#else
[...]
