bpf: provide a generic macro for percpu values for selftests

To overcome bugs as described and fixed in 89087c456fb5 ("bpf: Fix
values type used in test_maps"), provide a generic BPF_DECLARE_PERCPU()
and bpf_percpu() accessor macro for all percpu map values used in
tests.

Declaring variables works as follows (also works for structs):

  BPF_DECLARE_PERCPU(uint32_t, my_value);

They can then be accessed normally as uint32_t type through:

  bpf_percpu(my_value, <cpu_nr>)

For example:

  bpf_percpu(my_value, 0)++;

Implicitly, we make sure that the passed type is allocated and aligned
by gcc at least on a 8-byte boundary, so that it works together with
the map lookup/update syscall for percpu maps. We use it as a usage
example in test_maps, so that others are free to adapt this into their
code when necessary.

Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>
Acked-by: Alexei Starovoitov <ast@kernel.org>
Signed-off-by: David S. Miller <davem@davemloft.net>

1 files changed, 7 insertions, 0 deletions

diff --git a/tools/testing/selftests/bpf/bpf_util.h b/tools/testing/selftests/bpf/bpf_util.h
index 7de27966103d..369e7d7bba80 100644
--- a/tools/testing/selftests/bpf/bpf_util.h
+++ b/tools/testing/selftests/bpf/bpf_util.h
@@ -54,4 +54,11 @@ static inline unsigned int bpf_num_possible_cpus(void)
 	return possible_cpus;
 }
 
+#define __bpf_percpu_val_align	__attribute__((__aligned__(8)))
+
+#define BPF_DECLARE_PERCPU(type, name)				\
+	struct { type v; /* padding */ } __bpf_percpu_val_align	\
+		name[bpf_num_possible_cpus()]
+#define bpf_percpu(name, cpu) name[(cpu)].v
+
 #endif /* __BPF_UTIL__ */