From: "Jose E. Marchesi" jose.marchesi@oracle.com
[ Upstream commit cd3fc3b9782130a5bc1dc3dfccffbc1657637a93 ]
[Changes from V1: - The warning to disable is -Wmaybe-uninitialized, not -Wuninitialized. - This warning is only supported in GCC.]
The BPF selftest verifier_global_subprogs.c contains code that purposedly performs out of bounds access to memory, to check whether the kernel verifier is able to catch them. For example:
__noinline int global_unsupp(const int *mem) { if (!mem) return 0; return mem[100]; /* BOOM */ }
With -O1 and higher and no inlining, GCC notices this fact and emits a "maybe uninitialized" warning. This is by design. Note that the emission of these warnings is highly dependent on the precise optimizations that are performed.
This patch adds a compiler pragma to verifier_global_subprogs.c to ignore these warnings.
Tested in bpf-next master. No regressions.
Signed-off-by: Jose E. Marchesi jose.marchesi@oracle.com Cc: david.faust@oracle.com Cc: cupertino.miranda@oracle.com Cc: Yonghong Song yonghong.song@linux.dev Cc: Eduard Zingerman eddyz87@gmail.com Acked-by: Yonghong Song yonghong.song@linux.dev Link: https://lore.kernel.org/r/20240507184756.1772-1-jose.marchesi@oracle.com Signed-off-by: Alexei Starovoitov ast@kernel.org Signed-off-by: Sasha Levin sashal@kernel.org --- .../testing/selftests/bpf/progs/verifier_global_subprogs.c | 7 +++++++ 1 file changed, 7 insertions(+)
diff --git a/tools/testing/selftests/bpf/progs/verifier_global_subprogs.c b/tools/testing/selftests/bpf/progs/verifier_global_subprogs.c index baff5ffe94051..a9fc30ed4d732 100644 --- a/tools/testing/selftests/bpf/progs/verifier_global_subprogs.c +++ b/tools/testing/selftests/bpf/progs/verifier_global_subprogs.c @@ -8,6 +8,13 @@ #include "xdp_metadata.h" #include "bpf_kfuncs.h"
+/* The compiler may be able to detect the access to uninitialized + memory in the routines performing out of bound memory accesses and + emit warnings about it. This is the case of GCC. */ +#if !defined(__clang__) +#pragma GCC diagnostic ignored "-Wmaybe-uninitialized" +#endif + int arr[1]; int unkn_idx; const volatile bool call_dead_subprog = false;