On 5/7/24 11:20 AM, Jose E. Marchesi wrote:
On 5/7/24 7:05 AM, Jose E. Marchesi wrote:
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.
Interesting. The error message is 'maybe uninitialized' but not
an error to complain out-of-bound access. But anyway, since gcc
produces a warning, your patch silences it and LGTM.
Acked-by: Yonghong Song <yonghong.song@xxxxxxxxx>
Please hold on. The right warning to inhibit is -Wmaybe-uninitialized,
which is GCC specific.
So it must be:
#if !defined(__clang__)
#pragma GCC diagnostic ignored "-Wmaybe-uninitialized"
#endif
Unless you disagree I am testing this and will send a V2 with your
Acked-by.
I thought -Wmaybe-unitialized also available to clang but just checked
that clang does not have this. So your above change looks good to me.
Sorry about this. I hate to be erratic, but so many small patches
today.
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@xxxxxxxxxx>
Cc: david.faust@xxxxxxxxxx
Cc: cupertino.miranda@xxxxxxxxxx
Cc: Yonghong Song <yonghong.song@xxxxxxxxx>
Cc: Eduard Zingerman <eddyz87@xxxxxxxxx>
---
tools/testing/selftests/bpf/progs/verifier_global_subprogs.c | 5 +++++
1 file changed, 5 insertions(+)
diff --git
a/tools/testing/selftests/bpf/progs/verifier_global_subprogs.c
b/tools/testing/selftests/bpf/progs/verifier_global_subprogs.c
index baff5ffe9405..d05dc218b7e9 100644
--- a/tools/testing/selftests/bpf/progs/verifier_global_subprogs.c
+++ b/tools/testing/selftests/bpf/progs/verifier_global_subprogs.c
@@ -8,6 +8,11 @@
#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. */
+#pragma GCC diagnostic ignored "-Wuninitialized"
+
int arr[1];
int unkn_idx;
const volatile bool call_dead_subprog = false;
