selftests/bpf: Fix a few tests for GCC related warnings.

selftests/bpf: Fix a few tests for GCC related warnings.

This patch corrects a few warnings to allow selftests to compile for
GCC.

-- progs/cpumask_failure.c --

progs/bpf_misc.h:136:22: error: ‘cpumask’ is used uninitialized
[-Werror=uninitialized]
  136 | #define __sink(expr) asm volatile("" : "+g"(expr))
      |                      ^~~
progs/cpumask_failure.c:68:9: note: in expansion of macro ‘__sink’
   68 |         __sink(cpumask);

The macro __sink(cpumask) with the '+' contraint modifier forces the
the compiler to expect a read and write from cpumask. GCC detects
that cpumask is never initialized and reports an error.
This patch removes the spurious non required definitions of cpumask.

-- progs/dynptr_fail.c --

progs/dynptr_fail.c:1444:9: error: ‘ptr1’ may be used uninitialized
[-Werror=maybe-uninitialized]
 1444 |         bpf_dynptr_clone(&ptr1, &ptr2);

Many of the tests in the file are related to the detection of
uninitialized pointers by the verifier. GCC is able to detect possible
uninitialized values, and reports this as an error.
The patch initializes all of the previous uninitialized structs.

-- progs/test_tunnel_kern.c --

progs/test_tunnel_kern.c:590:9: error: array subscript 1 is outside
array bounds of ‘struct geneve_opt[1]’ [-Werror=array-bounds=]
  590 |         *(int *) &gopt.opt_data = bpf_htonl(0xdeadbeef);
      |         ^~~~~~~~~~~~~~~~~~~~~~~
progs/test_tunnel_kern.c:575:27: note: at offset 4 into object ‘gopt’ of
size 4
  575 |         struct geneve_opt gopt;

This tests accesses beyond the defined data for the struct geneve_opt
which contains as last field "u8 opt_data[0]" which clearly does not get
reserved space (in stack) in the function header. This pattern is
repeated in ip6geneve_set_tunnel and geneve_set_tunnel functions.
GCC is able to see this and emits a warning.
The patch introduces a local struct that allocates enough space to
safely allow the write to opt_data field.

-- progs/jeq_infer_not_null_fail.c --

progs/jeq_infer_not_null_fail.c:21:40: error: array subscript ‘struct
bpf_map[0]’ is partly outside array bounds of ‘struct <anonymous>[1]’
[-Werror=array-bounds=]
   21 |         struct bpf_map *inner_map = map->inner_map_meta;
      |                                        ^~
progs/jeq_infer_not_null_fail.c:14:3: note: object ‘m_hash’ of size 32
   14 | } m_hash SEC(".maps");

This example defines m_hash in the context of the compilation unit and
casts it to struct bpf_map which is much smaller than the size of struct
bpf_map. It errors out in GCC when it attempts to access an element that
would be defined in struct bpf_map outsize of the defined limits for
m_hash.
This patch disables the warning through a GCC pragma.

This changes were tested in bpf-next master selftests without any
regressions.

Signed-off-by: Cupertino Miranda <cupertino.miranda@oracle.com>
Cc: jose.marchesi@oracle.com
Cc: david.faust@oracle.com
Cc: Yonghong Song <yonghong.song@linux.dev>
Cc: Eduard Zingerman <eddyz87@gmail.com>
Cc: Andrii Nakryiko <andrii.nakryiko@gmail.com>
Link: https://lore.kernel.org/r/20240510183850.286661-2-cupertino.miranda@oracle.com
Signed-off-by: Alexei Starovoitov <ast@kernel.org>