bpf: add various verifier test cases

This patch adds various verifier test cases:

1) A test case for the pruning issue when tracking alignment
   is used.
2) Various PTR_TO_MAP_VALUE_OR_NULL tests to make sure pointer
   arithmetic turns such register into UNKNOWN_VALUE type.
3) Test cases for the special treatment of LD_ABS/LD_IND to
   make sure verifier doesn't break calling convention here.
   Latter is needed, since f.e. arm64 JIT uses r1 - r5 for
   storing temporary data, so they really must be marked as
   NOT_INIT.

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

tools/include/linux/filter.h

@@ -208,6 +208,16 @@
 		.off   = OFF,					\
 		.imm   = IMM })
 
+/* Unconditional jumps, goto pc + off16 */
+
+#define BPF_JMP_A(OFF)						\
+	((struct bpf_insn) {					\
+		.code  = BPF_JMP | BPF_JA,			\
+		.dst_reg = 0,					\
+		.src_reg = 0,					\
+		.off   = OFF,					\
+		.imm   = 0 })
+
 /* Function call */
 
 #define BPF_EMIT_CALL(FUNC)					\