bpf, tests: Add load store test case for tail call

Add test case to enusre that the caller and callee's fp offsets are
correct during tail call (mainly asserting for arm64 JIT).

Tested on both big-endian and little-endian arm64 qemu, result:

 test_bpf: Summary: 1026 PASSED, 0 FAILED, [1014/1014 JIT'ed]
 test_bpf: test_tail_calls: Summary: 10 PASSED, 0 FAILED, [10/10 JIT'ed]
 test_bpf: test_skb_segment: Summary: 2 PASSED, 0 FAILED

Signed-off-by: Xu Kuohai <xukuohai@huawei.com>
Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>
Link: https://lore.kernel.org/bpf/20220321152852.2334294-6-xukuohai@huawei.com

Author: Xu Kuohai

lib/test_bpf.c

@@ -14950,6 +14950,36 @@ static struct tail_call_test tail_call_tests[] = {
 		},
 		.result = 10,
 	},
+	{
+		"Tail call load/store leaf",
+		.insns = {
+			BPF_ALU64_IMM(BPF_MOV, R1, 1),
+			BPF_ALU64_IMM(BPF_MOV, R2, 2),
+			BPF_ALU64_REG(BPF_MOV, R3, BPF_REG_FP),
+			BPF_STX_MEM(BPF_DW, R3, R1, -8),
+			BPF_STX_MEM(BPF_DW, R3, R2, -16),
+			BPF_LDX_MEM(BPF_DW, R0, BPF_REG_FP, -8),
+			BPF_JMP_REG(BPF_JNE, R0, R1, 3),
+			BPF_LDX_MEM(BPF_DW, R0, BPF_REG_FP, -16),
+			BPF_JMP_REG(BPF_JNE, R0, R2, 1),
+			BPF_ALU64_IMM(BPF_MOV, R0, 0),
+			BPF_EXIT_INSN(),
+		},
+		.result = 0,
+		.stack_depth = 32,
+	},
+	{
+		"Tail call load/store",
+		.insns = {
+			BPF_ALU64_IMM(BPF_MOV, R0, 3),
+			BPF_STX_MEM(BPF_DW, BPF_REG_FP, R0, -8),
+			TAIL_CALL(-1),
+			BPF_ALU64_IMM(BPF_MOV, R0, -1),
+			BPF_EXIT_INSN(),
+		},
+		.result = 0,
+		.stack_depth = 16,
+	},
 	{
 		"Tail call error path, max count reached",
 		.insns = {