bpf, tests: Add test for 32-bit context pointer argument passing

On a 32-bit architecture, the context pointer will occupy the low
half of R1, and the other half will be zero.
Signed-off-by: Johan Almbladh <johan.almbladh@anyfinetworks.com>
Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>
Link: https://lore.kernel.org/bpf/20210809091829.810076-12-johan.almbladh@anyfinetworks.com

lib/test_bpf.c

@@ -2092,6 +2092,22 @@ static struct bpf_test tests[] = {
 #undef NUMER
 #undef DENOM
 	},
+#ifdef CONFIG_32BIT
+	{
+		"INT: 32-bit context pointer word order and zero-extension",
+		.u.insns_int = {
+			BPF_ALU32_IMM(BPF_MOV, R0, 0),
+			BPF_JMP32_IMM(BPF_JEQ, R1, 0, 3),
+			BPF_ALU64_IMM(BPF_RSH, R1, 32),
+			BPF_JMP32_IMM(BPF_JNE, R1, 0, 1),
+			BPF_ALU32_IMM(BPF_MOV, R0, 1),
+			BPF_EXIT_INSN(),
+		},
+		INTERNAL,
+		{ },
+		{ { 0, 1 } }
+	},
+#endif
 	{
 		"check: missing ret",
 		.u.insns = {