selftests/bpf: Attempt to build BPF programs with -Wsign-compare

GCC's -Wall includes -Wsign-compare while clang does not.
Since BPF programs are built with clang we need to add this flag explicitly
to catch problematic comparisons like:

int i = -1;
unsigned int j = 1;
if (i < j) // this is false.

long i = -1;
unsigned int j = 1;
if (i < j) // this is true.

C standard for reference:

- If either operand is unsigned long the other shall be converted to unsigned long.

- Otherwise, if one operand is a long int and the other unsigned int, then if a
long int can represent all the values of an unsigned int, the unsigned int
shall be converted to a long int; otherwise both operands shall be converted to
unsigned long int.

- Otherwise, if either operand is long, the other shall be converted to long.

- Otherwise, if either operand is unsigned, the other shall be converted to unsigned.

Unfortunately clang's -Wsign-compare is very noisy.
It complains about (s32)a == (u32)b which is safe and doen't have surprising behavior.

This patch fixes some of the issues. It needs a follow up to fix the rest.

Signed-off-by: Alexei Starovoitov <[e-mail]>
Signed-off-by: Andrii Nakryiko <[e-mail]>
Acked-by: Jiri Olsa <[e-mail]>
Acked-by: Kumar Kartikeya Dwivedi <[e-mail]>
Link: https://lore.kernel.org/bpf/[e-mail]

tools/testing/selftests/bpf/Makefile

···
 BPF_CFLAGS = -g -Wall -Werror -D__TARGET_ARCH_$(SRCARCH) $(MENDIAN)	\
 	     -I$(INCLUDE_DIR) -I$(CURDIR) -I$(APIDIR)			\
 	     -I$(abspath $(OUTPUT)/../usr/include)
+# TODO: enable me -Wsign-compare
 
 CLANG_CFLAGS = $(CLANG_SYS_INCLUDES) \
 	       -Wno-compare-distinct-pointer-types

tools/testing/selftests/bpf/progs/bpf_iter_bpf_percpu_hash_map.c

···
 } hashmap1 SEC(".maps");
 
 /* will set before prog run */
-volatile const __u32 num_cpus = 0;
+volatile const __s32 num_cpus = 0;
 
 /* will collect results during prog run */
 __u32 key_sum_a = 0, key_sum_b = 0, key_sum_c = 0;

tools/testing/selftests/bpf/progs/bpf_iter_task_vmas.c

···
 		return 0;
 
 	file = vma->vm_file;
-	if (task->tgid != pid) {
+	if (task->tgid != (pid_t)pid) {
 		if (one_task)
 			one_task_error = 1;
 		return 0;

tools/testing/selftests/bpf/progs/bpf_iter_tasks.c

···
 		return 0;
 	}
 
-	if (task->pid != tid)
+	if (task->pid != (pid_t)tid)
 		num_unknown_tid++;
 	else
 		num_known_tid++;

tools/testing/selftests/bpf/progs/bpf_iter_test_kern4.c

···
 	}
 
 	/* fill seq_file buffer */
-	for (i = 0; i < print_len; i++)
+	for (i = 0; i < (int)print_len; i++)
 		bpf_seq_write(seq, &seq_num, sizeof(seq_num));
 
 	return ret;

tools/testing/selftests/bpf/progs/cgroup_getset_retval_setsockopt.c

···
 __u32 invocations = 0;
 __u32 assertion_error = 0;
 __u32 retval_value = 0;
-__u32 page_size = 0;
+__s32 page_size = 0;
 
 SEC("cgroup/setsockopt")
 int get_retval(struct bpf_sockopt *ctx)

tools/testing/selftests/bpf/progs/cgrp_ls_sleepable.c

···
 	__type(value, long);
 } map_a SEC(".maps");
 
-__u32 target_pid;
+__s32 target_pid;
 __u64 cgroup_id;
 int target_hid;
 bool is_cgroup1;

tools/testing/selftests/bpf/progs/cpumask_success.c

···
 int BPF_PROG(test_copy_any_anyand, struct task_struct *task, u64 clone_flags)
 {
 	struct bpf_cpumask *mask1, *mask2, *dst1, *dst2;
-	u32 cpu;
+	int cpu;
 
 	if (!is_test_task())
 		return 0;

tools/testing/selftests/bpf/progs/iters.c

···
 #include <bpf/bpf_helpers.h>
 #include "bpf_misc.h"
 
-#define ARRAY_SIZE(x) (sizeof(x) / sizeof((x)[0]))
+#define ARRAY_SIZE(x) (int)(sizeof(x) / sizeof((x)[0]))
 
 static volatile int zero = 0;
 
···
 
 	while ((t = bpf_iter_num_next(it))) {
 		i = *t;
-		if (i >= n)
+		if ((__u32)i >= n)
 			break;
 		sum += arr[i];
 	}

tools/testing/selftests/bpf/progs/linked_funcs1.c

···
 #include "bpf_misc.h"
 
 /* weak and shared between two files */
-const volatile int my_tid __weak;
+const volatile __u32 my_tid __weak;
 long syscall_id __weak;
 
 int output_val1;

tools/testing/selftests/bpf/progs/linked_funcs2.c

···
 {
 	static volatile int whatever;
 
-	if (my_tid != (u32)bpf_get_current_pid_tgid() || id != syscall_id)
+	if (my_tid != (s32)bpf_get_current_pid_tgid() || id != syscall_id)
 		return 0;
 
 	/* make sure we have CO-RE relocations in main program */

tools/testing/selftests/bpf/progs/linked_list.c

···
 #include "bpf_experimental.h"
 
 #ifndef ARRAY_SIZE
-#define ARRAY_SIZE(x) (sizeof(x) / sizeof((x)[0]))
+#define ARRAY_SIZE(x) (int)(sizeof(x) / sizeof((x)[0]))
 #endif
 
 #include "linked_list.h"

tools/testing/selftests/bpf/progs/local_storage.c

···
 
 #define DUMMY_STORAGE_VALUE 0xdeadbeef
 
-int monitored_pid = 0;
+__u32 monitored_pid = 0;
 int inode_storage_result = -1;
 int sk_storage_result = -1;
 int task_storage_result = -1;

tools/testing/selftests/bpf/progs/lsm.c

···
 	if (ret != 0)
 		return ret;
 
-	__u32 pid = bpf_get_current_pid_tgid() >> 32;
+	__s32 pid = bpf_get_current_pid_tgid() >> 32;
 	int is_stack = 0;
 
 	is_stack = (vma->vm_start <= vma->vm_mm->start_stack &&

tools/testing/selftests/bpf/progs/normal_map_btf.c

···
 	struct node_data *new;
 	int zero = 0;
 
-	if (done || (u32)bpf_get_current_pid_tgid() != pid)
+	if (done || (int)bpf_get_current_pid_tgid() != pid)
 		return 0;
 
 	value = bpf_map_lookup_elem(&array, &zero);

tools/testing/selftests/bpf/progs/profiler.inc.h

···
 } disallowed_exec_inodes SEC(".maps");
 
 #ifndef ARRAY_SIZE
-#define ARRAY_SIZE(arr) (sizeof(arr) / sizeof(arr[0]))
+#define ARRAY_SIZE(arr) (int)(sizeof(arr) / sizeof(arr[0]))
 #endif
 
 static INLINE bool IS_ERR(const void* ptr)
···
 	for (int i = 0; i < ARRAY_SIZE(arr_struct->array); i++) {
 		struct var_kill_data_t* past_kill_data = &arr_struct->array[i];
 
-		if (past_kill_data != NULL && past_kill_data->kill_target_pid == tpid) {
+		if (past_kill_data != NULL && past_kill_data->kill_target_pid == (pid_t)tpid) {
 			bpf_probe_read_kernel(kill_data, sizeof(*past_kill_data),
 					      past_kill_data);
 			void* payload = kill_data->payload;

tools/testing/selftests/bpf/progs/sockopt_inherit.c

···
 #define CUSTOM_INHERIT2			1
 #define CUSTOM_LISTENER			2
 
-__u32 page_size = 0;
+__s32 page_size = 0;
 
 struct sockopt_inherit {
 	__u8 val;

tools/testing/selftests/bpf/progs/sockopt_multi.c

···
 
 char _license[] SEC("license") = "GPL";
 
-__u32 page_size = 0;
+__s32 page_size = 0;
 
 SEC("cgroup/getsockopt")
 int _getsockopt_child(struct bpf_sockopt *ctx)

tools/testing/selftests/bpf/progs/sockopt_qos_to_cc.c

···
 
 char _license[] SEC("license") = "GPL";
 
-__u32 page_size = 0;
+__s32 page_size = 0;
 
 SEC("cgroup/setsockopt")
 int sockopt_qos_to_cc(struct bpf_sockopt *ctx)

tools/testing/selftests/bpf/progs/test_bpf_ma.c

···
 const volatile unsigned int data_btf_ids[ARRAY_SIZE(data_sizes)] = {};
 
 int err = 0;
-int pid = 0;
+u32 pid = 0;
 
 #define DEFINE_ARRAY_WITH_KPTR(_size) \
 	struct bin_data_##_size { \

tools/testing/selftests/bpf/progs/test_core_reloc_kernel.c

···
 	struct task_struct *task = (void *)bpf_get_current_task();
 	struct core_reloc_kernel_output *out = (void *)&data.out;
 	uint64_t pid_tgid = bpf_get_current_pid_tgid();
-	uint32_t real_tgid = (uint32_t)pid_tgid;
+	int32_t real_tgid = (int32_t)pid_tgid;
 	int pid, tgid;
 
 	if (data.my_pid_tgid != pid_tgid)

tools/testing/selftests/bpf/progs/test_core_reloc_module.c

···
 #if __has_builtin(__builtin_preserve_enum_value)
 	struct core_reloc_module_output *out = (void *)&data.out;
 	__u64 pid_tgid = bpf_get_current_pid_tgid();
-	__u32 real_tgid = (__u32)(pid_tgid >> 32);
-	__u32 real_pid = (__u32)pid_tgid;
+	__s32 real_tgid = (__s32)(pid_tgid >> 32);
+	__s32 real_pid = (__s32)pid_tgid;
 
 	if (data.my_pid_tgid != pid_tgid)
 		return 0;
···
 #if __has_builtin(__builtin_preserve_enum_value)
 	struct core_reloc_module_output *out = (void *)&data.out;
 	__u64 pid_tgid = bpf_get_current_pid_tgid();
-	__u32 real_tgid = (__u32)(pid_tgid >> 32);
-	__u32 real_pid = (__u32)pid_tgid;
+	__s32 real_tgid = (__s32)(pid_tgid >> 32);
+	__s32 real_pid = (__s32)pid_tgid;
 
 	if (data.my_pid_tgid != pid_tgid)
 		return 0;

tools/testing/selftests/bpf/progs/test_fsverity.c

···
 		return 0;
 	got_fsverity = 1;
 
-	for (i = 0; i < sizeof(digest); i++) {
+	for (i = 0; i < (int)sizeof(digest); i++) {
 		if (digest[i] != expected_digest[i])
 			return 0;
 	}

tools/testing/selftests/bpf/progs/test_skc_to_unix_sock.c

···
 	len = unix_sk->addr->len - sizeof(short);
 	path[0] = '@';
 	for (i = 1; i < len; i++) {
-		if (i >= sizeof(struct sockaddr_un))
+		if (i >= (int)sizeof(struct sockaddr_un))
 			break;
 
 		path[i] = unix_sk->addr->name->sun_path[i];

tools/testing/selftests/bpf/progs/test_xdp_do_redirect.c

···
 	if (payload + 1 > data_end)
 		return XDP_ABORTED;
 
-	if (xdp->ingress_ifindex != ifindex_in)
+	if (xdp->ingress_ifindex != (__u32)ifindex_in)
 		return XDP_ABORTED;
 
 	if (metadata + 1 > data)