bpf: Change syscall_nr type to int in struct syscall_tp_t

linux-rt-devel tree contains a patch (b1773eac3f29c ("sched: Add support
for lazy preemption")) that adds an extra member to struct trace_entry.
This causes the offset of args field in struct trace_event_raw_sys_enter
be different from the one in struct syscall_trace_enter:

struct trace_event_raw_sys_enter {
struct trace_entry ent; /* 0 12 */

/* XXX last struct has 3 bytes of padding */
/* XXX 4 bytes hole, try to pack */

long int id; /* 16 8 */
long unsigned int args[6]; /* 24 48 */
/* --- cacheline 1 boundary (64 bytes) was 8 bytes ago --- */
char __data[]; /* 72 0 */

/* size: 72, cachelines: 2, members: 4 */
/* sum members: 68, holes: 1, sum holes: 4 */
/* paddings: 1, sum paddings: 3 */
/* last cacheline: 8 bytes */
};

struct syscall_trace_enter {
struct trace_entry ent; /* 0 12 */

/* XXX last struct has 3 bytes of padding */

int nr; /* 12 4 */
long unsigned int args[]; /* 16 0 */

/* size: 16, cachelines: 1, members: 3 */
/* paddings: 1, sum paddings: 3 */
/* last cacheline: 16 bytes */
};

This, in turn, causes perf_event_set_bpf_prog() fail while running bpf
test_profiler testcase because max_ctx_offset is calculated based on the
former struct, while off on the latter:

10488 if (is_tracepoint || is_syscall_tp) {
10489 int off = trace_event_get_offsets(event->tp_event);
10490
10491 if (prog->aux->max_ctx_offset > off)
10492 return -EACCES;
10493 }

What bpf program is actually getting is a pointer to struct
syscall_tp_t, defined in kernel/trace/trace_syscalls.c. This patch fixes
the problem by aligning struct syscall_tp_t with struct
syscall_trace_(enter|exit) and changing the tests to use these structs
to dereference context.

Signed-off-by: Artem Savkov <[e-mail]>
Signed-off-by: Andrii Nakryiko <[e-mail]>
Acked-by: Steven Rostedt (Google) <[e-mail]>
Link: https://lore.kernel.org/bpf/[e-mail]

kernel/trace/trace_syscalls.c

···
 {
 	struct syscall_tp_t {
 		struct trace_entry ent;
-		unsigned long syscall_nr;
+		int syscall_nr;
 		unsigned long args[SYSCALL_DEFINE_MAXARGS];
 	} __aligned(8) param;
 	int i;
···
 {
 	struct syscall_tp_t {
 		struct trace_entry ent;
-		unsigned long syscall_nr;
+		int syscall_nr;
 		unsigned long ret;
 	} __aligned(8) param;
 

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

···
 }
 
 SEC("tracepoint/syscalls/sys_enter_kill")
-int tracepoint__syscalls__sys_enter_kill(struct trace_event_raw_sys_enter* ctx)
+int tracepoint__syscalls__sys_enter_kill(struct syscall_trace_enter* ctx)
 {
 	struct bpf_func_stats_ctx stats_ctx;
 

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

···
 bool fentry_called = false;
 
 SEC("tp/syscalls/sys_enter_nanosleep")
-int handle__tp(struct trace_event_raw_sys_enter *args)
+int handle__tp(struct syscall_trace_enter *args)
 {
 	struct __kernel_timespec *ts;
 	long tv_nsec;
 
-	if (args->id != __NR_nanosleep)
+	if (args->nr != __NR_nanosleep)
 		return 0;
 
 	ts = (void *)args->args[0];