bpf: avoid warning for wrong pointer cast

Two new functions in bpf contain a cast from a 'u64' to a
pointer. This works on 64-bit architectures but causes a warning
on all 32-bit architectures:

kernel/trace/bpf_trace.c: In function 'bpf_perf_event_output_tp':
kernel/trace/bpf_trace.c:350:13: error: cast to pointer from integer of different size [-Werror=int-to-pointer-cast]
  u64 ctx = *(long *)r1;

This changes the cast to first convert the u64 argument into a uintptr_t,
which is guaranteed to be the same size as a pointer.
Signed-off-by: Arnd Bergmann <arnd@arndb.de>
Fixes: 9940d67c ("bpf: support bpf_get_stackid() and bpf_perf_event_output() in tracepoint programs")
Acked-by: Alexei Starovoitov <ast@kernel.org>
Signed-off-by: David S. Miller <davem@davemloft.net>

kernel/trace/bpf_trace.c

@@ -351,7 +351,7 @@ static u64 bpf_perf_event_output_tp(u64 r1, u64 r2, u64 index, u64 r4, u64 size)
 	 * from bpf program and contain a pointer to 'struct pt_regs'. Fetch it
 	 * from there and call the same bpf_perf_event_output() helper
 	 */
-	u64 ctx = *(long *)r1;
+	u64 ctx = *(long *)(uintptr_t)r1;
 
 	return bpf_perf_event_output(ctx, r2, index, r4, size);
 }
@@ -369,7 +369,7 @@ static const struct bpf_func_proto bpf_perf_event_output_proto_tp = {
 
 static u64 bpf_get_stackid_tp(u64 r1, u64 r2, u64 r3, u64 r4, u64 r5)
 {
-	u64 ctx = *(long *)r1;
+	u64 ctx = *(long *)(uintptr_t)r1;
 
 	return bpf_get_stackid(ctx, r2, r3, r4, r5);
 }