Bcc build fixes for Android (#2142)

* Mark unused parameters as unused

In Android, we are building libbpf with -Wunused-parameter, mark the
parameters in bpf_detach_tracepoint to prevent errors.

Change-Id: I2d0011746af80898e55d456b973a95330ce6be71
Signed-off-by: Joel Fernandes <joel@joelfernandes.org>

* Avoid void pointer arithmetic

In Android, we build libbpf with -Wpointer-arith, this causes warnings
as below. Avoid void pointer arithmetic to prevent the warning.

external/bcc/src/cc/perf_reader.c:189:26: error: arithmetic on a pointer
to void is a GNU extension [-Werror,-Wpointer-arith] memcpy(reader->buf
+ len, base, e->size - len);                               ~~~~~~~~~~~ ^

Change-Id: If06535459473c78799b38119786a91e74a208895
Signed-off-by: Joel Fernandes <joel@joelfernandes.org>

* Cast correctly for unsigned long format specifier

In Android, -Wformat gets passed to the compiler causing a warning. Fix
it by casting.

external/bcc/src/cc/libbpf.c:972:58: error: format specifies type
'unsigned long' but the argument has type 'uint64_t' (aka 'unsigned lo
ng long') [-Werror,-Wformat]

Change-Id: I5e70eeff983f20a0b921e81aee7ddbee6d7de2b3
Signed-off-by: Joel Fernandes <joel@joelfernandes.org>

src/cc/libbpf.c

@@ -84,6 +84,8 @@
 
 #define min(x, y) ((x) < (y) ? (x) : (y))
 
+#define UNUSED(expr) do { (void)(expr); } while (0)
+
 struct bpf_helper {
   char *name;
   char *required_version;
@@ -979,7 +981,7 @@ int bpf_attach_uprobe(int progfd, enum bpf_probe_attach_type attach_type,
       goto error;
     }
     res = snprintf(buf, sizeof(buf), "%c:%ss/%s %s:0x%lx", attach_type==BPF_PROBE_ENTRY ? 'p' : 'r',
-                   event_type, event_alias, binary_path, offset);
+                   event_type, event_alias, binary_path, (unsigned long)offset);
     if (res < 0 || res >= sizeof(buf)) {
       fprintf(stderr, "Event alias (%s) too long for buffer\n", event_alias);
       goto error;
@@ -1108,6 +1110,8 @@ int bpf_attach_tracepoint(int progfd, const char *tp_category,
 }
 
 int bpf_detach_tracepoint(const char *tp_category, const char *tp_name) {
+  UNUSED(tp_category);
+  UNUSED(tp_name);
   // Right now, there is nothing to do, but it's a good idea to encourage
   // callers to detach anything they attach.
   return 0;

src/cc/perf_reader.c

@@ -186,7 +186,7 @@ void perf_reader_event_read(struct perf_reader *reader) {
       reader->buf = realloc(reader->buf, e->size);
       size_t len = sentinel - begin;
       memcpy(reader->buf, begin, len);
-      memcpy(reader->buf + len, base, e->size - len);
+      memcpy((void *)((unsigned long)reader->buf + len), base, e->size - len);
       ptr = reader->buf;
     }