libbpf-tools: Fix misaligned pointer accesses in drsnoop

The perf buffer in drsnoop doesn't maintain 8 byte alignment
for delta_ns, nr_reclaimed and nr_free_pages in struct event.
When building with "-fsanitize=alignment -fsanitize-trap=undefined"
failures happen in handle_event. Fix these by copying the event
from the perf buffer before accessing.

This is similar to a fix in exitsnoop where different ways to handle
misaligned pointers were discussed:
iovisor#4760

Signed-off-by: Ian Rogers <[email protected]>

libbpf-tools/drsnoop.c

@@ -118,19 +118,26 @@ static void sig_int(int signo)
 
 void handle_event(void *ctx, int cpu, void *data, __u32 data_sz)
 {
- const struct event *e = data;
+ struct event e;
  struct tm *tm;
  char ts[32];
  time_t t;
 
+ if (data_sz < sizeof(e)) {
+ printf("Error: packet too small\n");
+ return;
+ }
+ /* Copy data as alignment in the perf buffer isn't guaranteed. */
+ memcpy(&e, data, sizeof(e));
+
  time(&t);
  tm = localtime(&t);
  strftime(ts, sizeof(ts), "%H:%M:%S", tm);
  printf("%-8s %-16s %-6d %8.3f %5lld",
- ts, e->task, e->pid, e->delta_ns / 1000000.0,
- e->nr_reclaimed);
+ ts, e.task, e.pid, e.delta_ns / 1000000.0,
+ e.nr_reclaimed);
  if (env.extended)
- printf(" %8llu", e->nr_free_pages * page_size / 1024);
+ printf(" %8llu", e.nr_free_pages * page_size / 1024);
  printf("\n");
 }