Skip dereferences inside bpf_probe_reads calls (iovisor#1824)

* Skip all dereferences inside bpf_probe_read calls

If the user decides to rely on a manual call to bpf_probe_read, we
don't try to rewrite its last argument.  This is needed as the
rewriter starts to recognize and rewrite more and more dereferences.

* tools: fix dereferences following 1a765a1

src/cc/frontends/clang/b_frontend_action.cc

@@ -281,10 +281,7 @@ bool ProbeVisitor::VisitCallExpr(CallExpr *Call) {
  if (VarDecl *V = dyn_cast<VarDecl>(Call->getCalleeDecl())) {
  if (V->getName() == "bpf_probe_read" && Call->getNumArgs() >= 3) {
  const Expr *E = Call->getArg(2)->IgnoreParenCasts();
- if (const UnaryOperator *UnaryExpr = dyn_cast<UnaryOperator>(E)) {
- if (UnaryExpr->getOpcode() == UO_AddrOf)
- whitelist_.insert(E);
- }
+ whitelist_.insert(E);
  return true;
  }
  }

tools/biosnoop.py

@@ -94,8 +94,9 @@
  data.len = req->__data_len;
  data.sector = req->__sector;
  bpf_probe_read(&data.name, sizeof(data.name), valp->name);
+ struct gendisk *rq_disk = req->rq_disk;
  bpf_probe_read(&data.disk_name, sizeof(data.disk_name),
- req->rq_disk->disk_name);
+ rq_disk->disk_name);
  }
 
 /*

tools/filelife.py

@@ -84,14 +84,14 @@
  delta = (bpf_ktime_get_ns() - *tsp) / 1000000;
  birth.delete(&dentry);
 
- if (dentry->d_name.len == 0)
+ struct qstr d_name = dentry->d_name;
+ if (d_name.len == 0)
  return 0;
 
  if (bpf_get_current_comm(&data.comm, sizeof(data.comm)) == 0) {
  data.pid = pid;
  data.delta = delta;
- bpf_probe_read(&data.fname, sizeof(data.fname),
- (void *)dentry->d_name.name);
+ bpf_probe_read(&data.fname, sizeof(data.fname), d_name.name);
  }
 
  events.perf_submit(ctx, &data, sizeof(data));

tools/fileslower.py

@@ -111,8 +111,9 @@
  val.sz = count;
  val.ts = bpf_ktime_get_ns();
 
- val.name_len = de->d_name.len;
- bpf_probe_read(&val.name, sizeof(val.name), (void *)de->d_name.name);
+ struct qstr d_name = de->d_name;
+ val.name_len = d_name.len;
+ bpf_probe_read(&val.name, sizeof(val.name), d_name.name);
  bpf_get_current_comm(&val.comm, sizeof(val.comm));
  entryinfo.update(&pid, &val);
 

tools/filetop.py

@@ -100,14 +100,15 @@ def signal_ignore(signal, frame):
  // skip I/O lacking a filename
  struct dentry *de = file->f_path.dentry;
  int mode = file->f_inode->i_mode;
- if (de->d_name.len == 0 || TYPE_FILTER)
+ struct qstr d_name = de->d_name;
+ if (d_name.len == 0 || TYPE_FILTER)
  return 0;
 
  // store counts and sizes by pid & file
  struct info_t info = {.pid = pid};
  bpf_get_current_comm(&info.comm, sizeof(info.comm));
- info.name_len = de->d_name.len;
- bpf_probe_read(&info.name, sizeof(info.name), (void *)de->d_name.name);
+ info.name_len = d_name.len;
+ bpf_probe_read(&info.name, sizeof(info.name), d_name.name);
  if (S_ISREG(mode)) {
  info.type = 'R';
  } else if (S_ISSOCK(mode)) {

tools/mdflush.py

@@ -44,11 +44,11 @@
  * and maintenance burden.
  */
 #ifdef bio_dev
- bpf_probe_read(&data.disk, sizeof(data.disk), bio->bi_disk->disk_name);
+ struct gendisk *bi_disk = bio->bi_disk;
 #else
- bpf_probe_read(&data.disk, sizeof(data.disk),
- bio->bi_bdev->bd_disk->disk_name);
+ struct gendisk *bi_disk = bio->bi_bdev->bd_disk;
 #endif
+ bpf_probe_read(&data.disk, sizeof(data.disk), bi_disk->disk_name);
  events.perf_submit(ctx, &data, sizeof(data));
  return 0;
 }

tools/slabratetop.py

@@ -87,7 +87,8 @@ def signal_ignore(signal, frame):
 int kprobe__kmem_cache_alloc(struct pt_regs *ctx, struct kmem_cache *cachep)
 {
  struct info_t info = {};
- bpf_probe_read(&info.name, sizeof(info.name), (void *)cachep->name);
+ const char *name = cachep->name;
+ bpf_probe_read(&info.name, sizeof(info.name), name);
 
  struct val_t *valp, zero = {};
  valp = counts.lookup_or_init(&info, &zero);