Merge pull request #1212 from iovisor/yhs_dev

Force udst ctx->#reg load to be volatile

src/cc/usdt.cc

@@ -152,7 +152,7 @@ bool Probe::usdt_getarg(std::ostream &stream) {
 
   for (size_t arg_n = 0; arg_n < arg_count; ++arg_n) {
     std::string ctype = largest_arg_type(arg_n);
-    std::string cptr = tfm::format("*((volatile %s *)dest)", ctype);
+    std::string cptr("dest");
 
     tfm::format(stream,
                 "static __always_inline int _bpf_readarg_%s_%d("

src/cc/usdt_args.cc

@@ -67,17 +67,17 @@ bool Argument::assign_to_local(std::ostream &stream,
   }
 
   if (!deref_offset_) {
-    tfm::format(stream, "%s = (%s)ctx->%s;", local_name, ctype(),
+    tfm::format(stream, "%s = *(volatile %s *)&ctx->%s;", local_name, ctype(),
                 *base_register_name_);
     return true;
   }
 
   if (deref_offset_ && !deref_ident_) {
-    tfm::format(stream, "{ u64 __addr = ctx->%s + (%d)",
+    tfm::format(stream, "{ u64 __addr = (*(volatile u64 *)&ctx->%s) + (%d)",
                 *base_register_name_, *deref_offset_);
     if (index_register_name_) {
       int scale = scale_.value_or(1);
-      tfm::format(stream, " + (ctx->%s * %d);", *index_register_name_, scale);
+      tfm::format(stream, " + ((*(volatile u64 *)&ctx->%s) * %d);", *index_register_name_, scale);
     } else {
       tfm::format(stream, ";");
     }