Patchwork [7/8] infcall: handle pass-by-reference arguments appropriately

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Submitter Tankut Baris Aktemur
Date April 23, 2019, 2:31 p.m.
Message ID <1556029914-21250-8-git-send-email-tankut.baris.aktemur@intel.com>
Download mbox | patch
Permalink /patch/32386/
State New
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Comments

Tankut Baris Aktemur - April 23, 2019, 2:31 p.m.
If an aggregate argument is implicitly pass-by-reference, allocate
a temporary object on the stack, initialize it via the copy constructor
(if exists) or trivially by memcpy'ing.  Pass the reference of the
temporary to the callee function.  After the callee returns, invoke
the destructor of the temporary.

gdb/ChangeLog:

	* infcall.c (call_function_by_hand_dummy): Update.
	(struct destructor_info): New struct.
	(call_destructors): New auxiliary function.

---
 gdb/infcall.c | 103 ++++++++++++++++++++++++++++++++++++++++++++++++--
 1 file changed, 100 insertions(+), 3 deletions(-)

Patch

diff --git a/gdb/infcall.c b/gdb/infcall.c
index bd88076dc7f..fdbf09045ff 100644
--- a/gdb/infcall.c
+++ b/gdb/infcall.c
@@ -42,6 +42,7 @@ 
 #include "thread-fsm.h"
 #include <algorithm>
 #include "common/scope-exit.h"
+#include <list>
 
 /* If we can't find a function's name from its address,
    we print this instead.  */
@@ -693,6 +694,33 @@  reserve_stack_space (const type *values_type, CORE_ADDR &sp)
   return addr;
 }
 
+/* The data structure which keeps a destructor function and
+   its implicit 'this' parameter.  */
+
+struct destructor_info
+{
+  destructor_info (struct value *function, struct value *self)
+    : function (function), self (self) { }
+
+  struct value *function;
+  struct value *self;
+};
+
+
+/* Auxiliary function that takes a list of destructor functions
+   with their 'this' parameters, and invokes the functions.  */
+
+static void
+call_destructors (const std::list<destructor_info> &dtors_to_invoke,
+		  struct type *default_return_type)
+{
+  for (auto vals : dtors_to_invoke)
+    {
+      call_function_by_hand (vals.function, default_return_type,
+			     gdb::make_array_view (&(vals.self), 1));
+    }
+}
+
 /* See infcall.h.  */
 
 struct value *
@@ -968,6 +996,12 @@  call_function_by_hand_dummy (struct value *function,
       internal_error (__FILE__, __LINE__, _("bad switch"));
     }
 
+  /* Coerce the arguments and handle pass-by-reference.
+     We want to remember the destruction required for pass-by-ref values.
+     For these, store the dtor function and the 'this' argument
+     in DTORS_TO_INVOKE.  */
+  std::list<destructor_info> dtors_to_invoke;
+
   for (int i = args.size () - 1; i >= 0; i--)
     {
       int prototyped;
@@ -1005,9 +1039,68 @@  call_function_by_hand_dummy (struct value *function,
       args[i] = value_arg_coerce (gdbarch, args[i],
 				  param_type, prototyped);
 
-      if (param_type != NULL
-	  && !(language_pass_by_reference (param_type).trivially_copyable))
-	args[i] = value_addr (args[i]);
+      if (param_type == NULL)
+	continue;
+
+      auto info = language_pass_by_reference (param_type);
+      if (!info.copy_constructible)
+	error (_("expression cannot be evaluated because the type '%s' "
+		 "is not copy constructible"), TYPE_NAME (param_type));
+
+      if (!info.destructible)
+	error (_("expression cannot be evaluated because the type '%s' "
+		 "is not destructible"), TYPE_NAME (param_type));
+
+      if (info.trivially_copyable)
+	continue;
+
+      /* This is a pass-by-ref value.  Check for error cases before
+	 pushing the temporary to the stack.  */
+
+      if (!info.trivially_copy_constructible && info.cctor_name == NULL)
+	error (_("evaluation of this expression requires a copy constructor"
+		 " for the type '%s'."), TYPE_NAME (param_type));
+
+      if (!info.trivially_destructible && info.dtor_name == NULL)
+	error (_("evaluation of this expression requires a destructor"
+		 " for the type '%s'."), TYPE_NAME (param_type));
+
+      /* Make a copy of the argument on the stack.  If the argument is
+	 trivially copy ctor'able, copy bit by bit.  Otherwise, call
+	 the copy ctor to initialize the clone.  */
+      CORE_ADDR addr = reserve_stack_space (param_type, sp);
+      struct value *clone
+	= value_from_contents_and_address (param_type, NULL, addr);
+      push_thread_stack_temporary (call_thread.get (), clone);
+      struct value *clone_ptr
+	= value_from_pointer (lookup_pointer_type (param_type), addr);
+
+      if (info.trivially_copy_constructible)
+	{
+	  int length = TYPE_LENGTH (param_type);
+	  write_memory (addr, value_contents (args[i]), length);
+	}
+      else
+	{
+	  struct value *copy_ctor
+	    = find_function_in_inferior (info.cctor_name, 0);
+	  struct value *cctor_args[2] = { clone_ptr, args[i] };
+	  call_function_by_hand (copy_ctor, default_return_type,
+				 gdb::make_array_view (cctor_args, 2));
+	}
+
+      /* If the argument has a destructor, remember it so that we
+	 invoke it after the infcall is complete.  */
+      if (!info.trivially_destructible)
+	{
+	  struct value *dtor
+	    = find_function_in_inferior (info.dtor_name, 0);
+	  /* Insert the dtor to the front of the list to call them
+	     in reverse order later.  */
+	  dtors_to_invoke.emplace_front (dtor, clone_ptr);
+	}
+
+      args[i] = clone_ptr;
     }
 
   /* Reserve space for the return structure to be written on the
@@ -1174,6 +1267,10 @@  call_function_by_hand_dummy (struct value *function,
 	    maybe_remove_breakpoints ();
 
 	    gdb_assert (retval != NULL);
+
+	    /* Destruct the pass-by-ref argument clones.  */
+	    call_destructors (dtors_to_invoke, default_return_type);
+
 	    return retval;
 	  }