Patchwork [review] infcall: handle pass-by-reference arguments appropriately

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Submitter Simon Marchi (Code Review)
Date Oct. 18, 2019, 1:53 p.m.
Message ID <gerrit.1571406803000.I18fa5d0df814dfa0defe9e862a88a6dbf1d99d01@gnutoolchain-gerrit.osci.io>
Download mbox | patch
Permalink /patch/35141/
State New
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Comments

Simon Marchi (Code Review) - Oct. 18, 2019, 1:53 p.m.
Tankut Baris Aktemur has uploaded a new change for review.

Change URL: https://gnutoolchain-gerrit.osci.io/r/c/binutils-gdb/+/141
......................................................................

infcall: handle pass-by-reference arguments appropriately

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:
2019-MM-DD  Tankut Baris Aktemur  <tankut.baris.aktemur@intel.com>

	* infcall.c (call_function_by_hand_dummy): Update the argument-
	passing section for call-by-value parameters.
	(struct destructor_info): New struct.
	(call_destructors): New auxiliary function.

Change-Id: I18fa5d0df814dfa0defe9e862a88a6dbf1d99d01
---
M gdb/infcall.c
1 file changed, 100 insertions(+), 3 deletions(-)
Simon Marchi (Code Review) - Oct. 29, 2019, 7:54 p.m.
Tom Tromey has posted comments on this change.

Change URL: https://gnutoolchain-gerrit.osci.io/r/c/binutils-gdb/+/141
......................................................................


Patch Set 1: Code-Review+2

Thank you.  This looks reasonable to me.

Patch

diff --git a/gdb/infcall.c b/gdb/infcall.c
index 288b9e0..701df4d 100644
--- a/gdb/infcall.c
+++ b/gdb/infcall.c
@@ -42,6 +42,7 @@ 
 #include "thread-fsm.h"
 #include <algorithm>
 #include "gdbsupport/scope-exit.h"
+#include <list>
 
 /* If we can't find a function's name from its address,
    we print this instead.  */
@@ -704,6 +705,33 @@ 
   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 *
@@ -983,6 +1011,12 @@ 
       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;
@@ -1020,9 +1054,68 @@ 
       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
@@ -1189,6 +1282,10 @@ 
 	    maybe_remove_breakpoints ();
 
 	    gdb_assert (retval != NULL);
+
+	    /* Destruct the pass-by-ref argument clones.  */
+	    call_destructors (dtors_to_invoke, default_return_type);
+
 	    return retval;
 	  }