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* [PATCH] teach compute_objsize about placement new (PR 100876)
@ 2021-06-02 21:40 Martin Sebor
  2021-06-02 21:46 ` Marek Polacek
                   ` (2 more replies)
  0 siblings, 3 replies; 10+ messages in thread
From: Martin Sebor @ 2021-06-02 21:40 UTC (permalink / raw)
  To: gcc-patches

[-- Attachment #1: Type: text/plain, Size: 1235 bytes --]

The two forms of placement operator new defined in <new> return their
pointer argument and may not be displaced by user-defined functions.
But because they are ordinary (not built-in) functions this property
isn't reflected in their declarations alone, and there's no user-
level attribute to annotate them with.  When they are inlined
the property is transparent in the IL but when they are not (without
inlining such as -O0), calls to the operators appear in the IL and
cause -Wmismatched-new-delete to try to match them with the functions
called to deallocate memory.  When the pointer to the memory was
obtained from a function that matches the deallocator but not
the placement new, the warning falsely triggers.

The attached patch solves this by detecting calls to placement new
and treating them the same as those to other pass-through calls (such
as memset).  In addition, it also teaches -Wfree-nonheap-object about
placement delete, for a similar reason as above.  Finally, it also
adds a test for attribute fn spec indicating a function returns its
argument.  It's not necessary for the fix (I had initially though
placement new might have the attribute) but it seems appropriate
to check.

Tested on x86_64-linux.

Martin

[-- Attachment #2: gcc-100876.diff --]
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PR c++/100876 - -Wmismatched-new-delete should understand placement new when it's not inlined

gcc/ChangeLog:

	PR c++/100876
	* builtins.c (gimple_call_return_array): Check for attribute fn spec.
	Handle calls to placement new.
	(ndecl_dealloc_argno): Avoid placement delete.

gcc/testsuite/ChangeLog:

	PR c++/100876
	* g++.dg/warn/Wmismatched-new-delete-4.C: New test.
	* g++.dg/warn/Wmismatched-new-delete-5.C: New test.
	* g++.dg/warn/Wstringop-overflow-7.C: New test.
	* g++.dg/warn/Wfree-nonheap-object-6.C: New test.
	* g++.dg/analyzer/placement-new.C: Prune out expected warning.

diff --git a/gcc/builtins.c b/gcc/builtins.c
index af1fe49bb48..fb0717a0248 100644
--- a/gcc/builtins.c
+++ b/gcc/builtins.c
@@ -5159,11 +5159,43 @@ static tree
 gimple_call_return_array (gimple *stmt, offset_int offrng[2],
 			  range_query *rvals)
 {
-  if (!gimple_call_builtin_p (stmt, BUILT_IN_NORMAL)
-      || gimple_call_num_args (stmt) < 1)
+  {
+    /* Check for attribute fn spec to see if the function returns one
+       of its arguments.  */
+    attr_fnspec fnspec = gimple_call_fnspec (as_a <gcall *>(stmt));
+    unsigned int argno;
+    if (fnspec.returns_arg (&argno))
+      {
+	offrng[0] = offrng[1] = 0;
+	return gimple_call_arg (stmt, argno);
+      }
+  }
+
+  if (gimple_call_num_args (stmt) < 1)
     return NULL_TREE;
 
   tree fn = gimple_call_fndecl (stmt);
+  if (!gimple_call_builtin_p (stmt, BUILT_IN_NORMAL))
+    {
+      /* See if this is a call to placement new.  */
+      if (!fn
+	  || !DECL_IS_OPERATOR_NEW_P (fn)
+	  || DECL_IS_REPLACEABLE_OPERATOR_NEW_P (fn))
+	return NULL_TREE;
+
+      tree fname = DECL_ASSEMBLER_NAME (fn);
+      const char *name = IDENTIFIER_POINTER (fname);
+      if (strcmp (name, "_ZnwmPv")       // ordinary form
+	  && strcmp (name, "_ZnamPv"))   // array form
+	return NULL_TREE;
+
+      if (gimple_call_num_args (stmt) != 2)
+	return NULL_TREE;
+
+      offrng[0] = offrng[1] = 0;
+      return gimple_call_arg (stmt, 1);
+    }
+
   switch (DECL_FUNCTION_CODE (fn))
     {
     case BUILT_IN_MEMCPY:
@@ -13285,7 +13317,18 @@ fndecl_dealloc_argno (tree fndecl)
 {
   /* A call to operator delete isn't recognized as one to a built-in.  */
   if (DECL_IS_OPERATOR_DELETE_P (fndecl))
-    return 0;
+    {
+      if (DECL_IS_REPLACEABLE_OPERATOR (fndecl))
+	return 0;
+
+      /* Avoid placement delete that's not been inlined.  */
+      tree fname = DECL_ASSEMBLER_NAME (fndecl);
+      const char *name = IDENTIFIER_POINTER (fname);
+      if (strcmp (name, "_ZdlPvS_") == 0       // ordinary form
+	  || strcmp (name, "_ZdaPvS_") == 0)   // array form
+	return UINT_MAX;
+      return 0;
+    }
 
   /* TODO: Handle user-defined functions with attribute malloc?  Handle
      known non-built-ins like fopen?  */
diff --git a/gcc/testsuite/g++.dg/analyzer/placement-new.C b/gcc/testsuite/g++.dg/analyzer/placement-new.C
index 8250f45b9d9..b648a428247 100644
--- a/gcc/testsuite/g++.dg/analyzer/placement-new.C
+++ b/gcc/testsuite/g++.dg/analyzer/placement-new.C
@@ -24,3 +24,5 @@ void test_3 (void)
   int *p = new(buf) int (42);
   delete p; // { dg-warning "memory not on the heap" }
 }
+
+// { dg-prune-output "-Wfree-nonheap-object" }
diff --git a/gcc/testsuite/g++.dg/warn/Wfree-nonheap-object-6.C b/gcc/testsuite/g++.dg/warn/Wfree-nonheap-object-6.C
new file mode 100644
index 00000000000..83b6ff9157c
--- /dev/null
+++ b/gcc/testsuite/g++.dg/warn/Wfree-nonheap-object-6.C
@@ -0,0 +1,45 @@
+/* { dg-do compile }
+   { dg-options "-O0 -Wall" } */
+
+#if __cplusplus < 201103L
+# define noexcept throw ()
+#endif
+
+void* operator new (__SIZE_TYPE__, void* __p) noexcept;
+void operator delete (void*, void*);
+
+void* operator new[] (__SIZE_TYPE__, void* __p) noexcept;
+void operator delete[] (void*, void*) noexcept;
+
+struct A { A (); ~A (); int i; };
+
+extern void *p;
+
+void nowarn_placement_new ()
+{
+  char a[sizeof (A)];
+  p = new (a) A ();           // { dg-bogus "-Wfree-nonheap-object" }
+}
+
+
+void warn_placement_new ()
+{
+  char a[sizeof (A)];
+  p = new (a + 1) A ();       // { dg-warning "\\\[-Wplacement-new" }
+                              // { dg-bogus "-Wfree-nonheap-object" "bogus" { target *-*-* } .-1 }
+}
+
+
+void nowarn_placement_new_array ()
+{
+  char a[sizeof (A)];
+  p = new (a) A[1];           // { dg-bogus "-Wfree-nonheap-object" }
+}
+
+
+void warn_placement_new_array ()
+{
+  char a[sizeof (A)];
+  p = new (a + 1) A[1];       // { dg-warning "\\\[-Wplacement-new" }
+                              // { dg-bogus "-Wfree-nonheap-object" "bogus" { target *-*-* } .-1 }
+}
diff --git a/gcc/testsuite/g++.dg/warn/Wmismatched-new-delete-4.C b/gcc/testsuite/g++.dg/warn/Wmismatched-new-delete-4.C
new file mode 100644
index 00000000000..4320181e4d7
--- /dev/null
+++ b/gcc/testsuite/g++.dg/warn/Wmismatched-new-delete-4.C
@@ -0,0 +1,37 @@
+/* PR c++/100876 - -Wmismatched-new-delete should either look through
+   or ignore placement new
+   { dg-do compile }
+   { dg-options "-O0 -Wall" } */
+
+extern "C" {
+  void* malloc (__SIZE_TYPE__);
+  void free (void*);
+}
+
+void* operator new (__SIZE_TYPE__, void*);
+void* operator new[] (__SIZE_TYPE__, void*);
+
+void nowarn_placement_new ()
+{
+  free (new (malloc (sizeof (int))) int ());      // { dg-bogus "-Wmismatched-new-delete" }
+}
+
+void nowarn_placement_array_new ()
+{
+  free (new (malloc (sizeof (int) * 2)) int[2]);  // { dg-bogus "-Wmismatched-new-delete" }
+}
+
+
+void warn_placement_new ()
+{
+  void *p = malloc (sizeof (int));
+  int *q = new (p) int ();
+  delete q;                   // { dg-warning "-Wmismatched-new-delete" }
+}
+
+void warn_placement_array_new ()
+{
+  void *p = malloc (sizeof (int));
+  int *q = new (p) int[2];
+  delete q;                   // { dg-warning "-Wmismatched-new-delete" }
+}
diff --git a/gcc/testsuite/g++.dg/warn/Wmismatched-new-delete-5.C b/gcc/testsuite/g++.dg/warn/Wmismatched-new-delete-5.C
new file mode 100644
index 00000000000..92c75df40d9
--- /dev/null
+++ b/gcc/testsuite/g++.dg/warn/Wmismatched-new-delete-5.C
@@ -0,0 +1,37 @@
+/* PR c++/100876 - -Wmismatched-new-delete should either look through
+   or ignore placement new
+   { dg-do compile }
+   { dg-options "-O2 -Wall" } */
+
+extern "C" {
+  void* malloc (__SIZE_TYPE__);
+  void free (void*);
+}
+
+inline void* operator new (__SIZE_TYPE__, void *p) { return p; }
+inline void* operator new[] (__SIZE_TYPE__, void *p) { return p; }
+
+void nowarn_placement_new ()
+{
+  free (new (malloc (sizeof (int))) int ());      // { dg-bogus "-Wmismatched-new-delete" }
+}
+
+void nowarn_placement_array_new ()
+{
+  free (new (malloc (sizeof (int) * 2)) int[2]);  // { dg-bogus "-Wmismatched-new-delete" }
+}
+
+
+void warn_placement_new ()
+{
+  void *p = malloc (sizeof (int));
+  int *q = new (p) int ();
+  delete q;                   // { dg-warning "-Wmismatched-new-delete" }
+}
+
+void warn_placement_array_new ()
+{
+  void *p = malloc (sizeof (int));
+  int *q = new (p) int[2];
+  delete q;                   // { dg-warning "-Wmismatched-new-delete" }
+}
diff --git a/gcc/testsuite/g++.dg/warn/Wstringop-overflow-7.C b/gcc/testsuite/g++.dg/warn/Wstringop-overflow-7.C
new file mode 100644
index 00000000000..d3d28f43d0a
--- /dev/null
+++ b/gcc/testsuite/g++.dg/warn/Wstringop-overflow-7.C
@@ -0,0 +1,42 @@
+/* PR c++/100876 - -Wmismatched-new-delete should either look through
+   or ignore placement new
+   { dg-do compile }
+   { dg-options "-O0 -Wall -Wno-array-bounds" } */
+
+inline void* operator new (__SIZE_TYPE__, void *p) { return p; }
+inline void* operator new[] (__SIZE_TYPE__, void *p) { return p; }
+
+void* nowarn_placement_new_memset ()
+{
+  struct S { int i; };
+  void *p = __builtin_malloc (sizeof (S));
+  S *q = new (p) S;
+  __builtin_memset (q, 0, sizeof (S));
+  return q;
+}
+
+void* warn_placement_new_memset ()
+{
+  struct S { int i; };
+  void *p = __builtin_malloc (sizeof (S));
+  S *q = new (p) S;
+  __builtin_memset (q, 0, sizeof (S) + 1);  // { dg-warning "\\\[-Wstringop-overflow" }
+  return q;
+}
+
+void* nowarn_placement_new_array_strncpy (const char *s)
+{
+  void *p = __builtin_malloc (5);
+  char *q = new (p) char[5];
+  __builtin_strncpy (q, s, 5);
+  return q;
+
+}
+
+void* warn_placement_new_array_strncpy (const char *s)
+{
+  void *p = __builtin_malloc (4);
+  char *q = new (p) char[5];
+  __builtin_strncpy (q, s, 5);  // { dg-warning "\\\[-Wstringop-overflow" }
+  return q;
+}

^ permalink raw reply	[flat|nested] 10+ messages in thread
end of thread, other threads:[~2021-06-15 18:48 UTC | newest]

Thread overview: 10+ messages (download: mbox.gz / follow: Atom feed)
-- links below jump to the message on this page --
2021-06-02 21:40 [PATCH] teach compute_objsize about placement new (PR 100876) Martin Sebor
2021-06-02 21:46 ` Marek Polacek
2021-06-14 22:56   ` Martin Sebor
2021-06-15 10:58     ` Christophe Lyon
2021-06-15 18:48       ` Martin Sebor
2021-06-09 15:47 ` PING " Martin Sebor
2021-06-13 23:45 ` Jeff Law
2021-06-14  5:56   ` Bernhard Reutner-Fischer
2021-06-14  6:04     ` Bernhard Reutner-Fischer
2021-06-14 22:56   ` Martin Sebor

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