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* [gcc r11-7350] PR c++/99074 - crash in dynamic_cast<>() on null pointer
@ 2021-02-23 21:14 Martin Sebor
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From: Martin Sebor @ 2021-02-23 21:14 UTC (permalink / raw)
To: gcc-cvs, libstdc++-cvs
https://gcc.gnu.org/g:6d134ca4b963706f31251f061fc180e517b32546
commit r11-7350-g6d134ca4b963706f31251f061fc180e517b32546
Author: Martin Sebor <msebor@redhat.com>
Date: Tue Feb 23 14:09:00 2021 -0700
PR c++/99074 - crash in dynamic_cast<>() on null pointer
libstdc++-v3/ChangeLog:
PR c++/99074
* libsupc++/dyncast.cc (__dynamic_cast): Return null when
first argument is null.
gcc/testsuite/ChangeLog:
PR c++/99074
* g++.dg/warn/Wnonnull11.C: New test.
Diff:
---
gcc/testsuite/g++.dg/warn/Wnonnull11.C | 40 ++++++++++++++++++++++++++++++++++
libstdc++-v3/libsupc++/dyncast.cc | 3 +++
2 files changed, 43 insertions(+)
diff --git a/gcc/testsuite/g++.dg/warn/Wnonnull11.C b/gcc/testsuite/g++.dg/warn/Wnonnull11.C
new file mode 100644
index 00000000000..5f1b69d9a41
--- /dev/null
+++ b/gcc/testsuite/g++.dg/warn/Wnonnull11.C
@@ -0,0 +1,40 @@
+/* PR c++/99074 - gcc 8 and above is crashing with dynamic_cast<>() on null
+ pointer with optimization level -O1 and above
+ { dg-do run }
+ { dg-options "-O1 -Wall" } */
+
+class Base
+{
+public:
+ virtual ~Base() {}
+ virtual void op() = 0;
+};
+
+class Object: public virtual Base { };
+
+class AbstractBase: public virtual Base
+{
+public:
+ Object* _to_object ()
+ {
+ return dynamic_cast<Object*>(this); // { dg-warning "\\\[-Wnonnull" "" { xfail *-*-* } }
+ }
+};
+
+class MyAbstractClass: public virtual AbstractBase
+{
+public:
+ static MyAbstractClass* _nil () { return 0; }
+};
+
+
+int main ()
+{
+ MyAbstractClass *my_abs_type = MyAbstractClass::_nil ();
+ AbstractBase *abs_base = my_abs_type;
+ Object *obj = abs_base->_to_object ();
+
+ __builtin_printf ("object is: %p\n", obj);
+
+ return 0;
+}
diff --git a/libstdc++-v3/libsupc++/dyncast.cc b/libstdc++-v3/libsupc++/dyncast.cc
index b7d98495ad3..f8f707ee4d4 100644
--- a/libstdc++-v3/libsupc++/dyncast.cc
+++ b/libstdc++-v3/libsupc++/dyncast.cc
@@ -47,6 +47,9 @@ __dynamic_cast (const void *src_ptr, // object started from
const __class_type_info *dst_type, // desired target type
ptrdiff_t src2dst) // how src and dst are related
{
+ if (!src_ptr)
+ /* Handle precondition violations gracefully. */
+ return NULL;
const void *vtable = *static_cast <const void *const *> (src_ptr);
const vtable_prefix *prefix =
(adjust_pointer <vtable_prefix>
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