PR libstdc++/87787 avoid undefined null args to memcpy and memmove

The C++ char_traits and ctype APIs do not disallow null pointer
arguments, so we need explicit checks to ensure we don't forward null
pointers to memcpy or memmove.

	PR libstdc++/87787
	* include/bits/char_traits.h (char_traits::move): Do not pass null
	pointers to memmove.
	* include/bits/locale_facets.h
	(ctype<char>::widen(const char*, const char*, char*)): Do not
	pass null pointers to memcpy.
	(ctype<char>::narrow(const char*, const char*, char, char*)):
	Likewise.
	(ctype<char>::do_widen(const char*, const char*, char*)):
	Likewise.
	(ctype<char>::do_narrow(const char*, const char*, char, char*)):
	Likewise.

From-SVN: r267651

libstdc++-v3/ChangeLog

 2019-01-07  Jonathan Wakely  <jwakely@redhat.com>
 
+	PR libstdc++/87787
+	* include/bits/char_traits.h (char_traits::move): Do not pass null
+	pointers to memmove.
+	* include/bits/locale_facets.h
+	(ctype<char>::widen(const char*, const char*, char*)): Do not
+	pass null pointers to memcpy.
+	(ctype<char>::narrow(const char*, const char*, char, char*)):
+	Likewise.
+	(ctype<char>::do_widen(const char*, const char*, char*)):
+	Likewise.
+	(ctype<char>::do_narrow(const char*, const char*, char, char*)):
+	Likewise.
+
 	* doc/xml/manual/spine.xml: Update copyright years.
 	* doc/xml/manual/status_cxx2017.xml: Adjust note about -lstdc++fs.
 	* doc/xml/manual/using.xml: Remove requirement to link with -lstdc++fs

libstdc++-v3/include/bits/char_traits.h

@@ -183,6 +183,8 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
     char_traits<_CharT>::
     move(char_type* __s1, const char_type* __s2, std::size_t __n)
     {
+      if (__n == 0)
+	return __s1;
       return static_cast<_CharT*>(__builtin_memmove(__s1, __s2,
 						    __n * sizeof(char_type)));
     }

libstdc++-v3/include/bits/locale_facets.h

@@ -896,7 +896,8 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
       {
 	if (_M_widen_ok == 1)
 	  {
-	    __builtin_memcpy(__to, __lo, __hi - __lo);
+	    if (__builtin_expect(__hi != __lo, true))
+	      __builtin_memcpy(__to, __lo, __hi - __lo);
 	    return __hi;
 	  }
 	if (!_M_widen_ok)
@@ -961,7 +962,8 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
       {
 	if (__builtin_expect(_M_narrow_ok == 1, true))
 	  {
-	    __builtin_memcpy(__to, __lo, __hi - __lo);
+	    if (__builtin_expect(__hi != __lo, true))
+	      __builtin_memcpy(__to, __lo, __hi - __lo);
 	    return __hi;
 	  }
 	if (!_M_narrow_ok)
@@ -1100,7 +1102,8 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
       virtual const char*
       do_widen(const char* __lo, const char* __hi, char_type* __to) const
       {
-	__builtin_memcpy(__to, __lo, __hi - __lo);
+	if (__builtin_expect(__hi != __lo, true))
+	  __builtin_memcpy(__to, __lo, __hi - __lo);
 	return __hi;
       }
 
@@ -1153,7 +1156,8 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
       do_narrow(const char_type* __lo, const char_type* __hi,
 		char __dfault __attribute__((__unused__)), char* __to) const
       {
-	__builtin_memcpy(__to, __lo, __hi - __lo);
+	if (__builtin_expect(__hi != __lo, true))
+	  __builtin_memcpy(__to, __lo, __hi - __lo);
 	return __hi;
       }