[committed] libstdc++: Fix unspecified comparison to null pointer [PR 97415]

[Jonathan Wakely via Gcc-patches]

The standard doesn't guarantee that null pointers compare less than
non-null pointers. AddressSanitizer complains about the pptr()> egptr()
comparison in basic_stringbuf::str() when egptr() is null.

libstdc++-v3/ChangeLog:

        PR libstdc++/97415
        * include/std/sstream (basic_stringbuf::str()): Check for
        null egptr() before comparing to non-null pptr().

Tested powerpc64le-linux. Committed to trunk.



commit 78198b6021a9695054dab039340202170b88423c
Author: Jonathan Wakely <jwak...@redhat.com>
Date:   Wed Oct 14 18:55:14 2020

    libstdc++: Fix unspecified comparison to null pointer [PR 97415]
    
    The standard doesn't guarantee that null pointers compare less than
    non-null pointers. AddressSanitizer complains about the pptr()> egptr()
    comparison in basic_stringbuf::str() when egptr() is null.
    
    libstdc++-v3/ChangeLog:
    
            PR libstdc++/97415
            * include/std/sstream (basic_stringbuf::str()): Check for
            null egptr() before comparing to non-null pptr().

diff --git a/libstdc++-v3/include/std/sstream b/libstdc++-v3/include/std/sstream
index 9cca54d17d1..06960e30bf2 100644
--- a/libstdc++-v3/include/std/sstream
+++ b/libstdc++-v3/include/std/sstream
@@ -178,13 +178,14 @@ _GLIBCXX_BEGIN_NAMESPACE_CXX11
       str() const
       {
        __string_type __ret(_M_string.get_allocator());
-       if (this->pptr())
+       if (char_type* __pptr = this->pptr())
          {
+           char_type* __egptr = this->egptr();
            // The current egptr() may not be the actual string end.
-           if (this->pptr() > this->egptr())
-             __ret.assign(this->pbase(), this->pptr());
+           if (!__egptr || __pptr > __egptr)
+             __ret.assign(this->pbase(), __pptr);
            else
-             __ret.assign(this->pbase(), this->egptr());
+             __ret.assign(this->pbase(), __egptr);
          }
        else
          __ret = _M_string;