basic_string.h says:
/*
* [...]
* Where the _M_p points to the first character in the string, and
* you cast it to a pointer-to-_Rep and subtract 1 to get a
* pointer to the header.
* [...]
*/
The test case `testsuite/ext/array_allocator/2.cc' illustrates the bug. After
linking, the global variable `extern_array' is located at an odd-numbered
address (which is fine; it is a char array).
When _M_rep() is called by basic_string's destructor, a _Rep* is returned that
is unaligned for calling _Rep methods like dispose(), because an odd-numbered
address minus 1*sizeof (_Rep) is still odd-numbered:
_Rep*
_M_rep() const
{ return &((reinterpret_cast<_Rep*> (_M_data()))[-1]); }
This method call:
~basic_string()
{ _M_rep()->_M_dispose(this->get_allocator()); }
induces a bus error on architectures where misalignment triggers a bus error.
Is this a libstdc++ bug or a documentation omission?
--
Summary: basic_string::_M_rep() can produce an unnaturally
aligned pointer to _Rep
Product: gcc
Version: 4.0.0
Status: UNCONFIRMED
Severity: normal
Priority: P2
Component: libstdc++
AssignedTo: unassigned at gcc dot gnu dot org
ReportedBy: bje at gcc dot gnu dot org
CC: gcc-bugs at gcc dot gnu dot org
GCC host triplet: powerpc-linux
GCC target triplet: powerpc-linux
http://gcc.gnu.org/bugzilla/show_bug.cgi?id=19495
