[Bug c++/60387] New: The gcc compiler for the ppc architecture is not compatible with PPC ABI and DWARF standards.

[m_nistor at yahoo dot com]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=60387

            Bug ID: 60387
           Summary: The gcc compiler for the ppc architecture is not
                    compatible with PPC ABI and DWARF standards.
           Product: gcc
           Version: 4.8.1
            Status: UNCONFIRMED
          Severity: critical
          Priority: P3
         Component: c++
          Assignee: unassigned at gcc dot gnu.org
          Reporter: m_nistor at yahoo dot com

The gcc compiler for the ppc architecture doesn't use DWARF Register Number
Mapping that is defined in the PPC ABI standards. Just an example for the first
vector register (vr0): the ppc gcc generates 100 instead of 1124. 

The gcc compiler doesn't emit .debug_frame section and it prefers to emit only
the .eh_fram e section.
The .eh_frame section is used by application to handle the exception. This
section is part of the C++ ABI.
The .eh_frame section is not a debug section and this section should not be
used by debugger for unwinding stack frame, this statement was also done by
Michael Eager who is Chair of DWARF Standards Committee Members. You can see
below more information about this:
http://wiki.dwarfstd.org/index.php?title=Exception_Handling

Relationship with DWARF
Although the C++ ABI data in the .eh_frame section uses the data format
described by the DWARF Standard (with some extensions), this section (and other
sections used by exception handling, such as .eh_frame_hdr and
.gcc_except_table) are not defined by the DWARF Standard. The DWARF Standard
does not describe the extensions to support exception handling nor the routines
which must be called by a program to use this data. The DWARF Debugging Format
Committee does not specify the contents of these sections or the functionality
which must be provided by the language run time system to support exception
handling. 
The .eh_frame section is not used for debugging. Whether it is generated or not
is independent of whether DWARF debug data is generated. All DWARF data is
contained in sections with names starting with .debug, which may be removed
from a program without affecting the program's normal execution. It is common
practice to "strip" debugging sections from a program before putting it into
production, either to reduce the program size, make reverse engineering more
difficult, or both. 
Removing the .eh_frame section (whether the DWARF .debug sections are left in
place or not) has a high likelihood of adversely affecting a program's
behaviour, especially when it encounters an unexpected condition. 
Unfortunately, it has been a common shorthand to refer to the C++ ABI exception
handling methodology using .eh_frame with "DWARF exception handling," or
similar phrases. Perhaps this because it is easier to say this than the
unwieldy "C++ exception handling using the DWARF Call Frame Information format
with extensions", or the misleading "C++ ABI for IA-64" or "SVR4 ABI AMD64
Processor Supplement", especially when discussing a processor other than
Itanium or AMD-64. This leads to occasional confusion, where people may look at
the DWARF Specification for a description of the C++ ABI exception handling
method, or where vulnerabilities in the EH scheme are incorrectly characterized
as DWARF vulnerabilities, as in the otherwise excellent paper mentioned below.