Re: [libbdf] Mach-O format support ?

[Emmanuel Fleury <fleury at labri dot fr>]

Tristan Gingold wrote:
> 
> it is difficult to answer to such a vague question.  The handling of Mach-O in bfd is good enough to
> have tools such as objdump working as well as gdb.
> 
> If you can describe precisely your issue (a reproducer would be welcome), then I could start to
> investigate.

Yes, you're definitely right, my description was extremely loose.
I first thought that the binutils dev team had a "position" on not
supporting part of the Mach-O. So, I did dig a bit and I think I might
have found what is going on.


More precisely, on my Debian-based computer when attempting to
disassemble one of those problematic Mach-O, I get the following:

[================================================================]
[fleury@aldebaran bfd-macho]$ file ls.macos
ls.macos: Mach-O fat file with 2 architectures
[fleury@aldebaran bfd-macho]$ objdump -d ls.macos
objdump: ls.macos: File format not recognized
[================================================================]


And, indeed, objdump is not responsible of this problem because I
experiment the exact same problem with my own program when using the
bfd_perror() function.

Concerning my version of binutils:

[================================================================]
ii  binutils                                                2.20.1-5
                        The GNU assembler, linker and binary utilities
ii  binutils-dev                                            2.20.1-5
                        The GNU binary utilities (BFD development files)
ii  binutils-doc                                            2.20.1-5
                        Documentation for the GNU assembler, linker and
binary utilities
ii  binutils-multiarch                                      2.20.1-5
                        Binary utilities that support multi-arch targets
ii  mingw32-binutils                                        2.20-0.1
                        Minimalist GNU win32 (cross) binutils
[================================================================]


On a Mac OS X computer, I have:

[================================================================]
punta:insight labri$ file /bin/ls
/bin/ls: Mach-O universal binary with 2 architectures
/bin/ls (for architecture i386): Mach-O executable i386
/bin/ls (for architecture ppc7400):     Mach-O executable ppc
[================================================================]

And for software coming from MacPorts:

[================================================================]
punta:insight labri$ file /opt/local/bin/svn
/opt/local/bin/svn: Mach-O executable i386
[================================================================]

The binary from MacPorts can be accessed with no problem, on the
contrary of the one from /bin.

So, what I suspect is just that libbfd does not handle this 'multi-arch'
packaging feature that seems to be supported in Mach-O.

Is it right ?

And, then, a natural question would be: Is there anyone working on
support for this ?

Regards
-- 
Emmanuel Fleury

When it comes to software security, the devil is in the details.
  -- Bruce Schneier