Re: Universal Binary static data
Re: Universal Binary static data
- Subject: Re: Universal Binary static data
- From: Henri Asseily <email@hidden>
- Date: Fri, 15 Sep 2006 16:28:17 +0200
On Sep 15, 2006, at 2:50 PM, Matt Mashyna wrote:
I have an application that uses a universal, dynamic library. There
is some static data that gets modified as a security check. I know
this is a bad practice but that's how it works on my client's
windows scheme so...
I can locate this static data in the dylib. The linker makes two
sets of static data; PPC and Intel. The problem is that when it's
built on a PPC machine the PPC part is first followed by the Intel
part. When it's built on Intel the opposite is true.
I think it must be a linker issue. Is there a way to force Xcode to
always put them in a specific order no matter what platform it's
built on ? Or is there a way to tell what order they are in by
examining a header ?
From the Mac OS X ABI Mach-O File Format Reference:
--
A binary that contains code for more than one architecture always
begins with a fat_header data structure, followed by two fat_arch
data structures and the actual data for the architectures contained
in the file. All data in these data structures is stored in big-
endian byte order.
--
What you need to do is read the fat_header data structure, that will
specify how many fat_arch data structures exist (fat_header-
>nfat_arch). You then iterate through those and grab the
architecture type in each (fat_archs[i]->cpu_type). You can also get
the offset and size of each data structure to go straight into what
you want to change.
Look at /usr/include/mach-o/fat.h, and the otool command line source
code (in the cctools darwin package).
Better yet:
http://developer.apple.com/samplecode/CheckExecutableArchitecture/
listing1.html
HTH,
H
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