How OS X Executes Applications

MacHore writes "0xFE has an excellent tutorial on Mach-O, which is the file format used by OS X executable files and libraries. It goes into great detail about how Mach-O works, and explains what OS X actually does when it loads and runs an application. Subtopics include Universal Binaries, The Dynamic Linker, Using otool, and other goodies."

Comments

Re:Interesting, but why?

[Fahrvergnuugen]

I didn't know it was a big secret.

Re:Kinda OT.. yet relevant to this thread

[GlassHeart]

So - you install a version of the gimp - you get a copy of gtk, install eog - you get a copy of gtk, install.... well I think you get my point.

No, the post you were responding to phrased it poorly.

What is inherent in a MacOS X version (say, 10.4.5) already covers most of what an application might need, including Apple's "equivalent" of gtk. Go browse the Apple Developer docs sometime, and you'll see a much richer set of libraries that come with the OS by default. Thus, if an application wants an "obscure" library and decides to bundle it, the cost to the system is minimal even if another app has the same one. The MacOS bundle is not at all the equivalent of statically linking against gtk and other "fundamental" libraries in Linux.

On the Mac you have scour the web deciding Free or Paid, [...] Once you've downloaded it, things are pretty sweet, but finding the download can be a PITA.

Have you ever heard of versiontracker?

On the linux box (I am going to choose Debian as I'm familiar with it). Fire up synaptic from the gnome menu. Search for barcode. Two results returned. Both of these programs I know to be free of trojans, compatable with my system & configured for it. To install, I double click.

Which can bring in new versions of a library, which in turn brings in new versions of another application, which may be broken in some way (like any app can be). In other words, installing one app in Linux can effectively break another one. You pay for the isolation available to MacOS X apps in the form of disk space and RAM, both of which can be relatively cheap depending on what you're doing with your computer.

Re:are osx binaries cross-architecture?

[geoffspear]

The answer is "sort of".

The architecture does support Universal Binaries, which have code for both PPC and intel processors. This isn't really anything new or magical, the OS is just smart enough to know which code to execute. The same thing existed in the classic MacOS to support both PPC and 680x0 systems with FAT binaries.

As with the classic MacOS, there's also an emulator involved, so the newer architecture can run (most) binaries compiled on the older architecture.

However, compile something just for the Intel processors, and it won't run on your PPC hardware. If I understand your question correctly, if things worked the way you were assuming, Mach-O itself would guarantee any Mach-O binary would run on either system.