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

Kinda OT.. yet relevant to this thread

[OlivierB]

Great strides are made weekly on the usability of linux, package management, dependencies, New File Systems, More apps, Wine etc.. and there is no doubt in my mind that they all work towards making Linux easier to use and more accessible to Lambda Joe's.

There is one thing without which no Joe User will go, no matter how pretty or compatible linux becomes: installing Apps.

No matter if you are a Windws, Linux or other die-hard you have to admit Mac OS X Make's it damn easy to instll 99% of the apps. Drag and drop what looks like a single file (in reality a *.app folder) and clik to run.

I immediately knew this was huge when OS X came out and made this possible on *NIX machines, and was secretly hoping that Linux wold catch up with it's own version and take-off.

Unfortunately, we are still relying on the age-old install with dependencies, of-course Synaptic, apt and Yum all make that easier but still too complex for 80% of the people.

When will we get drag and drop app install for Linux?

0xFE

[MagicM]

Offtopic, but can someone tell me how "0xfe.blogspot.com" is a valid domain?

According to RFC 1034:
<label> ::= <letter> [ [ <ldh-str> ] <let-dig> ]

I have some code to fix if "someone@0xfe.blogspot.com" could be a valid address...

Re:I don't have a Mac

[Homology]

What is this RTFM you are talking about?

Turn off swapping! (OT)

[x2A]

Yes I know this goes somewhat against the grain, but try shrinking your swap right down (max 128meg or something)... then, you get OOM messages, at which point you can close/reopen apps, rather than losing control of the system as it grinds to a halt trying to swap constantly.

This might not be so important in your (and possible, in most) case[s]. The server's I run I admin remotely. A runaway script can eat through the swap, slowing things to such a halt that logging in, finding the process, and killing it, can become next to impossible.

The smaller the swap, the less time there is before a runaway script (or memory leaking app) will run before the OOM killer gets it.

(I know this isn't really relevant stuff... I'm avoiding doing work :-/)

Re:How I execute applications :)

[Medievalist]

A 12V battery made from 8 1.5V AA dry cells is unlikely to do me any harm, even if it takes a fairly low resistance path through my body. The 12V lead acid battery in my car will give me a fairly hefty kick through the same path even though the resistance of my body hasn't changed.

Humans feel no noticeable shock from a 12VDC lead acid car battery. I handle fully charged ones reasonably frequently, occasionally with my hands wet or bleeding. If you dead short the terminals you make lots of hydrogen very fast, and under most circumstances you also create a welding arc, which are two things that do not co-exist well. But you can lay on the terminals with your naked body and nothing will happen.

This is the reason why it's a good idea to use a 1:1 isolating transformer when working on mains equipment - you can get seriously injured in the time it takes a fuse to blow, whereas the transformer will saturate and provides an absolute (and hopefully safe) limit to current flow.

120 VAC at 60 Hz will not injure a normal healthy human adult. Speaking from extensive experience and observation. But from the word mains I am suspecting you are a Briton, and while I don't think 240 VAC will seriously injure anyone from electric shock, it certainly hurts like the very dickens!

My own observation, based on subjective amounts of pain experienced through various kinds of inadvertently administered eletric shock, is that frequency matters. That 12VDC from your car battery becomes a whole different animal once it's been through an ignition coil, and the anode of a CRT will make you feel like your eyeballs are smoking. Perhaps 50Hz 240VAC is more injurious than 60Hz 240VAC... I hope not to find out.