[wellylug]The top 10 dead (or dying) computer skills

Donald Gordon don at dis.org.nz
Thu Jul 12 21:01:54 NZST 2007


Richard Hector wrote:
> You have to write something that can create assembler (and/or machine
> code - if you're creating assembly language you'll need an assembler (or
> assemble by hand)), so you'll need to know _how_ to write it, but not
> necessarily write it directly.
>
> But you don't necessarily need to know that to create a boot loader or
> libc.
>   
Well, actually, at least on x86, there are some weird instructions you 
need to produce that it's probably fairly hard to make your compiler 
emit: the instructions to switch into protected mode (for the 
bootloader), and the instructions to make system calls (for libc).

In the bootloader case on x86 this is even worse, as the processor 
starts up in 16-bit mode, but generally you want to be running 32 bit 
code in protected mode.  So you'd have to compile the bits of the code 
that ran before and after the switch differently, too, and set up the 
stack for 32 bit mode, and all that sort of fun.

donald




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