Re: [x86 setup 13/33] Header file to produce 16-bit code with gcc

Pawel Dziepak wrote:

On 7/10/07, Segher Boessenkool [off-list ref] wrote:

quoted

quoted

The alternative, of course, is to compile to an .s file and insert
.code16gcc into the .s file.  This makes the Makefile uglier, but
would
be more resilient against oddball gcc changes.

This would be even more fragile.  The exact format of GCC's
assembler code output isn't defined at all, so in principle
this is a hopeless task.  In practice just putting the
.code16gcc directive on the first line would likely work
though, GCC never generates a .code32 AFAIK, but it isn't
guaranteed that this will work (or will keep working).

Unfortunately, .code16gcc is still experimental (at least binutils'
website says that). What is worse, it says that it is possible that
16bit code produced on GCC won't work on pre-80386 processors (before
switching to protected mode you have to think about cpu as a
pre-80386).

What .code16gcc does is produce 32-bit instructions that are meant to be
run from a 16-bit code segment (real mode or 16-bit protected) by using
address and data size override prefixes.  This means that pre-386
processors cannot run the code because they cannot understand 32-bit
instructions.

--
				Brian Gerst