Re: How the DragonflyBSD developers solve problems that are not resolved by Assembly?

Both FreeBSD and DragonFly developers in the past have simply use .byte
assembly directives to lay down opcodes with no assembly equivalents.  For
example, in asmacros.h there is:

#define NON_GPROF_RET               .byte 0xc3

Which is used in assembly files for situations where the various RETs have
been #defined to be other things for profiling.

This is a last resort usually.  It has been used for a few floating point
ops here and there in the past, and ultimately the assembly gains the
needed opcodes and they can be replaced with the proper name.  I don't
think there is a whole lot of it in the current code bases.

-Matt

On Mon, Oct 20, 2014 at 4:10 PM, françai s <[email protected]> wrote:

> I think that the only case where you have to resort to writing binary
> code manually
> is when the assembler cannot output the desired code for some reason.
> If I recall correctly, there is only one such case in the HelenOS
> sources:
>
>
> http://trac.helenos.org/browser/mainline/kernel/arch/mips32/include/debug.h?rev=mainline%2C1446.3.1
>
> Here they manually encode the opcodes of five special debugging
> instructions for the MSIM MIPS simulator (these instructions are not
> part of the standard MIPS ISA, thus the assembler does not know them).
>
> But the developers of FreeBSD not write binary code manually.
>
> How the DragonflyBSD developers solve problems that are not resolved
> by Assembly?
>