Re: bootsect.S changes

Alan Modra (alan@SPRI.Levels.UniSA.Edu.Au)
Sat, 16 Oct 1999 16:21:26 +0930 (CST)


On Fri, 15 Oct 1999, Richard B. Johnson wrote:

> [re: gas 16-bit mode]
> I think this is still a 'work in progress'. I hope that somebody adds

Please let me know of any problems in the latest 2.9.5 assembler. It's
fairly good now, I think.

> a directive to gas that tells it to assemble 16-bit code so the source
> code doesn't have to be wrong to get it to make 16-bit code. The

.code16 # 16-bit mode
.code16gcc # bastardised 16-bit mode that uses 32-bit call, ret so
# gcc gets the expected stack frame - also adds addr
# prefix automatically when presented with 32-bit
# base/index The idea is to use gcc to generate code that
# runs in 16-bit/real mode - *** on x86, x >= 3 ***
.code32 # 32-bit mode (default)

>[snip]
> word operations. Therefore, an assembler needs to 'know' when to
> not use 0x66. In other words it needs to know the current operation
> mode of the processor.

Yup. gas tracks .code16/32 and addr prefix given on same line as insn.

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