AVR: gas: unusable assembler output and complicated ISR problem...

[Nick Clifton]

Hi Ian,

> I wish to compile C sources to assembler, modify the assembler, and then
> assemble and link object produced.

I am sure that you are aware of this, but just for the sake of other readers
I will say that mucking about with compiler produced assembler is a good way
to shoot yourself in the foot if you do not know what you are doing...


> __vector_36:
>          __gcc_isr 1      ;  // note b


> Is there some way to get gas to "preprocess" the file to expand the
> pseudo operations __gcci_isr*  ?

No.  Well yes, but I do not think that you are going to like it.
There is no way to get the preprocessed sources that you are talking
about.  But there is a way to get the post-processed sources instead.
The trick is to disassemble the assembled output and use this as the
template for your editing...

   % as irq.s -o irq.o -mgcc-isr
   % objdump -d irq.o --no-addresses --no-show-raw-insn > irq.preprocessed.s
   % cat irq.preprocessed.s
   irq.o:     file format elf32-avr

   Disassembly of section .text:

   <__vector_36>:
	push	r24
	ldi	r24, 0x05	; 5
	sts	0x0085, r24	; 0x<__gcc_isr.n_pushed.001+0x800084>
	pop	r24
	reti

(I have used a truncated version of irq.s for this demonstration...)

Cheers
   Nick

PS.  If you really want to modify the assembler so that it can generate
a pre-processed output, then your best bet is to look at the assembler
listing option (-a).  But you will need to find some way to hook in back
end generated text, which I do not think has been implemented yet...