Re: [avr-gcc-list] Internal handling of interrupt vectors and jump table

[Georg-Johann Lay]

Am 08/11/2015 um 12:04 PM schrieb Klaus Rudolph:
> can someone explain how interrupt vectors are handled in gcc internally?

ISR functions are implemented as function attributes, i.e. there are 
avr-specific function attribute (__interrupt__, __signal__) which turn an 
ordinary function into an ISR.  Main outcome of these attributes is that 
./gcc/config/avr/avr.c::avr_expand_prologue() emits a different prologue for 
ISRs.  Similar for avr_expand_epilogue().

Attribute handling like special diagnostics for ISRs is performed by 
avr_set_current_function().


> OK, I saw that in  
> /opt/avr_5.2.0/lib/gcc/avr/5.2.0/../../../../avr/lib/avr5/crtatmega32.o
>
> the empty vector table is included, like:
>
> Disassembly of section .vectors:
> 00000000 <__vectors>:
> 0:   0c 94 00 00     jmp     0       ; 0x0 <__vectors>
> 4:   0c 94 00 00     jmp     0       ; 0x0 <__vectors>
> 8:   0c 94 00 00     jmp     0       ; 0x0 <__vectors>
>
> And I also can see, that my code results in:
>
> Disassembly of section .text:
> 00000000 <__vector_7>:

The .vectors section is implemented in AVR-LibC's gcrt1.S.
ISR and similar macros are provided by interrupt.h.


> but where can I see that __vector_7 goes to the correct place in the table?

To see the macros after expansion compile with -save-temps and read the 
respective .i file (C) or .ii file (C++).

Johann