Re: [avr-libc-dev] Re: [bug #19050] gcrt1.S should call main ratherthan jumping to it

[Anatoly Sokolov]

----- Original Message ----- 
From: "Joerg Wunsch" <address@hidden>


> As Anatoly Sokolov wrote:
>
>> These changes should be reverted:
>>
>> -  if (main_p)
>> -    {
>> -      fprintf (file, ("\t"
>> -       AS1 (ldi,r28) ",lo8(%s - " HOST_WIDE_INT_PRINT_DEC ")" CR_TAB
>> -       AS1 (ldi,r29) ",hi8(%s - " HOST_WIDE_INT_PRINT_DEC ")" CR_TAB
>> -       AS2 (out,__SP_H__,r29)     CR_TAB
>> -       AS2 (out,__SP_L__,r28) "\n"),
>> -        avr_init_stack, size, avr_init_stack, size);
>> -
>> -      prologue_size += 4;
>> -    }
>> -  else if (minimize && (frame_pointer_needed || live_seq > 6))
>> +  if (minimize && (frame_pointer_needed || live_seq > 6))
>
> That would restore the old (buggy) stack pointer initialization.
>


NO! NO! NO! Code which you see in the beginning of main() function:
 ldi r28, 0x5D ; 93
 ldi r29, 0x08 ; 8
 out 0x3e, r29 ; 62
 out 0x3d, r28 ; 61

no stack pointer initialization!!!! It is function frames initialization!!!

It is no SP = RAMEND.... It is SP = FP= (RAMEND - size);

Where 'size' is size all local (unoptimized) variables.

This code compiled for ATmega32 device.
int main()
{
  int i;
}

RAMEND for ATmega32 is defined as 0x85F. And SP != 0x085F, but
SP = RAMEND - sizeof(int) = 0x085F - 2 = 0x85D!!!

But,  if the frame size is null it is possible to not initialize function 
frames:
- if (main_p)
+ if (main_p && size != 0)
    {
      fprintf (file, ("\t"
       AS1 (ldi,r28) ",lo8(%s - " HOST_WIDE_INT_PRINT_DEC ")" CR_TAB
       AS1 (ldi,r29) ",hi8(%s - " HOST_WIDE_INT_PRINT_DEC ")" CR_TAB
       AS2 (out,__SP_H__,r29)     CR_TAB
       AS2 (out,__SP_L__,r28) "\n"),
        avr_init_stack, size, avr_init_stack, size);

      prologue_size += 4;
    }

It needs to be tested, probably the fream pointer (r28:r29) is required to 
the compiler.

Anatoly.