Re: avr-gcc-12.1.0-x64-windows new warnings ?

[Thilo Schulz]

Hi,

Am Monday, 24 April 2023, 07:46:23 CEST schrieb Senthil Kumar:
> > warning: array subscript 0 is outside array bounds of 'volatile
> > uint8_t[0]' {aka 'volatile unsigned char[]'} [-Warray-bounds]
> 
> Presumably from the macro expansion of PORTC?
> Can you paste the full command line? Also, can you add -E to the command
> line and share the output?

I've frequently seen this type of error on other platforms, as well.
The warning is only generated on one of the higher optimisation levels (-O2), 
and is a result of the compiler thinking it caught an error, where there is 
none (at least for this particular use case).

The error occurs when the linker is used to define base addresses for 
peripherals, but system headers provide macros for access to registers with an 
offset via array subscription, such as:

>From system headers:
extern volatile uint8_t PERIPHERALA;
#define PERIPHERALA_SOMEREG ((&PERIPHERALA)[1])

<linker script:>
PERIPHERALA = 0x0080U   (set symbol PERIPHERALA to the base address)

I haven't found a good way yet to fix this warning, except for disabling the
-Warray-bounds warning for the .c file, or for the section of code where those 
macros are invoked (#pragma). I'd be interested in a better solution.
If this error happens right on invocation of the PORTC macro, I guess, this 
warning needs to be addressed in the avr-gcc system header themselves:

extern volatile uint8_t PERIPHERALA[10];   /* size of peripheral addr space */
#define PERIPHERALA_SOMEREG (PERIPHERALA[1])

--
Best regards,
Thilo Schulz