Re: [avr-libc-dev] PSTR() in static initialisers

[Georg-Johann Lay]

On 31.01.2018 21:15, Paul "LeoNerd" Evans wrote:
> On Wed, 31 Jan 2018 21:04:55 +0100
> Joerg Wunsch <address@hidden> wrote:
>
> > As Paul "LeoNerd" Evans wrote:
> >
> > > Does anyone have a suggestion on how I can have a string pointer to
> > > a flash-stored string in a static initialiser?
> >
> > This only works by allocating each of the string into a variable
> > (well, constant actually) in flash by itself, and then mention their
> > names in the struct initializer.
>
> Hrm; that's upsettingly annoying. Is there perhaps a way this can be
> convinced into working? I generally dislike the untidiness of having to
> define lots of things above the main array definition, just so I can
> pull them in by name into it, and use that name nowhere else. Inline
> things would be nicer there.

If that static is not function-static, then __flash can be used:


#if !defined __FLASH || (defined __AVR_PM_BASE_ADDRESS__)
// For devices that see flash in RAM address space, resort to vanilla C.
#define __flash // empty
#endif // have __flash

#define FSTR(X) ((const __flash char[]) { X } )

const __flash char* const __flash animals[] =
{
  FSTR ("mite"), FSTR ("slug"), FSTR ("sloth")
};

const __flash char flash[] = "flash";
const __flash char *pram_to_flash = FSTR ("pet");
const __flash char * const __flash pflash_to_flash = FSTR ("cat");

const __flash char* ani (int i)
{
  return animals[i];
}

Notice that in contrast to progmem, __flash is a qualifier and *not* an 
attribute.  In particular, it matters where it occurs in a declaration, 
e.g. whether left or right of a "*".  gcc will generate accesses as 
desired, no need for pgm_read macros or inline asm.  However gcc rejects 
FSTR for function-static so that there is no one-fits-all solution:

const __flash char* get_pet (void)
{
  static const __flash char *pet = FSTR ("pet");
  return pet;
}

In function 'get_pet':
error: compound literal qualified by address-space qualifier
   return FSTR ("pet");
   ^~~~~~


Johann