[avr-libc-dev] [bug #34680] PSTR() should declare a const variable

[Volker Kuhlmann]

URL:
  <http://savannah.nongnu.org/bugs/?34680>

                 Summary: PSTR() should declare a const variable
                 Project: AVR C Runtime Library
            Submitted by: vok
            Submitted on: Sat 29 Oct 2011 17:20:03 NZDT
                Category: Header
                Severity: 3 - Normal
                Priority: 5 - Normal
              Item Group: Header files
                  Status: None
        Percent Complete: 0%
             Assigned to: None
             Open/Closed: Open
         Discussion Lock: Any
                 Release: 1.7.1
           Fixed Release: None

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Details:

avr/pgmspace.h defines

# define PSTR(s) (__extension__({static char __c[] PROGMEM = (s); &__c[0];}))

which places the variable into read-only (program flash) memory. This should
be marked as const to indicate that the variable will not change.

Because of a gcc bug (4.2? - 4.5) it's necessary to redefine PROGMEM to
#define PROGMEM __attribute__(( section(".progmem.data") ))
to achieve the same effect but without the bogus warning from gcc.
This definition gives a linker error when mixing const and non-const variables
in the same section. Placing the const variables into ".progmem.data" and the
non-const into ".progmem.datanotreadwriteafterall" works with the same effect,
but I don't see how to do that automatically.

See bug #28837, and http://gcc.gnu.org/bugzilla/show_bug.cgi?id=34734
So to make this all work with correctly programmed source that uses const,
make PSTR const as well, which it should have been in tne first place.




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