[avr-gcc-list] How to convert Flash Strings from IAR to GCC?

[Bob Paddock]

I'm trying to convert some code from IAR 2.28 to GCC , but I can't get
the GCC version to read strings from flash, the way that IAR does.

I've read the FAQ on getting string in Flash, and the recent thread on
"Strings in Flash".

I know I could use pgm_read_byte_near() in the case I show here, but I 
need to stay backwards compatible with IAR, unfortunately, and it appears in 
several different places that one I show here.

How do I get GCC to generate functions that automatically uses LPM the way 
IAR does?


This is a snipped of IAR code, and it does the right thing (generates LPM 
instructions):
void flash_str_out( const char __flash *str )
{
     uint8_t chr_u8;
...
     chr_u8 = *str++;
...
}

This is what IAR generates:

    static char const __flash STRING[8] = "1234567";
    _nearfunc void flash_str_out(char const __flash *);
    ...
    \   00000010   01FC                       MOVW    R31 : R30,R25 : R24
    \   00000012   9104                       LPM     R16,Z
    ...


This is what GCC generates, which is wrong for reading from Flash (No LPM
instruction):

   25:strout.c      **** void flash_str_out( const prog_char * str )
   26:strout.c      **** {
  111                   .LM1:
  112                   /* prologue: frame size=0 */
  113 0000 CF93                 push r28
  114 0002 DF93                 push r29
  115                   /* prologue end (size=2) */
  116 0004 EC01                 movw r28,r24
   27:strout.c      ****     uint8_t chr_u8;
...
   32:strout.c      ****            chr_u8 = *str++;
  123                   .LM3:
  124 000a 8991                 ld r24,Y+


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