typedef struct our
{
    unsigned char c;
    struct our *s_our;
} our_struct;

extern our_struct s1;
const our_struct s2 = {'A', &s1};

extern our_struct s2;
const our_struct s1 = {'A', &s2};

typedef struct our
{
    unsigned char c;
    struct our const *s_our;
} our_struct;

extern our_struct const s1;
const our_struct s2 = {'A', &s1};
const our_struct s1 = {'A', &s2};

D:\Projects\test\uuu>make
avr-gcc --version
avr-gcc.exe (WinAVR 20100110) 4.3.3
Copyright (C) 2008 Free Software Foundation, Inc.
This is free software; see the source for copying conditions.  There is NO
warranty; not even for MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.

cat test.c
typedef struct our
{
    unsigned char c;
    struct our const *s_our;
} our_struct;

extern our_struct const s1;
const our_struct s2 = {'A', &s1};
const our_struct s1 = {'A', &s2};

int main()
{
    for(;;)
       ;
}
Compiling: test.c
avr-gcc  -mmcu=atmega8 -Wall -gdwarf-2  -DF_CPU=14745000UL  -Os  -fsigned-char -funsigned-bitfields -fshort-enums -MD -MP -MT ./release/obj/test.o -MF ./release/dep/test.o.d  -ffunction-sections  -fdata-sections -fno-ivopts --param inline-call-cost=0 -fno-move-loop-invariants -Wa,-ahlmsd=./release/lst/test.lst -c  test.c -o release/obj/test.o
Linking: release/struct_test.elf
avr-gcc -mmcu=atmega8 -Wl,-Map=./release/lst/struct_test.map -Wl,--gc-sections -Wl,--relax  ./release/obj/test.o    -o release/struct_test.elf
Generating hex: release/struct_test.hex
avr-objcopy -O ihex -R .eeprom  release/struct_test.elf release/struct_test.hex
Generating eep: release/struct_test.ee.hex
avr-objcopy -O ihex -j .eeprom --set-section-flags=.eeprom="alloc,load" --change-section-lma .eeprom=0 --no-change-warnings release/struct_test.elf release/struct_test.ee.hex || exit 0
Generating disassembly: release/lst/struct_test.lss
avr-objdump -h -S release/struct_test.elf > release/lst/struct_test.lss
AVR Memory Usage
----------------
Device: atmega8

Program:      84 bytes (1.0% Full)
(.text + .data + .bootloader)

Data:          0 bytes (0.0% Full)
(.data + .bss + .noinit)

extern our_struct const s1;