Re: [Simulavr-devel] simple assembler program behaves incorrectly

[Petr Hluzín]

Hello

How did you build the ELF file?
What are the versions of gcc, binutils and gdb? WinAR?

I tried this:
avr-gcc -mmcu=atmega8 -Wa,--gdwarf2 experiment.S -o experiment.elf
avr-objdump --all-headers --disassemble --source --debugging --syms
experiment.elf > experiment.listing

$ avr-gcc --version
avr-gcc (WinAVR 20100110) 4.3.3

The compilation produced this:
00000000 <__vectors>:
   0:   12 c0           rjmp    .+36            ; 0x26 <__ctors_end>
   2:   19 c0           rjmp    .+50            ; 0x36 <__bad_interrupt>
   4:   18 c0           rjmp    .+48            ; 0x36 <__bad_interrupt>
....
00000026 <__ctors_end>:
  26:   11 24           eor     r1, r1
  28:   1f be           out     0x3f, r1        ; 63 SREG
  2a:   cf e5           ldi     r28, 0x5F       ; 95
  2c:   d4 e0           ldi     r29, 0x04       ; 4
  2e:   de bf           out     0x3e, r29       ; 62 SPH
  30:   cd bf           out     0x3d, r28       ; 61 SPL
  32:   05 d0           rcall   .+10            ; 0x3e <main>
  34:   08 c0           rjmp    .+16            ; 0x46 <_exit>

The string `output' is compiled and stored in flash segment. If there
are multiple initialized variables then they are grouped in a
continuous block in flash. When the AVR is powered up, C runtime is
expected to copy the block to RAM. The copying code should be in
__ctors_end, but it is missing (in my attempt to reproduce your
problem).

For some reason linker is not emitting code to do the copying. This is
not simulavr bug.

For illustration here is the initialization part of a C program which
is compiled with the proper code to copy .data section and zeroize
.bss section:
0000008c <__ctors_end>:
  8c:   11 24           eor     r1, r1
  8e:   1f be           out     0x3f, r1        ; 63 SREG
  90:   cf ef           ldi     r28, 0xFF       ; 255
  92:   d0 e1           ldi     r29, 0x10       ; 16
  94:   de bf           out     0x3e, r29       ; 62 SPH
  96:   cd bf           out     0x3d, r28       ; 61 SPL
00000098 <__do_copy_data>:
  98:   11 e0           ldi     r17, 0x01       ; 1
  9a:   a0 e0           ldi     r26, 0x00       ; 0
  9c:   b1 e0           ldi     r27, 0x01       ; 1
  9e:   e8 e1           ldi     r30, 0x18       ; 24
  a0:   f7 e0           ldi     r31, 0x07       ; 7
  a2:   00 e0           ldi     r16, 0x00       ; 0
  a4:   0b bf           out     0x3b, r16       ; 59
  a6:   02 c0           rjmp    .+4             ; 0xac <__do_copy_data+0x14>
  a8:   07 90           elpm    r0, Z+
  aa:   0d 92           st      X+, r0
  ac:   a0 30           cpi     r26, 0x00       ; 0
  ae:   b1 07           cpc     r27, r17
  b0:   d9 f7           brne    .-10            ; 0xa8 <__do_copy_data+0x10>
000000b2 <__do_clear_bss>:
  b2:   11 e0           ldi     r17, 0x01       ; 1
  b4:   a0 e0           ldi     r26, 0x00       ; 0
  b6:   b1 e0           ldi     r27, 0x01       ; 1
  b8:   01 c0           rjmp    .+2             ; 0xbc <.do_clear_bss_start>
000000ba <.do_clear_bss_loop>:
  ba:   1d 92           st      X+, r1
000000bc <.do_clear_bss_start>:
  bc:   ac 3f           cpi     r26, 0xFC       ; 252
  be:   b1 07           cpc     r27, r17
  c0:   e1 f7           brne    .-8             ; 0xba <.do_clear_bss_loop>
  c2:   0e 94 79 00     call    0xf2    ; 0xf2 <main>
  c6:   0c 94 8a 03     jmp     0x714   ; 0x714 <_exit>


-- 
Petr Hluzin