[avr-gcc-list] When does the Stack Frame Pointer (Y) get setup?

[Bob Paddock]

When does the Stack Frame Pointer (Y) get setup?

Should the following code work?  I find it trashing memory in bss:

void id_filter_init8( void ) __attribute__ ((naked)) __attribute__
((section(".init8")));
void id_filter_init8( void )
{
  uint8_t ff_u8[128U];

  /* memset() should really be used here */
  for( uint16_t idx_u16 = 0U; idx_u16 < (uint16_t) sizeof( ff_u8 ); idx_u16++ )
    {
      ff_u8[ idx_u16 ] = 0U;
    }

  /* Anything that makes ff_u8 be used, so it is not optimized away in
this example: */
  eeprom_update_block ( ff_u8, sysgrp_mask_eeprom_u8, sizeof(
sysgrp_mask_eeprom_u8 ) );
}

.lss:

00008cc4 <__ctors_end>:
    8cc4:       11 24           eor     r1, r1
    8cc6:       1f be           out     0x3f, r1        ; 63
    8cc8:       cf ef           ldi     r28, 0xFF       ; 255 Set Y and stack
    8cca:       df e3           ldi     r29, 0x3F       ; 63
    8ccc:       de bf           out     0x3e, r29       ; 62
    8cce:       cd bf           out     0x3d, r28       ; 61
    8cd0:       00 e0           ldi     r16, 0x00       ; 0
    8cd2:       0c bf           out     0x3c, r16       ; 60
    8cd4:       18 be           out     0x38, r1        ; 56
    8cd6:       19 be           out     0x39, r1        ; 57
    8cd8:       1a be           out     0x3a, r1        ; 58
    8cda:       1b be           out     0x3b, r1        ; 59

[snip lots of stuff that changes r28/r29, doesn't save them]

[Is Y really a frame pointer value at this point?:]

void id_filter_init8( void ) __attribute__ ((naked)) __attribute__
((section(".init8")));
void id_filter_init8( void )
{
    93b4:       fe 01           movw    r30, r28
    93b6:       31 96           adiw    r30, 0x01       ; 1
#include "event.h"
extern void event_bug( void );
#endif

void id_filter_init8( void ) __attribute__ ((naked)) __attribute__
((section(".init8")));
void id_filter_init8( void )
    93b8:       ce 01           movw    r24, r28
    93ba:       8f 57           subi    r24, 0x7F       ; 127
    93bc:       9f 4f           sbci    r25, 0xFF       ; 255
{
  uint8_t ff_u8[128U];

  for( uint16_t idx_u16 = 0U; idx_u16 < (uint16_t) sizeof( ff_u8 ); idx_u16++ )
    {
      ff_u8[ idx_u16 ] = 0U;
    93be:       11 92           st      Z+, r1
void id_filter_init8( void ) __attribute__ ((naked)) __attribute__
((section(".init8")));
void id_filter_init8( void )
{
  uint8_t ff_u8[128U];

  for( uint16_t idx_u16 = 0U; idx_u16 < (uint16_t) sizeof( ff_u8 ); idx_u16++ )
    93c0:       e8 17           cp      r30, r24
    93c2:       f9 07           cpc     r31, r25
    93c4:       e1 f7           brne    .-8             ; 0x93be 
<id_filter_init8+0xa>
    {
      ff_u8[ idx_u16 ] = 0U;
    }

[Looks like Y Frame Pointer is set and used as such from here on, and
gets saved in function calls:]

MAIN_OS int main( void )
{
    95d2:       cd b7           in      r28, 0x3d       ; 61
    95d4:       de b7           in      r29, 0x3e       ; 62
    95d6:       cb 54           subi    r28, 0x4B       ; 75
    95d8:       d0 40           sbci    r29, 0x00       ; 0
    95da:       cd bf           out     0x3d, r28       ; 61
    95dc:       de bf           out     0x3e, r29       ; 62

[more stuff]

  return( 0 ); /* When main() returns the .FINIsh function will be
called to put I/O in its lowest power state.  Probably the same as the
power up state */
}/* main() */
    9aec:       80 e0           ldi     r24, 0x00       ; 0
    9aee:       90 e0           ldi     r25, 0x00       ; 0
    9af0:       c5 5b           subi    r28, 0xB5       ; 181
    9af2:       df 4f           sbci    r29, 0xFF       ; 255
    9af4:       cd bf           out     0x3d, r28       ; 61
    9af6:       de bf           out     0x3e, r29       ; 62
    9af8:       08 95           ret

Did I miss anything in the documentation that would tell me not to use
auto variables in .initX sections after .init2 that sets the stack?