Re: ARM crt.. files

[Richard Henderson <rth@cygnus.com>]

On Sun, Jun 28, 1998 at 05:09:55PM -0400, Roland McGrath wrote:
> I believe I have devised a solution, but I am too lazy to fully implement
> it myself.  This would replace my postprocessed-assembly kludge with a
> postprocessed-object file kludge, which is probably more portable given GNU
> binutils.  

An interesting idea.

> The objcopy step is necessary because ld will stick all the unmentioned
> sections into the output, and as far as I can tell there is no way to tell
> it on the command line or in a linker script to discard sections.

SECTIONS
{
  .init : { *(.init.prologue) }
  .fini : { *(.fini.prologue) }
  /DISCARD/ : { *(.init.epilogue) *(.fini.epilogue) *(.garbage) }
}

SECTIONS
{
  .init : { *(.init.epilogue) }
  .fini : { *(.fini.epilogue) }
  /DISCARD/ : { *(.init.prologue) *(.fini.prologue) *(.garbage) }
}

It is also necesary to strip the future crtn.o (ld -s) because 
the _init and _fini symbols will still be present even though
their defining section is removed (arguably a bug in ld).

I also recommend the following init-fini.c, where ALIGN_INIT_CODE
should come from some target header.  The align is necessary to 
get the assembler to insert the proper nops.  The change to
i_am_not_a_leaf prevents us from having to remove it from the
symbol table.


r~

extern void __gmon_start__ (void);
#pragma weak __gmon_start__

#define ALIGN_INIT_CODE ".align 5"

void __attribute__((section (".init.prologue")))
_init (void)
{
  /* We cannot use the normal constructor mechanism in gcrt1.o because it
     appears before crtbegin.o in the link, so the header elt of .ctors
     would come after the elt for __gmon_start__.  One approach is for
     gcrt1.o to reference a symbol which would be defined by some library
     module which has a constructor; but then user code's constructors
     would come first, and not be profiled.  */

  if (__gmon_start__)
    __gmon_start__ ();

  asm (ALIGN_INIT_CODE "\n.section .init.epilogue,\"ax\",@progbits");

  /* Now the epilog. */
}

void __attribute__((section (".fini.prologue")))
_fini (void)
{

  asm (ALIGN_INIT_CODE "\n.section .garbage,\"ax\",@progbits");
  /* End of the _fini prolog. */

  {
    /* Let GCC know that _fini is not a leaf function by having a dummy
       function call here.  We arrange for this call to be omitted from
       either crt file.  */
    void (*i_am_not_a_leaf)(void) = (void *)0x12345678;
    i_am_not_a_leaf ();
  }

  asm (".section .fini.epilogue,\"ax\",@progbits");
  /* Beginning of the _fini epilog. */
}