start.s

glibc 库, 不仅可以学习使用库函数,还可以学习函数的具体实现,是提高功力的好资料

/* Startup code for programs linked with GNU libc.  PowerPC64 version.
   Copyright (C) 1998,1999,2000,2001,2002,2003 Free Software Foundation, Inc.
   This file is part of the GNU C Library.

   The GNU C Library is free software; you can redistribute it and/or
   modify it under the terms of the GNU Lesser General Public
   License as published by the Free Software Foundation; either
   version 2.1 of the License, or (at your option) any later version.

   In addition to the permissions in the GNU Lesser General Public
   License, the Free Software Foundation gives you unlimited
   permission to link the compiled version of this file with other
   programs, and to distribute those programs without any restriction
   coming from the use of this file. (The GNU Lesser General Public
   License restrictions do apply in other respects; for example, they
   cover modification of the file, and distribution when not linked
   into another program.)

   Note that people who make modified versions of this file are not
   obligated to grant this special exception for their modified
   versions; it is their choice whether to do so. The GNU Lesser
   General Public License gives permission to release a modified
   version without this exception; this exception also makes it
   possible to release a modified version which carries forward this
   exception.

   The GNU C Library is distributed in the hope that it will be useful,
   but WITHOUT ANY WARRANTY; without even the implied warranty of
   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
   Lesser General Public License for more details.

   You should have received a copy of the GNU Lesser General Public
   License along with the GNU C Library; if not, write to the Free
   Software Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA
   02111-1307 USA.  */

#include <sysdep.h>
#include "bp-sym.h"

 /* These are the various addresses we require.  */
#ifdef PIC
	.section ".data.rel.ro.local","aw"
#else
	.section ".rodata"
#endif
	.align	3
L(start_addresses):
	.quad	0 /* was _SDA_BASE_  but not in 64-bit ABI*/
/*     function descriptors so don't need JUMPTARGET */
	.quad	BP_SYM(main)
	.quad 	__libc_csu_init
	.quad 	__libc_csu_fini

	ASM_SIZE_DIRECTIVE(L(start_addresses))

	.section	".toc","aw"
.L01:
	.tc	L(start_addresses)[TC],L(start_addresses)
	.section ".text"
ENTRY(_start)
 /* Save the stack pointer, in case we're statically linked under Linux.  */
	mr	r9,r1
 /* Set up an initial stack frame, and clear the LR.  */
	clrrdi	r1,r1,4
	li	r0,0
	stdu	r1,-128(r1)
	mtlr	r0
	std	r0,0(r1)

 /* put the address of start_addresses in r8...  **
** PPC64 ABI uses R13 for thread local, so we leave it alone */
	ld	r8,.L01(r2)

 /* and continue in libc-start, in glibc.  */
	b	JUMPTARGET(BP_SYM(__libc_start_main))
/* The linker needs this nop to recognize that it's OK to call via a
   TOC adjusting stub.  */
	nop

END(_start)

/* Define a symbol for the first piece of initialized data.  */
	.section ".data"
	.globl	__data_start
__data_start:
weak_alias (__data_start, data_start)