/* Startup code for ARM & ELF Copyright (C) 1995, 1996, 1997, 1998, 2001, 2002, 2005 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. */ /* This is the canonical entry point, usually the first thing in the text segment. Note that the code in the .init section has already been run. This includes _init and _libc_init At this entry point, most registers' values are unspecified, except: a1 Contains a function pointer to be registered with `atexit'. This is how the dynamic linker arranges to have DT_FINI functions called for shared libraries that have been loaded before this code runs. sp The stack contains the arguments and environment: 0(sp) argc 4(sp) argv[0] ... (4*argc)(sp) NULL (4*(argc+1))(sp) envp[0] ... NULL */ /* For uClinux it looks like this: argc argument counter (integer) argv char *argv[] envp char *envp[] argv[0] program name (pointer) argv[1...N] program args (pointers) argv[argc-1] end of args (integer) NULL env[0...N] environment variables (pointers) NULL ARM register quick reference: Name Number ARM Procedure Calling Standard Role a1 r0 argument 1 / integer result / scratch register / argc a2 r1 argument 2 / scratch register / argv a3 r2 argument 3 / scratch register / envp a4 r3 argument 4 / scratch register v1 r4 register variable v2 r5 register variable v3 r6 register variable v4 r7 register variable v5 r8 register variable sb/v6 r9 static base / register variable sl/v7 r10 stack limit / stack chunk handle / reg. variable fp r11 frame pointer ip r12 scratch register / new-sb in inter-link-unit calls sp r13 lower end of current stack frame lr r14 link address / scratch register pc r15 program counter */ #include <features.h> .text .globl _start .type _start,%function .type _init,%function .type _fini,%function #ifndef __UCLIBC_CTOR_DTOR__ .weak _init .weak _fini #endif _start: /* Clear the frame pointer and link register since this is the outermost frame. */ mov fp, #0 mov lr, #0 /* Pop argc off the stack and save a pointer to argv */ ldr a2, [sp], #4 mov a3, sp /* Push stack limit */ str a3, [sp, #-4]! /* Push rtld_fini */ str a1, [sp, #-4]! #ifdef __PIC__ ldr sl, .L_GOT .L_GOT_OFF: add sl, pc, sl ldr ip, .L_GOT+4 /* _fini */ ldr a1, [sl, ip] str a1, [sp, #-4]! /* Push _fini */ ldr ip, .L_GOT+8 /* _init */ ldr a4, [sl, ip] ldr ip, .L_GOT+12 /* main */ ldr a1, [sl, ip] /* __uClibc_main (main, argc, argv, init, fini, rtld_fini, stack_end) */ /* Let the libc call main and exit with its return code. */ b __uClibc_main(PLT) #else /* Fetch address of fini */ ldr ip, =_fini /* Push fini */ str ip, [sp, #-4]! /* Set up the other arguments in registers */ ldr a1, =main ldr a4, =_init /* __uClibc_main (main, argc, argv, init, fini, rtld_fini, stack_end) */ /* Let the libc call main and exit with its return code. */ b __uClibc_main #endif /* should never get here....*/ bl abort #ifdef __PIC__ .L_GOT: .word _GLOBAL_OFFSET_TABLE_-(.L_GOT_OFF+8) .word _fini(GOT) .word _init(GOT) .word main(GOT) #endif /* Define a symbol for the first piece of initialized data. */ .data .globl __data_start __data_start: .long 0 .weak data_start data_start = __data_start