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/* Startup code for Nios II
Copyright (C) 1995-2019 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, see
<https://www.gnu.org/licenses/>. */
/* 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
The stack pointer, sp, will point to the argument count on the stack.
The initial state of the stack when a userspace process is started is:
Purpose Start Address Length
Unspecified High Addresses
Referenced strings, etc. Varies
Unspecified
Null auxilliary vector entry 4bytes
Auxilliary vector entries 8bytes each
NULL terminator for envp 4bytes
Environment pointers sp+8+4*argc 4bytes each
NULL terminator for argv sp+4+4*argc 4bytes
Argument pointers sp+4 4bytes each
Argument count sp 4bytes
Unspecified Low Addresses
If the application should register a destructor function with atexit,
the pointer will be placed in r4. Otherwise r4 will be zero.
The contents of all other registers are unspecified. User code should
set fp to zero to mark the end of the frame chain.
The auxilliary vector is a series of pairs of 32-bit tag and 32-bit
value, terminated by an AT_NULL tag.
*/
.text
.globl _start
.type _start,%function
_start:
/* Set up the global pointer. */
movhi gp, %hiadj(_gp)
addi gp, gp, %lo(_gp)
/* Save the stack pointer. */
mov r2, sp
/* Create room on the stack for the fini, rtld_fini and stack_end args
to __libc_start_main. */
subi sp, sp, 12
/* Push stack_end */
stw r2, 8(sp)
/* Push rtld_fini */
stw r4, 4(sp)
/* Set up the GOT pointer. */
nextpc r22
1: movhi r2, %hiadj(_gp_got - 1b)
addi r2, r2, %lo(_gp_got - 1b)
add r22, r22, r2
/* Push fini */
movhi r8, %call_hiadj(__libc_csu_fini)
addi r8, r8, %call_lo(__libc_csu_fini)
add r8, r8, r22
ldw r8, 0(r8)
stw r8, 0(sp)
/* r7 == init */
movhi r7, %call_hiadj(__libc_csu_init)
addi r7, r7, %call_lo(__libc_csu_init)
add r7, r7, r22
ldw r7, 0(r7)
/* r6 == argv */
addi r6, sp, 16
/* r5 == argc */
ldw r5, 12(sp)
/* r4 == main */
movhi r4, %call_hiadj(main)
addi r4, r4, %call_lo(main)
add r4, r4, r22
ldw r4, 0(r4)
/* fp == 0 */
mov fp, zero
/* __libc_start_main (main, argc, argv, init, fini, rtld_fini,
stack_end) */
/* Let the libc call main and exit with its return code. */
movhi r2, %call_hiadj(__libc_start_main)
addi r2, r2, %call_lo(__libc_start_main)
add r2, r2, r22
ldw r2, 0(r2)
callr r2
/* should never get here....*/
movhi r2, %call_hiadj(abort)
addi r2, r2, %call_lo(abort)
add r2, r2, r22
ldw r2, 0(r2)
callr r2
/* 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
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