1
/* Copyright (C) 2011 Free Software Foundation, Inc.
2
This file is part of the GNU C Library.
3
Contributed by Chris Metcalf <cmetcalf@tilera.com>, 2011.
5
The GNU C Library is free software; you can redistribute it and/or
6
modify it under the terms of the GNU Lesser General Public
7
License as published by the Free Software Foundation; either
8
version 2.1 of the License, or (at your option) any later version.
10
In addition to the permissions in the GNU Lesser General Public
11
License, the Free Software Foundation gives you unlimited
12
permission to link the compiled version of this file with other
13
programs, and to distribute those programs without any restriction
14
coming from the use of this file. (The GNU Lesser General Public
15
License restrictions do apply in other respects; for example, they
16
cover modification of the file, and distribution when not linked
17
into another program.)
19
Note that people who make modified versions of this file are not
20
obligated to grant this special exception for their modified
21
versions; it is their choice whether to do so. The GNU Lesser
22
General Public License gives permission to release a modified
23
version without this exception; this exception also makes it
24
possible to release a modified version which carries forward this
27
The GNU C Library is distributed in the hope that it will be useful,
28
but WITHOUT ANY WARRANTY; without even the implied warranty of
29
MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
30
Lesser General Public License for more details.
32
You should have received a copy of the GNU Lesser General Public
33
License along with the GNU C Library; if not, write to the Free
34
Software Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA
37
/* This is the canonical entry point, usually the first thing in the text
38
segment. The ELF standard tells us that the stack is set up like this on
39
entry (the left side is the offset from "sp"), in units of
40
__SIZEOF_POINTER__ entries:
51
The ElfInfo is pairs of key/value long words following the envp
52
pointers and terminated by a zero-valued key.
54
Although not mandated by the standard, it happens to be the case
55
that we store the actual argv and envp strings immediately after
56
the ElfInfo data on the stack.
58
On entry r0 points to the shared library termination function, or 0
68
.type _start,@function
71
/* Linux starts us with sp pointing at the conventional Elf layout,
72
but we need to allow two "caller" words for our ABI convention. */
74
/* Load argc (stored as a "long", equivalent to a pointer type). */
77
/* Save incoming 'sp', which points to the Elf argument block. */
82
/* Allocate stack frame callee space for __libc_start_main. */
83
ADDI_PTR r12, sp, -(2 * REGSIZE)
90
/* sp is not necessarily properly aligned on startup because
91
of the way ld.so pops off leading argv elements. So align it. */
97
/* Pass the address of the shared library termination function. */
100
/* Compute location where __libc_start_main's caller is supposed to
101
store its frame pointer. */
102
ADDI_PTR r12, sp, REGSIZE
104
/* Zero out callee space for return address. Unnecessary but free.
105
This is just paranoia to help backtracing not go awry. */
109
/* Zero out our frame pointer for __libc_start_main. */
112
/* Zero out lr to make __libc_start_main the end of backtrace. */
115
/* Compute a pointer to argv. envp will be determined
116
later in __libc_start_main. We set up the first argument
117
(the address of main) below. */
118
ADDI_PTR r2, r52, __SIZEOF_POINTER__
121
/* Pass the highest stack address to user code. */
122
ADDI_PTR r6, sp, (2 * REGSIZE)
124
/* Pass address of main() in r0, and of our own entry
125
points to .fini and .init in r3 and r4. */
127
moveli r0, hw2_last(main - .Lmy_pc)
130
moveli r3, hw2_last(__libc_csu_init - .Lmy_pc)
131
shl16insli r0, r0, hw1(main - .Lmy_pc)
134
shl16insli r3, r3, hw1(__libc_csu_init - .Lmy_pc)
135
shl16insli r0, r0, hw0(main - .Lmy_pc)
138
shl16insli r3, r3, hw0(__libc_csu_init - .Lmy_pc)
139
moveli r4, hw2_last(__libc_csu_fini - .Lmy_pc)
143
shl16insli r4, r4, hw1(__libc_csu_fini - .Lmy_pc)
147
shl16insli r4, r4, hw0(__libc_csu_fini - .Lmy_pc)
152
addli r0, r13, lo16(main - .Lmy_pc)
155
auli r0, r0, ha16(main - .Lmy_pc)
156
addli r3, r13, lo16(__libc_csu_init - .Lmy_pc)
159
auli r3, r3, ha16(__libc_csu_init - .Lmy_pc)
160
addli r4, r13, lo16(__libc_csu_fini - .Lmy_pc)
163
auli r4, r4, ha16(__libc_csu_fini - .Lmy_pc)
167
/* Call the user's main function, and exit with its value.
168
But let the libc call main. */
169
j plt(__libc_start_main)
172
/* Tell backtracer to give up (_start has no caller). */
173
info INFO_OP_CANNOT_BACKTRACE
175
.size _start, .-_start
177
/* Define a symbol for the first piece of initialized data. */
184
data_start = __data_start