1 /* Startup code compliant to the ELF x86-64 ABI.
2 Copyright (C) 2001, 2002, 2003, 2005 Free Software Foundation, Inc.
3 This file is part of the GNU C Library.
4 Contributed by Andreas Jaeger <aj@suse.de>, 2001.
6 The GNU C Library is free software; you can redistribute it and/or
7 modify it under the terms of the GNU Lesser General Public
8 License as published by the Free Software Foundation; either
9 version 2.1 of the License, or (at your option) any later version.
11 In addition to the permissions in the GNU Lesser General Public
12 License, the Free Software Foundation gives you unlimited
13 permission to link the compiled version of this file with other
14 programs, and to distribute those programs without any restriction
15 coming from the use of this file. (The GNU Lesser General Public
16 License restrictions do apply in other respects; for example, they
17 cover modification of the file, and distribution when not linked
18 into another program.)
20 Note that people who make modified versions of this file are not
21 obligated to grant this special exception for their modified
22 versions; it is their choice whether to do so. The GNU Lesser
23 General Public License gives permission to release a modified
24 version without this exception; this exception also makes it
25 possible to release a modified version which carries forward this
28 The GNU C Library is distributed in the hope that it will be useful,
29 but WITHOUT ANY WARRANTY; without even the implied warranty of
30 MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
31 Lesser General Public License for more details.
33 You should have received a copy of the GNU Lesser General Public
34 License along with the GNU C Library; if not, see
35 <http://www.gnu.org/licenses/>. */
37 /* Originally based on glibc's sysdeps/x86_64/elf/start.S */
39 /* This is the canonical entry point, usually the first thing in the text
40 segment. The SVR4/i386 ABI (pages 3-31, 3-32) says that when the entry
41 point runs, most registers' values are unspecified, except for:
43 %rdx Contains a function pointer to be registered with `atexit'.
44 This is how the dynamic linker arranges to have DT_FINI
45 functions called for shared libraries that have been loaded
46 before this code runs.
48 %rsp The stack contains the arguments and environment:
53 (8*(argc+1))(%rsp) envp[0]
57 #if defined NOT_IN_libc
58 # error error in build framework
64 .type _start,%function
65 #if defined(__UCLIBC_CTOR_DTOR__)
72 .type __uClibc_main,%function
73 /* Stick in a dummy reference to main(), so that if an application
74 * is linking when the main() function is in a static library (.a)
75 * we can be sure that main() actually gets linked in */
79 /* Clear the frame pointer. The ABI suggests this be done, to mark
80 the outermost frame obviously. */
83 /* Extract the arguments as encoded on the stack and set up
84 the arguments for __libc_start_main (int (*main) (int, char **, char **),
86 void (*init) (void), void (*fini) (void),
87 void (*rtld_fini) (void), void *stack_end).
88 The arguments are passed via registers and on the stack:
97 movq %rdx, %r9 /* Address of the shared library termination function. */
98 popq %rsi /* Pop the argument count. */
99 movq %rsp, %rdx /* argv starts just at the current stack top. */
101 /* Align the stack to a 16 byte boundary to follow the ABI. */
104 pushq %rax /* Push garbage because we push 8 more bytes. */
106 /* Provide the highest stack address to the user code (for stacks
107 which grow downwards). */
111 /* Give address for main() */
112 movq main@GOTPCREL(%rip), %rdi
114 /* setup init/fini address */
115 movq _init@GOTPCREL(%rip), %rcx
116 movq _fini@GOTPCREL(%rip), %r8
119 call __uClibc_main@PLT
121 /* Give address for main() */
124 /* setup init/fini address */
132 hlt /* Crash if somehow `exit' does return. */
133 .size _start,.-_start
135 /* Define a symbol for the first piece of initialized data. */
141 data_start = __data_start