1 /* Startup code compliant to the ELF s390 ABI.
2 Copyright (C) 2000-2015 Free Software Foundation, Inc.
3 Contributed by Martin Schwidefsky (schwidefsky@de.ibm.com).
4 This file is part of the GNU C Library.
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/>. */
38 This is the canonical entry point, usually the first thing in the text
39 segment. Most registers' values are unspecified, except for:
41 %r14 Contains a function pointer to be registered with `atexit'.
42 This is how the dynamic linker arranges to have DT_FINI
43 functions called for shared libraries that have been loaded
44 before this code runs.
46 %r15 The stack contains the arguments and environment:
51 (4*(argc+1))(%r15) envp[0]
58 .type _start,@function
60 /* Check if the kernel provides highgprs facility if needed by
64 la %r6,4(%r6) /* Skip the argument counter. */
66 .L11: l %r5,0(%r6) /* Skip the argument vector. */
71 .L12: l %r5,0(%r6) /* Skip the environment vector. */
76 /* Usually the auxiliary vector can be expected directly after
77 the environment variables. But we have to skip extra zeros
78 because the loader might have removed unsecure variables for
88 /* Obtain the needed values from the auxiliary vector. */
90 lhi %r7,16 /* AT_HWCAP */
91 lhi %r8,3 /* AT_PHDR */
92 lhi %r9,5 /* AT_PHNUM */
93 lhi %r2,4 /* AT_PHENT */
97 l %r10,4(%r6) /* r10 = AT_HWCAP value. */
100 l %r11,4(%r6) /* r11 = AT_PHDR value. */
103 l %r12,4(%r6) /* r12 = AT_PHNUM value. */
106 l %r0,4(%r6) /* r0 = AT_PHENT value. */
111 /* Locate the ELF header by looking for the first PT_LOAD
112 segment with a p_offset of zero. */
114 lr %r4,%r11 /* Backup AT_PHDR. */
115 lhi %r7,1 /* PT_LOAD id */
117 .L19: cl %r7,0(%r4) /* p_type == PT_LOAD? */
119 cl %r8,4(%r4) /* p_offset == 0? */
121 l %r9,8(%r4) /* r9 = PT_LOAD.p_vaddr <- ELF header address */
123 .L20: alr %r4,%r0 /* r4 += AT_PHENT value */
126 j .+2 /* Trap, there must be such a phdr. */
128 .L24: lr %r4,%r11 /* Backup AT_PHDR. */
129 lhi %r2,6 /* PT_PHDR id */
132 l %r3,8(%r4) /* r3 = PT_PHDR p_vaddr */
134 .L22: alr %r4,%r0 /* r4 += AT_PHENT value */
137 j .L14 /* No PT_PHDR found - skip checking. */
139 .L25: slr %r11,%r3 /* AT_PHDR - PT_PHDR.p_vaddr (relocation offset)*/
140 alr %r9,%r11 /* PT_LOAD.p_vaddr += relocation offset */
142 l %r5,36(%r9) /* Load the e_flags field. */
144 jz .L14 /* Binary does not require highgprs facility. */
146 tml %r10,512 /* Check the AT_HWCAP value. */
147 jz 2 /* Trap if no highgprs facility available. */
150 /* Setup pointer to literal pool of _start */
152 .L0: ahi %r13,.Llit-.L0
154 /* load argc and argv from stack */
155 la %r4,4(%r15) # get argv
156 l %r3,0(%r15) # get argc
158 /* align the stack to a double word boundary */
162 /* Setup a stack frame and a parameter area */
163 ahi %r15,-104 # make room on stack
164 xc 0(4,%r15),0(%r15) # clear back-chain
166 /* set up arguments for __libc_start_main:
167 main, argc, argv, envp, _init, _fini, rtld_fini, stack_end
168 Note that envp will be determined later in __libc_start_main
170 stm %r14,%r15,96(%r15) # store rtld_fini/stack_end to parameter area
172 l %r6,.L2-.Llit(%r13) # load pointer to __libc_csu_fini
173 l %r5,.L1-.Llit(%r13) # load pointer to __libc_csu_init
174 l %r2,.L3-.Llit(%r13) # load pointer to main
175 l %r1,.L4-.Llit(%r13) # load pointer to __libc_start_main
177 l %r12,.L5-.Llit(%r13) # load .got pointer
185 /* ok, now branch to the libc main routine */
188 /* crash if __libc_start_main returns */
193 .L1: .long __libc_csu_init
194 .L2: .long __libc_csu_fini
196 .L4: .long __libc_start_main
198 .L1: .long __libc_csu_init-.Llit
199 .L2: .long __libc_csu_fini-.Llit
201 .L4: .long __libc_start_main@plt-.Llit
202 .L5: .long _GLOBAL_OFFSET_TABLE_-.Llit
205 /* Define a symbol for the first piece of initialized data. */
211 data_start = __data_start