1 /* Startup code compliant to the ELF s390 ABI.
2 Copyright (C) 2000-2018 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/>. */
40 This is the canonical entry point, usually the first thing in the text
41 segment. Most registers' values are unspecified, except for:
43 %r14 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 %r15 The stack contains the arguments and environment:
53 (4*(argc+1))(%r15) envp[0]
60 .type _start,@function
63 /* Mark r14 as undefined in order to stop unwinding here! */
66 /* Check if the kernel provides highgprs facility if needed by
70 la %r6,4(%r6) /* Skip the argument counter. */
72 .L11: l %r5,0(%r6) /* Skip the argument vector. */
77 .L12: l %r5,0(%r6) /* Skip the environment vector. */
82 /* Usually the auxiliary vector can be expected directly after
83 the environment variables. But we have to skip extra zeros
84 because the loader might have removed unsecure variables for
94 /* Obtain the needed values from the auxiliary vector. */
96 lhi %r7,16 /* AT_HWCAP */
97 lhi %r8,3 /* AT_PHDR */
98 lhi %r9,5 /* AT_PHNUM */
99 lhi %r2,4 /* AT_PHENT */
103 l %r10,4(%r6) /* r10 = AT_HWCAP value. */
106 l %r11,4(%r6) /* r11 = AT_PHDR value. */
109 l %r12,4(%r6) /* r12 = AT_PHNUM value. */
112 l %r0,4(%r6) /* r0 = AT_PHENT value. */
117 /* Locate the ELF header by looking for the first PT_LOAD
118 segment with a p_offset of zero. */
120 lr %r4,%r11 /* Backup AT_PHDR. */
121 lhi %r7,1 /* PT_LOAD id */
123 .L19: cl %r7,0(%r4) /* p_type == PT_LOAD? */
125 cl %r8,4(%r4) /* p_offset == 0? */
127 l %r9,8(%r4) /* r9 = PT_LOAD.p_vaddr <- ELF header address */
129 .L20: alr %r4,%r0 /* r4 += AT_PHENT value */
132 j .+2 /* Trap, there must be such a phdr. */
134 .L24: lr %r4,%r11 /* Backup AT_PHDR. */
135 lhi %r2,6 /* PT_PHDR id */
138 l %r3,8(%r4) /* r3 = PT_PHDR p_vaddr */
140 .L22: alr %r4,%r0 /* r4 += AT_PHENT value */
143 j .L14 /* No PT_PHDR found - skip checking. */
145 .L25: slr %r11,%r3 /* AT_PHDR - PT_PHDR.p_vaddr (relocation offset)*/
146 alr %r9,%r11 /* PT_LOAD.p_vaddr += relocation offset */
148 l %r5,36(%r9) /* Load the e_flags field. */
150 jz .L14 /* Binary does not require highgprs facility. */
152 tml %r10,512 /* Check the AT_HWCAP value. */
153 jz 2 /* Trap if no highgprs facility available. */
156 /* Setup pointer to literal pool of _start */
158 .L0: ahi %r13,.Llit-.L0
160 /* load argc and argv from stack */
161 la %r4,4(%r15) # get argv
162 l %r3,0(%r15) # get argc
164 /* align the stack to a double word boundary */
168 /* Setup a stack frame and a parameter area */
169 ahi %r15,-104 # make room on stack
170 xc 0(4,%r15),0(%r15) # clear back-chain
172 /* set up arguments for __libc_start_main:
173 main, argc, argv, envp, _init, _fini, rtld_fini, stack_end
174 Note that envp will be determined later in __libc_start_main
176 stm %r14,%r15,96(%r15) # store rtld_fini/stack_end to parameter area
178 l %r6,.L2-.Llit(%r13) # load pointer to __libc_csu_fini
179 l %r5,.L1-.Llit(%r13) # load pointer to __libc_csu_init
180 l %r2,.L3-.Llit(%r13) # load pointer to main
181 l %r1,.L4-.Llit(%r13) # load pointer to __libc_start_main
183 l %r12,.L5-.Llit(%r13) # load .got pointer
191 /* ok, now branch to the libc main routine */
194 /* crash if __libc_start_main returns */
200 .L1: .long __libc_csu_init
201 .L2: .long __libc_csu_fini
203 .L4: .long __libc_start_main
205 .L1: .long __libc_csu_init-.Llit
206 .L2: .long __libc_csu_fini-.Llit
208 .L4: .long __libc_start_main@plt-.Llit
209 .L5: .long _GLOBAL_OFFSET_TABLE_-.Llit
212 /* Define a symbol for the first piece of initialized data. */
218 data_start = __data_start