1 /* Startup code compliant to the ELF s390 ABI.
2 Copyright (C) 2000, 2001, 2002, 2003, 2004, 2006
3 Free Software Foundation, Inc.
4 Contributed by Martin Schwidefsky (schwidefsky@de.ibm.com).
5 This file is part of the GNU C Library.
7 The GNU C Library is free software; you can redistribute it and/or
8 modify it under the terms of the GNU Lesser General Public
9 License as published by the Free Software Foundation; either
10 version 2.1 of the License, or (at your option) any later version.
12 In addition to the permissions in the GNU Lesser General Public
13 License, the Free Software Foundation gives you unlimited
14 permission to link the compiled version of this file with other
15 programs, and to distribute those programs without any restriction
16 coming from the use of this file. (The GNU Lesser General Public
17 License restrictions do apply in other respects; for example, they
18 cover modification of the file, and distribution when not linked
19 into another program.)
21 Note that people who make modified versions of this file are not
22 obligated to grant this special exception for their modified
23 versions; it is their choice whether to do so. The GNU Lesser
24 General Public License gives permission to release a modified
25 version without this exception; this exception also makes it
26 possible to release a modified version which carries forward this
29 The GNU C Library is distributed in the hope that it will be useful,
30 but WITHOUT ANY WARRANTY; without even the implied warranty of
31 MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
32 Lesser General Public License for more details.
34 You should have received a copy of the GNU Lesser General Public
35 License along with the GNU C Library; if not, write to the Free
36 Software Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA
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
62 /* Check if the kernel provides highgprs facility if needed by
66 la %r6,4(%r6) /* Skip the argument counter. */
68 .L11: l %r5,0(%r6) /* Skip the argument vector. */
73 .L12: l %r5,0(%r6) /* Skip the environment vector. */
78 /* Obtain the needed values from the auxiliary vector. */
80 lhi %r7,16 /* AT_HWCAP */
81 lhi %r8,3 /* AT_PHDR */
82 lhi %r9,5 /* AT_PHNUM */
83 lhi %r2,4 /* AT_PHENT */
87 l %r10,4(%r6) /* r10 = AT_HWCAP value. */
90 l %r11,4(%r6) /* r11 = AT_PHDR value. */
93 l %r12,4(%r6) /* r12 = AT_PHNUM value. */
96 l %r0,4(%r6) /* r0 = AT_PHENT value. */
101 /* Locate the ELF header by looking for the first PT_LOAD
102 segment with a p_offset of zero. */
104 lr %r4,%r11 /* Backup AT_PHDR. */
105 lhi %r7,1 /* PT_LOAD id */
107 .L19: cl %r7,0(%r4) /* p_type == PT_LOAD? */
109 cl %r8,4(%r4) /* p_offset == 0? */
111 l %r9,8(%r4) /* r9 = p_vaddr <- ELF header address */
113 .L20: alr %r4,%r0 /* r4 += AT_PHENT value */
116 j .+2 /* Trap, there must be such a phdr. */
118 .L24: lr %r4,%r11 /* Backup AT_PHDR. */
119 lhi %r2,6 /* PT_PHDR id */
122 l %r3,8(%r4) /* r3 = PT_PHDR p_vaddr */
124 .L22: alr %r4,%r0 /* r4 += AT_PHENT value */
127 ltr %r9,%r9 /* Load address == 0? */
128 jz .L14 /* No checking for PIE without PT_PHDR. */
131 .L25: clr %r3,%r11 /* PT_PHDR p_vaddr == AT_PHDR? */
134 slr %r9,%r3 /* elf_header_addr = AT_PHDR - PT_PHDR.p_vaddr */
136 .L21: l %r5,36(%r9) /* Load the e_flags field. */
138 jz .L14 /* Binary does not require highgprs facility. */
140 tml %r10,512 /* Check the AT_HWCAP value. */
141 jz 2 /* Trap if no highgprs facility available. */
144 /* Setup pointer to literal pool of _start */
146 .L0: ahi %r13,.Llit-.L0
148 /* load argc and argv from stack */
149 la %r4,4(%r15) # get argv
150 l %r3,0(%r15) # get argc
152 /* align the stack to a double word boundary */
156 /* Setup a stack frame and a parameter area */
157 ahi %r15,-104 # make room on stack
158 xc 0(4,%r15),0(%r15) # clear back-chain
160 /* set up arguments for __libc_start_main:
161 main, argc, argv, envp, _init, _fini, rtld_fini, stack_end
162 Note that envp will be determined later in __libc_start_main
164 stm %r14,%r15,96(%r15) # store rtld_fini/stack_end to parameter area
166 l %r6,.L2-.Llit(%r13) # load pointer to __libc_csu_fini
167 l %r5,.L1-.Llit(%r13) # load pointer to __libc_csu_init
168 l %r2,.L3-.Llit(%r13) # load pointer to main
169 l %r1,.L4-.Llit(%r13) # load pointer to __libc_start_main
171 l %r12,.L5-.Llit(%r13) # load .got pointer
179 /* ok, now branch to the libc main routine */
182 /* crash if __libc_start_main returns */
187 .L1: .long __libc_csu_init
188 .L2: .long __libc_csu_fini
190 .L4: .long __libc_start_main
192 .L1: .long __libc_csu_init-.Llit
193 .L2: .long __libc_csu_fini-.Llit
195 .L4: .long __libc_start_main@plt-.Llit
196 .L5: .long _GLOBAL_OFFSET_TABLE_-.Llit
199 /* Define a symbol for the first piece of initialized data. */
205 data_start = __data_start