1 /* Startup code compliant to the ELF s390 ABI.
2 Copyright (C) 2000-2023 Free Software Foundation, Inc.
3 This file is part of the GNU C Library.
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, see
34 <https://www.gnu.org/licenses/>. */
39 This is the canonical entry point, usually the first thing in the text
40 segment. Most registers' values are unspecified, except for:
42 %r14 Contains a function pointer to be registered with `atexit'.
43 This is how the dynamic linker arranges to have DT_FINI
44 functions called for shared libraries that have been loaded
45 before this code runs.
47 %r15 The stack contains the arguments and environment:
52 (4*(argc+1))(%r15) envp[0]
59 .type _start,@function
62 /* Mark r14 as undefined in order to stop unwinding here! */
65 /* Check if the kernel provides highgprs facility if needed by
69 la %r6,4(%r6) /* Skip the argument counter. */
71 .L11: l %r5,0(%r6) /* Skip the argument vector. */
76 .L12: l %r5,0(%r6) /* Skip the environment vector. */
81 /* Usually the auxiliary vector can be expected directly after
82 the environment variables. But we have to skip extra zeros
83 because the loader might have removed unsecure variables for
93 /* Obtain the needed values from the auxiliary vector. */
95 lhi %r7,16 /* AT_HWCAP */
96 lhi %r8,3 /* AT_PHDR */
97 lhi %r9,5 /* AT_PHNUM */
98 lhi %r2,4 /* AT_PHENT */
102 l %r10,4(%r6) /* r10 = AT_HWCAP value. */
105 l %r11,4(%r6) /* r11 = AT_PHDR value. */
108 l %r12,4(%r6) /* r12 = AT_PHNUM value. */
111 l %r0,4(%r6) /* r0 = AT_PHENT value. */
116 /* Locate the ELF header by looking for the first PT_LOAD
117 segment with a p_offset of zero. */
119 lr %r4,%r11 /* Backup AT_PHDR. */
120 lhi %r7,1 /* PT_LOAD id */
122 .L19: cl %r7,0(%r4) /* p_type == PT_LOAD? */
124 cl %r8,4(%r4) /* p_offset == 0? */
126 l %r9,8(%r4) /* r9 = PT_LOAD.p_vaddr <- ELF header address */
128 .L20: alr %r4,%r0 /* r4 += AT_PHENT value */
131 j .+2 /* Trap, there must be such a phdr. */
133 .L24: lr %r4,%r11 /* Backup AT_PHDR. */
134 lhi %r2,6 /* PT_PHDR id */
137 l %r3,8(%r4) /* r3 = PT_PHDR p_vaddr */
139 .L22: alr %r4,%r0 /* r4 += AT_PHENT value */
142 j .L14 /* No PT_PHDR found - skip checking. */
144 .L25: slr %r11,%r3 /* AT_PHDR - PT_PHDR.p_vaddr (relocation offset)*/
145 alr %r9,%r11 /* PT_LOAD.p_vaddr += relocation offset */
147 l %r5,36(%r9) /* Load the e_flags field. */
149 jz .L14 /* Binary does not require highgprs facility. */
151 tml %r10,512 /* Check the AT_HWCAP value. */
152 jz 2 /* Trap if no highgprs facility available. */
155 /* Setup pointer to literal pool of _start */
157 .L0: ahi %r13,.Llit-.L0
159 /* load argc and argv from stack */
160 la %r4,4(%r15) # get argv
161 l %r3,0(%r15) # get argc
163 /* align the stack to a double word boundary */
167 /* Setup a stack frame and a parameter area */
168 ahi %r15,-104 # make room on stack
169 xc 0(4,%r15),0(%r15) # clear back-chain
171 /* set up arguments for __libc_start_main:
172 main, argc, argv, envp, _init, _fini, rtld_fini, stack_end
173 Note that envp will be determined later in __libc_start_main
175 stm %r14,%r15,96(%r15) # store rtld_fini/stack_end to parameter area
177 l %r2,.L3-.Llit(%r13) # load pointer to main
178 l %r1,.L4-.Llit(%r13) # load pointer to __libc_start_main
180 l %r12,.L5-.Llit(%r13) # load .got pointer
185 lhi %r6, 0 # Used to fini.
186 lhi %r5, 0 # Used to init.
188 /* ok, now branch to the libc main routine */
191 /* crash if __libc_start_main returns */
198 .L4: .long __libc_start_main
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