xref: /freebsd/libexec/rtld-elf/powerpc/rtld_start.S (revision 9336e0699bda8a301cd2bfa37106b6ec5e32012e)
1/*      $NetBSD: rtld_start.S,v 1.4 2001/09/26 04:06:43 mycroft Exp $   */
2
3/*-
4 * Copyright (C) 1998   Tsubai Masanari
5 * All rights reserved.
6 *
7 * Redistribution and use in source and binary forms, with or without
8 * modification, are permitted provided that the following conditions
9 * are met:
10 * 1. Redistributions of source code must retain the above copyright
11 *    notice, this list of conditions and the following disclaimer.
12 * 2. Redistributions in binary form must reproduce the above copyright
13 *    notice, this list of conditions and the following disclaimer in the
14 *    documentation and/or other materials provided with the distribution.
15 * 3. The name of the author may not be used to endorse or promote products
16 *    derived from this software without specific prior written permission.
17 *
18 * THIS SOFTWARE IS PROVIDED BY THE AUTHOR ``AS IS'' AND ANY EXPRESS OR
19 * IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES
20 * OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED.
21 * IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR ANY DIRECT, INDIRECT,
22 * INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT
23 * NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
24 * DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
25 * THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
26 * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
27 * OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
28 *
29 * $FreeBSD$
30 */
31
32#include <machine/asm.h>
33
34.extern _GLOBAL_OFFSET_TABLE_
35.extern _DYNAMIC
36
37_ENTRY(.rtld_start)
38	stwu    %r1,-48(%r1)	/* 16-byte aligned stack for reg saves +
39				exit_proc & obj _rtld args +
40				backchain & lrsave stack frame */
41	stw     %r3,16(%r1)	/*  argc */
42	stw     %r4,20(%r1)	/*  argv */
43	stw     %r5,24(%r1)	/*  envp */
44/*	stw     %r6,28(%r1)   *//*  obj (always 0) */
45/*	stw     %r7,32(%r1)   *//*  cleanup (always 0) */
46	stw     %r8,36(%r1)	/*  ps_strings */
47
48	/*
49	 * Perform initial relocation of ld-elf.so. Not as easy as it
50	 * sounds.
51	 *  - perform small forward branch to put PC into link reg
52	 *  - use link-time constants to determine offset to the
53	 *    _DYNAMIC section and the GOT. Add these to the PC to
54	 *    convert to absolute addresses.
55	 *  - sync icache to allow execution of the SVR4 ABI-specified
56	 *    blrl instruction preceding the GOT
57	 *  - Use this instruction to determine the GOT absolute address
58	 *  - read GOT[0], which is the SVR4 ABI-specified link-time
59	 *    value of _DYNAMIC. Subtract this value from the absolute
60	 *    value to determine the load address
61	 *  - call reloc_non_plt_self() to fix up ld-elf.so's relocations
62	 */
63	bl	1f
64	.long	_DYNAMIC-.
65	.long	_GLOBAL_OFFSET_TABLE_-.	/* branch lr + 4 */
661:
67	mflr	%r3		/* PC value at .long */
68	lwz	%r4,4(%r3)
69	add	%r4,%r4,%r3	/* &_GLOBAL_OFFSET_TABLE-4, blrl insn. */
70	dcbst   %r0,%r4         /* sync i-cache with d-cache */
71	sync
72	icbi    %r0,%r4
73	isync
74
75	lwz	%r4,0(%r3)	/* offset to _DYNAMIC */
76	add	%r3,%r4,%r3	/* r3 = &_DYNAMIC, absolute value */
77
78	bl	_GLOBAL_OFFSET_TABLE_@local-4
79	mflr	%r4		/* &_GLOBAL_OFFSET_TABLE_, absolute value */
80	lwz	%r4,0(%r4)	/* linker &_DYNAMIC, from got[0] */
81	subf	%r4,%r4,%r3	/* subtract to calculate relocbase */
82
83	bl	reloc_non_plt_self@plt /* reloc_non_plt_self(&_DYNAMIC,base) */
84
85	/*
86	 * The _rtld() function likes to see a stack layout containing
87	 * { argc, argv[0], argv[1] ... argv[N], 0, env[0], ... , env[N] }
88	 * Since the PowerPC stack was 16-byte aligned at exec time, the
89	 * original stack layout has to be found by moving back a word
90	 * from the argv pointer.
91	 */
92        lwz     %r4,20(%r1)	/* restore argv */
93        addi    %r3,%r4,-4	/* locate argc ptr, &argv[-1] */
94
95	addi	%r4,%r1,8	/* &exit_proc on stack */
96	addi	%r5,%r1,12	/* &obj_main on stack */
97
98	bl      _rtld@plt	/* &_start = _rtld(sp, &exit_proc, &obj_main)*/
99	mtlr    %r3
100
101	/*
102	 * Restore args, with new obj/exit proc
103	 */
104	lwz     %r3,16(%r1)     /* argc */
105	lwz     %r4,20(%r1)	/* argv */
106	lwz     %r5,24(%r1)	/* envp */
107	lwz     %r6,12(%r1)	/* obj */
108	lwz     %r7,8(%r1)	/* exit proc */
109	lwz     %r8,36(%r1)	/* ps_strings */
110        addi    %r1,%r1,48	/* restore original stackptr */
111
112	blrl	/* _start(argc, argv, envp, obj, cleanup, ps_strings) */
113
114	li      %r0,1		/* _exit() */
115	sc
116
117/*
118 * _rtld_bind_start()
119 *
120 * Call into the MI binder. This routine is reached via the PLT call cell,
121 * and then _rtld_powerpc_pltresolve().
122 * On entry, %r11 contains the index of the PLT cell, and %r12 contains
123 * a pointer to the ELF object for the file.
124 *  Save all registers, call into the binder to resolve and fixup the external
125 * routine, and then transfer to the external routine on return.
126 */
127	.globl  _rtld_bind
128
129_ENTRY(_rtld_bind_start)
130	stwu    %r1,-160(%r1)		# stack space for 29 regs + r0/lr/cr
131	stw     %r0,20(%r1)		# save r0
132	mflr    %r0
133	stw     %r0,16(%r1)		# save lr
134	mfcr    %r0
135	stw     %r0,12(%r1)		# save cr
136	stmw    %r3,24(%r1)		# save r3-r31
137
138	mr      %r3,%r12		# obj
139	mulli   %r4,%r11,12		# rela index * sizeof(Elf_Rela)
140	bl      _rtld_bind@PLT		# target addr = _rtld_bind(obj, reloff)
141	mtctr   %r3			# move absolute target addr into ctr
142
143        lmw     %r3,24(%r1)		# restore r3-r31
144        lwz     %r0,12(%r1)		# restore cr
145        mtcr    %r0
146        lwz     %r0,16(%r1)		# restore lr
147        mtlr    %r0
148        lwz     %r0,20(%r1)		# restore r0
149
150        addi    %r1,%r1,160		# restore stack
151        bctr				# jump to target
152
153
154/*
155 * _rtld_powerpc_pltresolve()
156 *
157 *  This routine is copied into the latter part of the 72-byte reserved
158 * area at the start of the PLT. The absolute address of the _rtld_bind_start
159 * routine, and the ELF object for the loaded file, are inserted into
160 * the code by the reloc.c:init_pltgot() routine.
161 *  The first time an external routine is called, the PLT slot will
162 * set up %r11 to the offset of the slot, and will jump to this routine.
163 * The ELF object is shifted into %r11, and _rtld_bind_start is called
164 * to complete the binding.
165 */
166_ENTRY(_rtld_powerpc_pltresolve)
167        lis     %r12,0			# lis   12,_rtld_bind_start@ha
168        addi    %r12,%r12,0		# addi  12,12,_rtld_bind_start@l
169        mtctr   %r12
170        lis     %r12,0			# lis   12,obj@ha
171        addi    %r12,%r12,0		# addi  12,12,obj@l
172        bctr
173
174/*
175 * _rtld_powerpc_pltcall()
176 *
177 *  This routine is copied into the 72-byte reserved area at the
178 * start of the PLT. The reloc.c:init_pltgot() routine inserts
179 * the absolute address of the jumptable.
180 *  Control is transferred to this routine when the binder has
181 * located the external routine, but determined that it is > 32Mb
182 * from the PLT slot. Code is inserted into the PLT slot to set up
183 * %r11 with the jumptable index, and jump to here, where the
184 * absolute address of the external routine is loaded from the
185 * jumptable and transferred to
186 */
187_ENTRY(_rtld_powerpc_pltcall)
188        slwi    %r11,%r11,2		# jmptab offset = index * 4
189        addis   %r11,%r11,0		# addis 11,11,jmptab@ha
190        lwz     %r11,0(%r11)		# lwz   11,jmptab@l(11)
191        mtctr   %r11
192        bctr				# (*jmptab[index])()
193
194
195