rtld_start.S revision 1.18
1 /* $NetBSD: rtld_start.S,v 1.18 2024/08/03 21:59:58 riastradh Exp $ */ 2 3 /*- 4 * Copyright (c) 2000 Eduardo Horvath. 5 * Copyright (c) 1999, 2002, 2003 The NetBSD Foundation, Inc. 6 * All rights reserved. 7 * 8 * This code is derived from software contributed to The NetBSD Foundation 9 * by Christos Zoulas, Paul Kranenburg and by Charles M. Hannum. 10 * 11 * Redistribution and use in source and binary forms, with or without 12 * modification, are permitted provided that the following conditions 13 * are met: 14 * 1. Redistributions of source code must retain the above copyright 15 * notice, this list of conditions and the following disclaimer. 16 * 2. Redistributions in binary form must reproduce the above copyright 17 * notice, this list of conditions and the following disclaimer in the 18 * documentation and/or other materials provided with the distribution. 19 * 20 * THIS SOFTWARE IS PROVIDED BY THE NETBSD FOUNDATION, INC. AND CONTRIBUTORS 21 * ``AS IS'' AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED 22 * TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR 23 * PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE FOUNDATION OR CONTRIBUTORS 24 * BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR 25 * CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF 26 * SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS 27 * INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN 28 * CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) 29 * ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE 30 * POSSIBILITY OF SUCH DAMAGE. 31 */ 32 33 #include <machine/asm.h> 34 #define _LOCORE 35 #include <machine/frame.h> 36 37 /* 38 * ELF: 39 * On startup the stack should contain 16 extended word register save area, 40 * followed by the arg count, etc. 41 * 42 * _rtld() expects the stack pointer to point to two longwords for argument 43 * return followed by argc, etc. We need to create a pointer to 44 * &argc + 16 and pass that in. The return args will be in those locations. 45 * 46 * NB: We are violating the ELF spec by passing a pointer to the ps strings in 47 * %g1 instead of a termination routine. 48 */ 49 50 .register %g2,#scratch 51 .register %g3,#scratch 52 53 /* Offset of ARGC from bottom of stack */ 54 #define ARGC 176 55 56 .section ".text" 57 .align 4 58 .global _rtld_start 59 .type _rtld_start,@function 60 _rtld_start: 61 mov 0, %fp /* Erect a fence post for ourselves */ 62 mov %g1, %l1 /* save ps_strings */ 63 sub %sp, 48+16, %sp /* Make room for return args */ 64 65 sethi %hi(_GLOBAL_OFFSET_TABLE_-4), %l7 66 call 0f 67 add %l7, %lo(_GLOBAL_OFFSET_TABLE_+4), %l7 68 call _DYNAMIC+8 69 0: add %l7, %o7, %l7 /* real &_GLOBAL_OFFSET_TABLE_ */ 70 ld [%o7+8], %o0 /* load stub call instruction */ 71 ldx [%l7], %l0 /* base-relative &_DYNAMIC */ 72 sll %o0, 2, %o0 /* extract PC offset */ 73 sra %o0, 0, %o0 /* sign-extend */ 74 75 add %o0, %o7, %o0 /* real &_DYNAMIC */ 76 sub %o0, %l0, %l0 /* relocbase */ 77 call _rtld_relocate_nonplt_self 78 mov %l0, %o1 /* relocbase */ 79 80 mov %l0, %o1 /* relocbase */ 81 call _rtld 82 add %sp, BIAS + ARGC, %o0 /* &argc - 16 */ 83 84 ldx [%sp + BIAS + ARGC], %g3 /* arg: cleanup */ 85 ldx [%sp + BIAS + ARGC + 8], %g2 /* arg: obj */ 86 add %sp, 48+16, %sp /* restore stack pointer */ 87 88 jmp %o0 89 mov %l1, %g1 /* restore ps_strings */ 90 91 92 /* 93 * We have two separate entry points to the runtime linker. 94 * I'm implementing this following the SPARC v9 ABI spec. 95 * 96 * _rtld_bind_start_0(y, x) is called from .PLT0, and is used for 97 * PLT entries above 32768. 98 * 99 * _rtld_bind_start_1(y, x) is called from .PLT1, and is used for 100 * PLT entries below 32768. 101 * 102 * The first two entries of PLT2 contain the xword object pointer. 103 * 104 * These routines are called with two longword arguments, 105 * x and y. To calculate the address of the entry, 106 * _rtld_bind_start_1(y, x) does: 107 * 108 * n = x >> 15; 109 * 110 * and _rtld_bind_start_0(y, x) does: 111 * 112 * i = x - y + 8 - 32768*32; 113 * n = 32768 + (i/5120)*160 + (i%5120)/24; 114 * 115 * Neither routine needs to issue a save since it's already been 116 * done in the PLT entry. 117 */ 118 119 .section ".text" 120 .align 4 121 .global _rtld_bind_start_0 122 .type _rtld_bind_start_0,@function 123 _rtld_bind_start_0: # (y, x) 124 /* %o0 = obj->pltgot[6] */ 125 /* %o1 = plt[4] */ 126 /* %o1 - %o0 + 8 == offset of plt[] from obj->pltgot[] */ 127 /* -32768*32 to get offset from beginning of upper PLT section */ 128 129 sethi %hi(32768*32-8), %l1 130 sub %o1, %o0, %l0 /* i = x - y */ 131 or %l1, %lo(32768*32-8), %l1 132 sub %l0, %l1, %l0 /* i = x - y + 8 - 32768*32 */ 133 134 ldx [%o0 + (10*4)], %o0 /* Load object pointer from PLT2 */ 135 136 sethi %hi(5120), %l1 137 sdivx %l0, %l1, %l1 /* Calculate i/5120 */ 138 sllx %l1, 2, %l2 139 add %l2, %l1, %l2 140 sllx %l2, 10, %l2 141 sub %l0, %l2, %l2 /* And i%5120 */ 142 143 /* Let the division churn for a bit. */ 144 sdivx %l2, 24, %l4 /* (i%5120)/24 */ 145 146 /* 160 is (32 * 5) or (32 * (4 + 1)) */ 147 sllx %l1, 2, %l3 /* 4 * (i/5120) */ 148 add %l1, %l3, %l3 /* 5 * (i/5120) */ 149 sllx %l3, 5, %l3 /* 32 * 5 * (i/5120) */ 150 151 sethi %hi(32768), %l6 152 add %l3, %l4, %l5 /* %l5 = (i/5120)*160 + (i%5120)/24; */ 153 154 call _rtld_bind /* Call _rtld_bind(obj, offset) */ 155 add %l5, %l6, %o1 /* %o1 = 32768 + ... */ 156 157 jmp %o0 /* return value == function address */ 158 restore /* Dump our stack frame */ 159 160 .section ".text" 161 .align 4 162 .global _rtld_bind_start_1 163 .type _rtld_bind_start_1,@function 164 _rtld_bind_start_1: # (y, x) 165 ldx [%o0 + (2*4)], %o0 /* Load object pointer from PLT2 */ 166 167 call _rtld_bind /* Call _rtld_bind(obj, offset) */ 168 srax %o1, 15, %o1 /* %o1 is the index to our PLT slot */ 169 170 jmp %o0 /* return value == function address */ 171 restore /* Dump our stack frame */ 172
Indexes created Thu Oct 02 01:09:59 GMT 2025