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rmreloc.c revision 1.2 
      1 /* $NetBSD: rmreloc.c,v 1.2 2006/06/25 21:32:41 christos Exp $ */
      2 
      3 /*
      4  * Copyright 1996 John D. Polstra.
      5  * Copyright 1996 Matt Thomas <matt (at) 3am-software.com>
      6  * Copyright 2002 Charles M. Hannum <root (at) ihack.net>
      7  * All rights reserved.
      8  *
      9  * Redistribution and use in source and binary forms, with or without
     10  * modification, are permitted provided that the following conditions
     11  * are met:
     12  * 1. Redistributions of source code must retain the above copyright
     13  *    notice, this list of conditions and the following disclaimer.
     14  * 2. Redistributions in binary form must reproduce the above copyright
     15  *    notice, this list of conditions and the following disclaimer in the
     16  *    documentation and/or other materials provided with the distribution.
     17  * 3. All advertising materials mentioning features or use of this software
     18  *    must display the following acknowledgement:
     19  *      This product includes software developed by John Polstra.
     20  * 4. The name of the author may not be used to endorse or promote products
     21  *    derived from this software without specific prior written permission.
     22  *
     23  * THIS SOFTWARE IS PROVIDED BY THE AUTHOR ``AS IS'' AND ANY EXPRESS OR
     24  * IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES
     25  * OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED.
     26  * IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR ANY DIRECT, INDIRECT,
     27  * INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT
     28  * NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
     29  * DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
     30  * THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
     31  * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF
     32  * THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
     33  */
     34 /*
     35  * rmreloc.c - relocate an ELFish RISC OS relocatable module.
     36  */
     37 /*
     38  * This code is a heavily hacked version of parts of:
     39  * lib/libexec/ld.elf_so/headers.c
     40  * lib/libexec/ld.elf_so/arch/arm/mdreloc.c
     41  *
     42  * At present it only deals with DT_REL tables containing R_ARM_NONE
     43  * and R_ARM_RELATIVE relocations, because those are all that my
     44  * linker emits.  More can be added as needed.  Note that this has to
     45  * handle relocating already-relocated code, e.g. after *RMTidy, so
     46  * most relocations have to reference oldbase, which ld.elf_so just
     47  * assumes is zero.  There may be a cleverer way to do this.
     48  */
     49 
     50 #include <sys/types.h>
     51 #include <sys/stdint.h>
     52 #include <lib/libsa/stand.h>
     53 #define ELFSIZE 32
     54 #include <sys/exec_elf.h>
     55 
     56 #include <riscoscalls.h>
     57 
     58 os_error *relocate_self(Elf_Dyn *, caddr_t, caddr_t);
     59 
     60 #define assert(x) /* nothing */
     61 
     62 /*
     63  * While relocating ourselves, we must not refer to any global variables.
     64  * This includes _DYNAMIC -- the startup code finds it for us and passes
     65  * it to us along with the base address of the module.
     66  */
     67 
     68 typedef struct {
     69 	caddr_t         relocbase;	/* Reloc const = mapbase - *vaddrbase */
     70 	Elf_Dyn        *dynamic;	/* Dynamic section */
     71 	const Elf_Rel  *rel;		/* Relocation entries */
     72 	const Elf_Rel  *rellim;		/* Limit of Relocation entries */
     73 } Obj_Entry;
     74 
     75 #define rdbg(x) /* nothing */
     76 
     77 /*
     78  * It is possible for the compiler to emit relocations for unaligned data.
     79  * We handle this situation with these inlines.
     80  */
     81 #define	RELOC_ALIGNED_P(x) \
     82 	(((uintptr_t)(x) & (sizeof(void *) - 1)) == 0)
     83 
     84 static inline Elf_Addr
     85 load_ptr(void *where)
     86 {
     87 	Elf_Addr res;
     88 
     89 	memcpy(&res, where, sizeof(res));
     90 
     91 	return (res);
     92 }
     93 
     94 static inline void
     95 store_ptr(void *where, Elf_Addr val)
     96 {
     97 
     98 	memcpy(where, &val, sizeof(val));
     99 }
    100 
    101 static struct os_error bad_reloc = {
    102 	0, "Unhandled ELF redirection"
    103 };
    104 
    105 os_error *
    106 relocate_self(Elf_Dyn *dynamic, caddr_t oldbase, caddr_t newbase)
    107 {
    108 	Elf_Dyn *dynp;
    109 	Obj_Entry o = { 0 };
    110 	Obj_Entry *obj;
    111 	const Elf_Rel *rel;
    112 	Elf_Addr        relsz = 0;
    113 
    114 	obj = &o; obj->dynamic = dynamic; obj->relocbase = newbase;
    115 
    116 	for (dynp = obj->dynamic; dynp->d_tag != DT_NULL; ++dynp) {
    117 		switch (dynp->d_tag) {
    118 		case DT_REL:
    119 			obj->rel = (const Elf_Rel *)
    120 			    (obj->relocbase + dynp->d_un.d_ptr);
    121 			break;
    122 		case DT_RELSZ:
    123 			relsz = dynp->d_un.d_val;
    124 			break;
    125 		case DT_RELENT:
    126 			assert(dynp->d_un.d_val == sizeof(Elf_Rel));
    127 			break;
    128 		}
    129 	}
    130 
    131 	obj->rellim = (const Elf_Rel *)((caddr_t)obj->rel + relsz);
    132 
    133 	for (rel = obj->rel; rel < obj->rellim; rel++) {
    134 		Elf_Addr        *where;
    135 		Elf_Addr         tmp;
    136 
    137 		where = (Elf_Addr *)(obj->relocbase + rel->r_offset);
    138 
    139 		switch (ELF_R_TYPE(rel->r_info)) {
    140 		case R_TYPE(NONE):
    141 			break;
    142 
    143 		case R_TYPE(RELATIVE):	/* word32 B + A */
    144 			if (__predict_true(RELOC_ALIGNED_P(where))) {
    145 				tmp = *where + (Elf_Addr)obj->relocbase -
    146 				    (Elf_Addr)oldbase;
    147 				*where = tmp;
    148 			} else {
    149 				tmp = load_ptr(where) +
    150 				    (Elf_Addr)obj->relocbase -
    151 				    (Elf_Addr)oldbase;
    152 				store_ptr(where, tmp);
    153 			}
    154 			rdbg(("RELATIVE in %s --> %p", obj->path,
    155 			    (void *)tmp));
    156 			break;
    157 
    158 		default:
    159 			return &bad_reloc;
    160 		}
    161 	}
    162 	return NULL;
    163 }
    164