1 /* SPARC-specific values for a.out files 2 3 Copyright (C) 2001-2014 Free Software Foundation, Inc. 4 5 This program is free software; you can redistribute it and/or modify 6 it under the terms of the GNU General Public License as published by 7 the Free Software Foundation; either version 3 of the License, or 8 (at your option) any later version. 9 10 This program is distributed in the hope that it will be useful, 11 but WITHOUT ANY WARRANTY; without even the implied warranty of 12 MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the 13 GNU General Public License for more details. 14 15 You should have received a copy of the GNU General Public License 16 along with this program; if not, write to the Free Software 17 Foundation, Inc., 51 Franklin Street - Fifth Floor, Boston, 18 MA 02110-1301, USA. */ 19 20 /* Some systems, e.g., AIX, may have defined this in header files already 21 included. */ 22 #undef TARGET_PAGE_SIZE 23 #define TARGET_PAGE_SIZE 0x2000 /* 8K. aka NBPG in <sys/param.h> */ 24 /* Note that some SPARCs have 4K pages, some 8K, some others. */ 25 26 #define SEG_SIZE_SPARC TARGET_PAGE_SIZE 27 #define SEG_SIZE_SUN3 0x20000 /* Resolution of r/w protection hw */ 28 29 #define TEXT_START_ADDR TARGET_PAGE_SIZE /* Location 0 is not accessible */ 30 #define N_HEADER_IN_TEXT(x) 1 31 32 /* Non-default definitions of the accessor macros... */ 33 34 /* Segment size varies on Sun-3 versus Sun-4. */ 35 36 #define N_SEGSIZE(x) (N_MACHTYPE(x) == M_SPARC? SEG_SIZE_SPARC: \ 37 N_MACHTYPE(x) == M_68020? SEG_SIZE_SUN3: \ 38 /* Guess? */ TARGET_PAGE_SIZE) 39 40 /* Virtual Address of text segment from the a.out file. For OMAGIC, 41 (almost always "unlinked .o's" these days), should be zero. 42 Sun added a kludge so that shared libraries linked ZMAGIC get 43 an address of zero if a_entry (!!!) is lower than the otherwise 44 expected text address. These kludges have gotta go! 45 For linked files, should reflect reality if we know it. */ 46 47 #define N_SHARED_LIB(x) ((x).a_entry < TEXT_START_ADDR \ 48 && (x).a_text >= EXEC_BYTES_SIZE) 49 50 /* This differs from the version in aout64.h (which we override by defining 51 it here) only for NMAGIC (we return TEXT_START_ADDR+EXEC_BYTES_SIZE; 52 they return 0). */ 53 54 #define N_TXTADDR(x) \ 55 (N_MAGIC(x)==OMAGIC? 0 \ 56 : (N_MAGIC(x) == ZMAGIC && (x).a_entry < TEXT_START_ADDR)? 0 \ 57 : TEXT_START_ADDR+EXEC_BYTES_SIZE) 58 59 /* When a file is linked against a shared library on SunOS 4, the 60 dynamic bit in the exec header is set, and the first symbol in the 61 symbol table is __DYNAMIC. Its value is the address of the 62 following structure. */ 63 64 struct external_sun4_dynamic 65 { 66 /* The version number of the structure. SunOS 4.1.x creates files 67 with version number 3, which is what this structure is based on. 68 According to gdb, version 2 is similar. I believe that version 2 69 used a different type of procedure linkage table, and there may 70 have been other differences. */ 71 bfd_byte ld_version[4]; 72 /* The virtual address of a 28 byte structure used in debugging. 73 The contents are filled in at run time by ld.so. */ 74 bfd_byte ldd[4]; 75 /* The virtual address of another structure with information about 76 how to relocate the executable at run time. */ 77 bfd_byte ld[4]; 78 }; 79 80 /* The size of the debugging structure pointed to by the debugger 81 field of __DYNAMIC. */ 82 #define EXTERNAL_SUN4_DYNAMIC_DEBUGGER_SIZE (24) 83 84 /* The structure pointed to by the linker field of __DYNAMIC. As far 85 as I can tell, most of the addresses in this structure are offsets 86 within the file, but some are actually virtual addresses. */ 87 88 struct internal_sun4_dynamic_link 89 { 90 /* Linked list of loaded objects. This is filled in at runtime by 91 ld.so and probably by dlopen. */ 92 unsigned long ld_loaded; 93 94 /* The address of the list of names of shared objects which must be 95 included at runtime. Each entry in the list is 16 bytes: the 4 96 byte address of the string naming the object (e.g., for -lc this 97 is "c"); 4 bytes of flags--the high bit is whether to search for 98 the object using the library path; the 2 byte major version 99 number; the 2 byte minor version number; the 4 byte address of 100 the next entry in the list (zero if this is the last entry). The 101 version numbers seem to only be non-zero when doing library 102 searching. */ 103 unsigned long ld_need; 104 105 /* The address of the path to search for the shared objects which 106 must be included. This points to a string in PATH format which 107 is generated from the -L arguments to the linker. According to 108 the man page, ld.so implicitly adds ${LD_LIBRARY_PATH} to the 109 beginning of this string and /lib:/usr/lib:/usr/local/lib to the 110 end. The string is terminated by a null byte. This field is 111 zero if there is no additional path. */ 112 unsigned long ld_rules; 113 114 /* The address of the global offset table. This appears to be a 115 virtual address, not a file offset. The first entry in the 116 global offset table seems to be the virtual address of the 117 sun4_dynamic structure (the same value as the __DYNAMIC symbol). 118 The global offset table is used for PIC code to hold the 119 addresses of variables. A dynamically linked file which does not 120 itself contain PIC code has a four byte global offset table. */ 121 unsigned long ld_got; 122 123 /* The address of the procedure linkage table. This appears to be a 124 virtual address, not a file offset. 125 126 On a SPARC, the table is composed of 12 byte entries, each of 127 which consists of three instructions. The first entry is 128 sethi %hi(0),%g1 129 jmp %g1 130 nop 131 These instructions are changed by ld.so into a jump directly into 132 ld.so itself. Each subsequent entry is 133 save %sp, -96, %sp 134 call <address of first entry in procedure linkage table> 135 <reloc_number | 0x01000000> 136 The reloc_number is the number of the reloc to use to resolve 137 this entry. The reloc will be a JMP_SLOT reloc against some 138 symbol that is not defined in this object file but should be 139 defined in a shared object (if it is not, ld.so will report a 140 runtime error and exit). The constant 0x010000000 turns the 141 reloc number into a sethi of %g0, which does nothing since %g0 is 142 hardwired to zero. 143 144 When one of these entries is executed, it winds up calling into 145 ld.so. ld.so looks at the reloc number, available via the return 146 address, to determine which entry this is. It then looks at the 147 reloc and patches up the entry in the table into a sethi and jmp 148 to the real address followed by a nop. This means that the reloc 149 lookup only has to happen once, and it also means that the 150 relocation only needs to be done if the function is actually 151 called. The relocation is expensive because ld.so must look up 152 the symbol by name. 153 154 The size of the procedure linkage table is given by the ld_plt_sz 155 field. */ 156 unsigned long ld_plt; 157 158 /* The address of the relocs. These are in the same format as 159 ordinary relocs. Symbol index numbers refer to the symbols 160 pointed to by ld_stab. I think the only way to determine the 161 number of relocs is to assume that all the bytes from ld_rel to 162 ld_hash contain reloc entries. */ 163 unsigned long ld_rel; 164 165 /* The address of a hash table of symbols. The hash table has 166 roughly the same number of entries as there are dynamic symbols; 167 I think the only way to get the exact size is to assume that 168 every byte from ld_hash to ld_stab is devoted to the hash table. 169 170 Each entry in the hash table is eight bytes. The first four 171 bytes are a symbol index into the dynamic symbols. The second 172 four bytes are the index of the next hash table entry in the 173 bucket. The ld_buckets field gives the number of buckets, say B. 174 The first B entries in the hash table each start a bucket which 175 is chained through the second four bytes of each entry. A value 176 of zero ends the chain. 177 178 The hash function is simply 179 h = 0; 180 while (*string != '\0') 181 h = (h << 1) + *string++; 182 h &= 0x7fffffff; 183 184 To look up a symbol, compute the hash value of the name. Take 185 the modulos of hash value and the number of buckets. Start at 186 that entry in the hash table. See if the symbol (from the first 187 four bytes of the hash table entry) has the name you are looking 188 for. If not, use the chain field (the second four bytes of the 189 hash table entry) to move on to the next entry in this bucket. 190 If the chain field is zero you have reached the end of the 191 bucket, and the symbol is not in the hash table. */ 192 unsigned long ld_hash; 193 194 /* The address of the symbol table. This is a list of 195 external_nlist structures. The string indices are relative to 196 the ld_symbols field. I think the only way to determine the 197 number of symbols is to assume that all the bytes between ld_stab 198 and ld_symbols are external_nlist structures. */ 199 unsigned long ld_stab; 200 201 /* I don't know what this is for. It seems to always be zero. */ 202 unsigned long ld_stab_hash; 203 204 /* The number of buckets in the hash table. */ 205 unsigned long ld_buckets; 206 207 /* The address of the symbol string table. The first string in this 208 string table need not be the empty string. */ 209 unsigned long ld_symbols; 210 211 /* The size in bytes of the symbol string table. */ 212 unsigned long ld_symb_size; 213 214 /* The size in bytes of the text segment. */ 215 unsigned long ld_text; 216 217 /* The size in bytes of the procedure linkage table. */ 218 unsigned long ld_plt_sz; 219 }; 220 221 /* The external form of the structure. */ 222 223 struct external_sun4_dynamic_link 224 { 225 bfd_byte ld_loaded[4]; 226 bfd_byte ld_need[4]; 227 bfd_byte ld_rules[4]; 228 bfd_byte ld_got[4]; 229 bfd_byte ld_plt[4]; 230 bfd_byte ld_rel[4]; 231 bfd_byte ld_hash[4]; 232 bfd_byte ld_stab[4]; 233 bfd_byte ld_stab_hash[4]; 234 bfd_byte ld_buckets[4]; 235 bfd_byte ld_symbols[4]; 236 bfd_byte ld_symb_size[4]; 237 bfd_byte ld_text[4]; 238 bfd_byte ld_plt_sz[4]; 239 }; 240
