/* On-demand PLT fixup for shared objects. Copyright (C) 1995-1999, 2000 Free Software Foundation, Inc. This file is part of the GNU C Library. The GNU C Library is free software; you can redistribute it and/or modify it under the terms of the GNU Library General Public License as published by the Free Software Foundation; either version 2 of the License, or (at your option) any later version. The GNU C Library is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU Library General Public License for more details. You should have received a copy of the GNU Library General Public License along with the GNU C Library; see the file COPYING.LIB. If not, write to the Free Software Foundation, Inc., 59 Temple Place - Suite 330, Boston, MA 02111-1307, USA. */ #include <alloca.h> #include <stdlib.h> #include <unistd.h> #include <ldsodefs.h> #include "dynamic-link.h" #if !defined ELF_MACHINE_NO_RELA || ELF_MACHINE_NO_REL # define PLTREL ElfW(Rela) #else # define PLTREL ElfW(Rel) #endif #ifndef VERSYMIDX # define VERSYMIDX(sym) (DT_NUM + DT_THISPROCNUM + DT_VERSIONTAGIDX (sym)) #endif /* This function is called through a special trampoline from the PLT the first time each PLT entry is called. We must perform the relocation specified in the PLT of the given shared object, and return the resolved function address to the trampoline, which will restart the original call to that address. Future calls will bounce directly from the PLT to the function. */ #ifndef ELF_MACHINE_NO_PLT static ElfW(Addr) __attribute__ ((unused)) fixup ( # ifdef ELF_MACHINE_RUNTIME_FIXUP_ARGS ELF_MACHINE_RUNTIME_FIXUP_ARGS, # endif struct link_map *l, ElfW(Word) reloc_offset) { const ElfW(Sym) *const symtab = (const void *) D_PTR (l, l_info[DT_SYMTAB]); const char *strtab = (const void *) D_PTR (l, l_info[DT_STRTAB]); const PLTREL *const reloc = (const void *) (D_PTR (l, l_info[DT_JMPREL]) + reloc_offset); const ElfW(Sym) *sym = &symtab[ELFW(R_SYM) (reloc->r_info)]; void *const rel_addr = (void *)(l->l_addr + reloc->r_offset); lookup_t result; ElfW(Addr) value; /* The use of `alloca' here looks ridiculous but it helps. The goal is to prevent the function from being inlined and thus optimized out. There is no official way to do this so we use this trick. gcc never inlines functions which use `alloca'. */ alloca (sizeof (int)); /* Sanity check that we're really looking at a PLT relocation. */ assert (ELFW(R_TYPE)(reloc->r_info) == ELF_MACHINE_JMP_SLOT); /* Look up the target symbol. If the normal lookup rules are not used don't look in the global scope. */ if (__builtin_expect (ELFW(ST_VISIBILITY) (sym->st_other), 0) == 0) { switch (l->l_info[VERSYMIDX (DT_VERSYM)] != NULL) { default: { const ElfW(Half) *vernum = (const void *) D_PTR (l, l_info[VERSYMIDX (DT_VERSYM)]); ElfW(Half) ndx = vernum[ELFW(R_SYM) (reloc->r_info)]; const struct r_found_version *version = &l->l_versions[ndx]; if (version->hash != 0) { result = _dl_lookup_versioned_symbol (strtab + sym->st_name, l, &sym, l->l_scope, version, ELF_MACHINE_JMP_SLOT); break; } } case 0: result = _dl_lookup_symbol (strtab + sym->st_name, l, &sym, l->l_scope, ELF_MACHINE_JMP_SLOT); } /* Currently result contains the base load address (or link map) of the object that defines sym. Now add in the symbol offset. */ value = (sym ? LOOKUP_VALUE_ADDRESS (result) + sym->st_value : 0); } else { /* We already found the symbol. The module (and therefore its load address) is also known. */ value = l->l_addr + sym->st_value; #ifdef DL_LOOKUP_RETURNS_MAP result = l; #endif } /* And now perhaps the relocation addend. */ value = elf_machine_plt_value (l, reloc, value); /* Finally, fix up the plt itself. */ return elf_machine_fixup_plt (l, result, reloc, rel_addr, value); } #endif #if !defined PROF && !defined ELF_MACHINE_NO_PLT static ElfW(Addr) __attribute__ ((unused)) profile_fixup ( #ifdef ELF_MACHINE_RUNTIME_FIXUP_ARGS ELF_MACHINE_RUNTIME_FIXUP_ARGS, #endif struct link_map *l, ElfW(Word) reloc_offset, ElfW(Addr) retaddr) { void (*mcount_fct) (ElfW(Addr), ElfW(Addr)) = _dl_mcount; ElfW(Addr) *resultp; lookup_t result; ElfW(Addr) value; /* The use of `alloca' here looks ridiculous but it helps. The goal is to prevent the function from being inlined, and thus optimized out. There is no official way to do this so we use this trick. gcc never inlines functions which use `alloca'. */ alloca (sizeof (int)); /* This is the address in the array where we store the result of previous relocations. */ resultp = &l->l_reloc_result[reloc_offset / sizeof (PLTREL)]; value = *resultp; if (value == 0) { /* This is the first time we have to relocate this object. */ const ElfW(Sym) *const symtab = (const void *) D_PTR (l, l_info[DT_SYMTAB]); const char *strtab = (const void *) D_PTR (l, l_info[DT_STRTAB]); const PLTREL *const reloc = (const void *) (D_PTR (l, l_info[DT_JMPREL]) + reloc_offset); const ElfW(Sym) *sym = &symtab[ELFW(R_SYM) (reloc->r_info)]; /* Sanity check that we're really looking at a PLT relocation. */ assert (ELFW(R_TYPE)(reloc->r_info) == ELF_MACHINE_JMP_SLOT); /* Look up the target symbol. If the symbol is marked STV_PROTECTED don't look in the global scope. */ if (__builtin_expect (ELFW(ST_VISIBILITY) (sym->st_other), 0) == 0) { switch (l->l_info[VERSYMIDX (DT_VERSYM)] != NULL) { default: { const ElfW(Half) *vernum = (const void *) D_PTR (l,l_info[VERSYMIDX (DT_VERSYM)]); ElfW(Half) ndx = vernum[ELFW(R_SYM) (reloc->r_info)]; const struct r_found_version *version = &l->l_versions[ndx]; if (version->hash != 0) { result = _dl_lookup_versioned_symbol(strtab + sym->st_name, l, &sym, l->l_scope, version, ELF_MACHINE_JMP_SLOT); break; } } case 0: result = _dl_lookup_symbol (strtab + sym->st_name, l, &sym, l->l_scope, ELF_MACHINE_JMP_SLOT); } /* Currently result contains the base load address (or link map) of the object that defines sym. Now add in the symbol offset. */ value = (sym ? LOOKUP_VALUE_ADDRESS (result) + sym->st_value : 0); } else { /* We already found the symbol. The module (and therefore its load address) is also known. */ value = l->l_addr + sym->st_value; #ifdef DL_LOOKUP_RETURNS_MAP result = l; #endif } /* And now perhaps the relocation addend. */ value = elf_machine_plt_value (l, reloc, value); /* Store the result for later runs. */ *resultp = value; } (*mcount_fct) (retaddr, value); return value; } #endif /* PROF && ELF_MACHINE_NO_PLT */ /* This macro is defined in dl-machine.h to define the entry point called by the PLT. The `fixup' function above does the real work, but a little more twiddling is needed to get the stack right and jump to the address finally resolved. */ ELF_MACHINE_RUNTIME_TRAMPOLINE