diff options
Diffstat (limited to 'sysdeps/i386')
| -rw-r--r-- | sysdeps/i386/dl-machine.h | 169 | ||||
| -rw-r--r-- | sysdeps/i386/dl-runtime.c | 92 | ||||
| -rw-r--r-- | sysdeps/i386/elf/start.S | 86 |
3 files changed, 347 insertions, 0 deletions
diff --git a/sysdeps/i386/dl-machine.h b/sysdeps/i386/dl-machine.h new file mode 100644 index 0000000000..5e1ee2a413 --- /dev/null +++ b/sysdeps/i386/dl-machine.h @@ -0,0 +1,169 @@ +/* Machine-dependent ELF dynamic relocation inline functions. i386 version. +Copyright (C) 1995 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., 675 Mass Ave, +Cambridge, MA 02139, USA. */ + +#define ELF_MACHINE_NAME "i386" + +#include <assert.h> +#include <string.h> +#include <link.h> + + +/* Return nonzero iff E_MACHINE is compatible with the running host. */ +static inline int +elf_machine_matches_host (Elf32_Half e_machine) +{ + switch (e_machine) + { + case EM_386: + case EM_486: + return 1; + default: + return 0; + } +} + + +/* Return the run-time address of the _GLOBAL_OFFSET_TABLE_. + Must be inlined in a function which uses global data. */ +static inline Elf32_Addr * +elf_machine_got (void) +{ + register Elf32_Addr *got asm ("%ebx"); + return got; +} + + +/* Return the run-time load address of the shared object. */ +static inline Elf32_Addr +elf_machine_load_address (void) +{ + Elf32_Addr addr; + asm (" call here\n" + "here: popl %0\n" + " subl $here, %0" + : "=r" (addr)); + return addr; +} +/* The `subl' insn above will contain an R_386_32 relocation entry + intended to insert the run-time address of the label `here'. + This will be the first relocation in the text of the dynamic linker; + we skip it to avoid trying to modify read-only text in this early stage. */ +#define ELF_MACHINE_BEFORE_RTLD_RELOC(dynamic_info) \ + ++(const Elf32_Rel *) (dynamic_info)[DT_REL]->d_un.d_ptr; + +/* Perform the relocation specified by RELOC and SYM (which is fully resolved). + LOADADDR is the load address of the object; INFO is an array indexed + by DT_* of the .dynamic section info. */ + +static inline void +elf_machine_rel (Elf32_Addr loadaddr, Elf32_Dyn *info[DT_NUM], + const Elf32_Rel *reloc, + Elf32_Addr sym_loadaddr, const Elf32_Sym *sym) +{ + Elf32_Addr *const reloc_addr = (Elf32_Addr *) reloc->r_offset; + const Elf32_Addr sym_value = sym_loadaddr + sym->st_value; + + switch (ELF32_R_TYPE (reloc->r_info)) + { + case R_386_COPY: + memcpy (reloc_addr, (void *) sym_value, sym->st_size); + break; + case R_386_GLOB_DAT: + case R_386_JMP_SLOT: + *reloc_addr = sym_value; + break; + case R_386_32: + *reloc_addr += sym_value; + break; + case R_386_RELATIVE: + *reloc_addr += loadaddr; + break; + case R_386_PC32: + *reloc_addr = sym_value - (Elf32_Addr) reloc_addr; + break; + default: + assert (! "unexpected dynamic reloc type"); + break; + } +} + + +/* The i386 never uses Elf32_Rela relocations. */ +static inline void +elf_machine_rela (Elf32_Addr loadaddr, Elf32_Dyn *info[DT_NUM], + const Elf32_Rela *reloc, + Elf32_Addr sym_loadaddr, const Elf32_Sym *sym) +{ + _dl_signal_error (0, "Elf32_Rela relocation requested -- unused on i386"); +} + + +/* Set up the loaded object described by L so its unrelocated PLT + entries will jump to the on-demand fixup code in dl-runtime.c. */ + +static inline void +elf_machine_runtime_setup (struct link_map *l) +{ + extern void _dl_runtime_resolve (Elf32_Word); + /* The GOT entries for functions in the PLT have not yet been filled + in. Their initial contents will arrange when called to push an + offset into the .rel.plt section, push _GLOBAL_OFFSET_TABLE_[1], + and then jump to _GLOBAL_OFFSET_TABLE[2]. */ + Elf32_Addr *got = (Elf32_Addr *) l->l_info[DT_PLTGOT]->d_un.d_ptr; + got[1] = (Elf32_Addr) l; /* Identify this shared object. */ + /* This function will get called to fix up the GOT entry indicated by + the offset on the stack, and then jump to the resolved address. */ + got[2] = (Elf32_Addr) &_dl_runtime_resolve; +} + + +/* Initial entry point code for the dynamic linker. + The C function `_dl_start' is the real entry point; + its return value is the user program's entry point. */ + +#define RTLD_START asm ("\ +.text\n\ +.globl _start\n\ +_start: call _dl_start\n\ + # Save the user entry point address in %ebx.\n\ + movl %eax, %ebx\n\ + # Call _dl_init_next to return the address of an initializer\n\ + # function to run.\n\ +0: call _dl_init_next@PLT\n\ + # Check for zero return, when out of initializers.\n\ + testl %eax,%eax\n\ + jz 1f\n\ + # Call the shared object initializer function.\n\ + # NOTE: We depend only on the registers (%ebx)\n\ + # and the return address pushed by this call;\n\ + # the initializer is called with the stack just\n\ + # as it appears on entry, and it is free to move\n\ + # the stack around, as long as it winds up jumping to\n\ + # the return address on the top of the stack.\n\ + call *%eax\n\ + # Loop to call _dl_init_next for the next initializer.\n\ + jmp 0b\n\ + # Pass our finalizer function to the user in %edx, as per ELF ABI.\n\ +1: call 2f\n\ +2: popl %eax\n\ + addl $_GLOBAL_OFFSET_TABLE_+[.-2b], %eax\n\ + leal _dl_fini@GOT(%eax), %edx\n\ + # Jump to the user entry point.\n\ + jmp *%ebx\n\ +"); diff --git a/sysdeps/i386/dl-runtime.c b/sysdeps/i386/dl-runtime.c new file mode 100644 index 0000000000..897524fdd3 --- /dev/null +++ b/sysdeps/i386/dl-runtime.c @@ -0,0 +1,92 @@ +/* On-demand PLT fixup for shared objects. i386 version. +Copyright (C) 1995 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., 675 Mass Ave, +Cambridge, MA 02139, USA. */ + +register void *sp asm ("%esp"); + +#include <link.h> +#include "dynamic-link.h" + +/* This function is not called in the normal way. The PLT jumps here, not + using a call. The stack looks like this: + +-->8(%esp) address to return to the caller of the function in the PLT + 4(%esp) relocation offset for this PLT entry + 0(%esp) identifier for this shared object (struct link_map *) + + The user expects the real function the PLT refers to to be entered + 8(%esp) as the top of stack. */ + +void +_dl_runtime_resolve (Elf32_Word reloc_offset) +{ + __label__ return_insn; + struct link_map *l = (void *) &(&reloc_offset)[-1]; + + const Elf32_Sym *const symtab + = (const Elf32_Sym *) l->l_info[DT_SYMTAB]->d_un.d_ptr; + const char *strtab + = ((void *) l->l_addr + l->l_info[DT_STRTAB]->d_un.d_ptr); + + const Elf32_Rel *const reloc = (void *) (l->l_info[DT_JMPREL]->d_un.d_ptr + + reloc_offset); + + const Elf32_Sym *definer; + Elf32_Addr loadbase; + struct link_map *scope, *real_next; + + /* Look up the symbol's run-time value. */ + + real_next = l->l_next; + if (l->l_info[DT_SYMBOLIC]) + { + l->l_prev->l_next = real_next; + l->l_next = _dl_loaded; + scope = l; + } + else + scope = _dl_loaded; + + definer = &symtab[ELF32_R_SYM (reloc->r_info)]; + loadbase = _dl_lookup_symbol (strtab + definer->st_name, &definer, scope); + + /* Restore list frobnication done above for DT_SYMBOLIC. */ + l->l_next = real_next; + l->l_prev->l_next = l; + + /* Apply the relocation with that value. */ + elf_machine_rel (l->l_addr, l->l_info, reloc, loadbase, definer); + + /* The top of the stack is the word we set L from; but this location + holds the address we will return to. Store there the address of a + "ret" instruction, which will pop the stack and run the code at the + address in the next stack word. */ + (&reloc_offset)[-1] = (Elf32_Word) &&return_insn; + + /* The next stack word is our argument RELOC_OFFSET; but that "ret" will + pop and jump to this location, and the next stack word is the user's + return address. So store here the resolved address of the function + referred to by this PLT entry; once "ret" pops this address, the + function in the shared object will run with the stack arranged just as + when the user entered the PLT. */ + (&reloc_offset)[0] = *(Elf32_Word *) reloc->r_offset; + + return; + + return_insn: asm volatile ("ret"); +} diff --git a/sysdeps/i386/elf/start.S b/sysdeps/i386/elf/start.S new file mode 100644 index 0000000000..5c29ce412a --- /dev/null +++ b/sysdeps/i386/elf/start.S @@ -0,0 +1,86 @@ +/* Startup code compliant to the ELF i386 ABI. +Copyright (C) 1995 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., 675 Mass Ave, +Cambridge, MA 02139, USA. */ + +/* This is the canonical entry point, usually the first thing in the text + segment. The SVR4/i386 ABI (pages 3-31, 3-32) says that when the entry + point runs, most registers' values are unspecified, except for: + + %edx Contains a function pointer to be registered with `atexit'. + This is how the dynamic linker arranges to have DT_FINI + functions called for shared libraries that have been loaded + before this code runs. + + %esp The stack contains the arguments and environment: + 0(%esp) argc + 4(%esp) argv[0] + ... + (4*argc)(%esp) NULL + (4*(argc+1))(%esp) envp[0] + ... + NULL +*/ + + .text + .globl _start +_start: + /* Clear the frame pointer. The ABI suggests this be done, to mark + the outermost frame obviously. */ + movl $0, %ebp + + /* %edx contains the address of the shared library termination + function, which we will register with `atexit' to be called by + `exit'. I suspect that on some systems, and when statically + linked, this will not be set by anything to any function + pointer; hopefully it will be zero so we don't try to call + random pointers. */ + testl %edx + jeq nofini + pushl %edx + call atexit + addl $4, %esp +nofini: + + /* Do essential libc initialization. In statically linked + programs under the GNU Hurd, this is what sets up the + arguments on the stack for the code below. */ + call __libc_init_first + + /* Extract the arguments and environment as encoded on the stack + and set up the arguments for `main': argc, argv, envp. */ + popl %esi /* Pop the argument count. */ + leal 4(%esp,%esi,4), %eax /* envp = &argv[argc + 1] */ + movl %eax, _environ /* Store it in the global variable. */ + pushl %eax /* Push third argument: envp. */ + leal 4(%esp), %eax /* argv starts just above that word. */ + pushl %eax /* Push second argument: argv. */ + pushl %esi /* Push first argument: argc. */ + + /* Call `_init', which is the entry point to our own `.init' + section; and register with `atexit' to have `exit' call + `_fini', which is the entry point to our own `.fini' section. */ + call _init + pushl $_fini + call atexit + addl $4, %esp + + /* Call the user's main function, and exit with its value. */ + call main + pushl %eax + call exit /* This should never return. */ + hlt /* Crash if somehow it does return. */ |