-/* On-demand PLT fixup for shared objects. i386 version.
-Copyright (C) 1995 Free Software Foundation, Inc.
+/* On-demand PLT fixup for shared objects.
+Copyright (C) 1995, 1996 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
#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
- with 8(%esp) as the top of stack. */
-
-void
-_dl_runtime_resolve (Elf32_Word reloc_offset)
+/* Figure out the right type, Rel or Rela. */
+#define elf_machine_rel 1
+#define elf_machine_rela 2
+#if elf_machine_relplt == elf_machine_rel
+#define PLTREL Elf32_Rel
+#elif elf_machine_relplt == elf_machine_rela
+#define PLTREL Elf32_Rela
+#else
+#error "dl-machine.h bug: elf_machine_relplt not rel or rela"
+#endif
+#undef elf_machine_rel
+#undef elf_machine_rela
+
+/* We need to define the function as a local symbol so that the reference
+ in the trampoline code will be a local PC-relative call. Tell the
+ compiler not to worry that the function appears not to be called. */
+
+static Elf32_Addr fixup (struct link_map *l, Elf32_Word reloc_offset)
+ __attribute__ ((unused));
+
+/* 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. */
+
+static Elf32_Addr
+fixup (struct link_map *l, 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_addr + l->l_info[DT_SYMTAB]->d_un.d_ptr);
const char *strtab =
(const char *) (l->l_addr + l->l_info[DT_STRTAB]->d_un.d_ptr);
- const Elf32_Rel *const reloc
+ const PLTREL *const reloc
= (const void *) (l->l_addr + l->l_info[DT_JMPREL]->d_un.d_ptr +
reloc_offset);
}
else
scope = _dl_loaded;
-
+
definer = &symtab[ELF32_R_SYM (reloc->r_info)];
loadbase = _dl_lookup_symbol (strtab + definer->st_name, &definer,
scope, l->l_name, 0);
-
+
/* Restore list frobnication done above for DT_SYMBOLIC. */
l->l_next = real_next;
if (l->l_prev)
l->l_prev->l_next = l;
/* Apply the relocation with that value. */
- elf_machine_rel (l, reloc, loadbase, definer);
+ elf_machine_relplt (l, 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;
+ return *(Elf32_Addr *) (l->l_addr + reloc->r_offset);
+}
- /* 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 *) (l->l_addr + reloc->r_offset);
- return;
+/* 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. */
- return_insn: asm volatile ("ret");
-}
+ELF_MACHINE_RUNTIME_TRAMPOLINE
the offset on the stack, and then jump to the resolved address. */
got[2] = (Elf32_Addr) &_dl_runtime_resolve;
}
-}
+ /* This code is used in dl-runtime.c to call the `fixup' function
+ and then redirect to the address it returns. */
+#define ELF_MACHINE_RUNTIME_TRAMPOLINE asm ("\
+ .globl _dl_runtime_resolve
+ .type _dl_runtime_resolve, @function
+_dl_runtime_resolve:
+ call fixup # Args pushed by PLT.
+ addl $8, %esp # Pop args.
+ jmp *%eax # Jump to function address.
+");
+/* The PLT uses Elf32_Rel relocs. */
+#define elf_machine_relplt elf_machine_rel
+}
/* Mask identifying addresses reserved for the user program,
where the dynamic linker should not map anything. */
+++ /dev/null
-/* On-demand PLT fixup for shared objects. Stub 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. */
-
-#include <link.h>
-#include "dynamic-link.h"
-
-/* This function is not called in the normal way. The PLT jumps here, not
- using a call. */
-void
-_dl_runtime_resolve ()
-{
- struct link_map *l = ???;
- Elf32_Word reloc_offset = ???;
-
- 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);
-}
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