aboutsummaryrefslogtreecommitdiff
path: root/elf/dl-runtime.c
diff options
context:
space:
mode:
Diffstat (limited to 'elf/dl-runtime.c')
-rw-r--r--elf/dl-runtime.c100
1 files changed, 100 insertions, 0 deletions
diff --git a/elf/dl-runtime.c b/elf/dl-runtime.c
new file mode 100644
index 0000000..7e554bc
--- /dev/null
+++ b/elf/dl-runtime.c
@@ -0,0 +1,100 @@
+/* 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
+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"
+
+/* 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)
+{
+ 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 PLTREL *const reloc
+ = (const void *) (l->l_addr + 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_next = _dl_loaded;
+ if (l->l_prev)
+ l->l_prev->l_next = real_next;
+ scope = l;
+ }
+ 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_relplt (l, reloc, loadbase, definer);
+
+ return *(Elf32_Addr *) (l->l_addr + reloc->r_offset);
+}
+
+
+/* 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