1 /* On-demand PLT fixup for shared objects.
2 Copyright (C) 1995-1999, 2000, 2001, 2002 Free Software Foundation, Inc.
3 This file is part of the GNU C Library.
5 The GNU C Library is free software; you can redistribute it and/or
6 modify it under the terms of the GNU Lesser General Public
7 License as published by the Free Software Foundation; either
8 version 2.1 of the License, or (at your option) any later version.
10 The GNU C Library 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 GNU
13 Lesser General Public License for more details.
15 You should have received a copy of the GNU Lesser General Public
16 License along with the GNU C Library; if not, write to the Free
17 Software Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA
24 #include "dynamic-link.h"
26 #if (!defined ELF_MACHINE_NO_RELA && !defined ELF_MACHINE_PLT_REL) \
28 # define PLTREL ElfW(Rela)
30 # define PLTREL ElfW(Rel)
34 # define VERSYMIDX(sym) (DT_NUM + DT_THISPROCNUM + DT_VERSIONTAGIDX (sym))
38 /* This function is called through a special trampoline from the PLT the
39 first time each PLT entry is called. We must perform the relocation
40 specified in the PLT of the given shared object, and return the resolved
41 function address to the trampoline, which will restart the original call
42 to that address. Future calls will bounce directly from the PLT to the
45 #ifndef ELF_MACHINE_NO_PLT
46 static ElfW(Addr
) __attribute_used__
48 # ifdef ELF_MACHINE_RUNTIME_FIXUP_ARGS
49 ELF_MACHINE_RUNTIME_FIXUP_ARGS
,
51 /* GKM FIXME: Fix trampoline to pass bounds so we can do
52 without the `__unbounded' qualifier. */
53 struct link_map
*__unbounded l
, ElfW(Word
) reloc_offset
)
55 const ElfW(Sym
) *const symtab
56 = (const void *) D_PTR (l
, l_info
[DT_SYMTAB
]);
57 const char *strtab
= (const void *) D_PTR (l
, l_info
[DT_STRTAB
]);
59 const PLTREL
*const reloc
60 = (const void *) (D_PTR (l
, l_info
[DT_JMPREL
]) + reloc_offset
);
61 const ElfW(Sym
) *sym
= &symtab
[ELFW(R_SYM
) (reloc
->r_info
)];
62 void *const rel_addr
= (void *)(l
->l_addr
+ reloc
->r_offset
);
66 /* The use of `alloca' here looks ridiculous but it helps. The goal is
67 to prevent the function from being inlined and thus optimized out.
68 There is no official way to do this so we use this trick. gcc never
69 inlines functions which use `alloca'. */
70 alloca (sizeof (int));
72 /* Sanity check that we're really looking at a PLT relocation. */
73 assert (ELFW(R_TYPE
)(reloc
->r_info
) == ELF_MACHINE_JMP_SLOT
);
75 /* Look up the target symbol. If the normal lookup rules are not
76 used don't look in the global scope. */
77 if (__builtin_expect (ELFW(ST_VISIBILITY
) (sym
->st_other
), 0) == 0)
79 switch (l
->l_info
[VERSYMIDX (DT_VERSYM
)] != NULL
)
83 const ElfW(Half
) *vernum
=
84 (const void *) D_PTR (l
, l_info
[VERSYMIDX (DT_VERSYM
)]);
85 ElfW(Half
) ndx
= vernum
[ELFW(R_SYM
) (reloc
->r_info
)];
86 const struct r_found_version
*version
= &l
->l_versions
[ndx
];
88 if (version
->hash
!= 0)
90 result
= INTUSE(_dl_lookup_versioned_symbol
) (strtab
100 result
= INTUSE(_dl_lookup_symbol
) (strtab
+ sym
->st_name
, l
, &sym
,
101 l
->l_scope
, ELF_RTYPE_CLASS_PLT
,
102 DL_LOOKUP_ADD_DEPENDENCY
);
105 /* Currently result contains the base load address (or link map)
106 of the object that defines sym. Now add in the symbol
108 value
= (sym
? LOOKUP_VALUE_ADDRESS (result
) + sym
->st_value
: 0);
112 /* We already found the symbol. The module (and therefore its load
113 address) is also known. */
114 value
= l
->l_addr
+ sym
->st_value
;
115 #ifdef DL_LOOKUP_RETURNS_MAP
120 /* And now perhaps the relocation addend. */
121 value
= elf_machine_plt_value (l
, reloc
, value
);
123 /* Finally, fix up the plt itself. */
124 if (__builtin_expect (GL(dl_bind_not
), 0))
127 return elf_machine_fixup_plt (l
, result
, reloc
, rel_addr
, value
);
131 #if !defined PROF && !defined ELF_MACHINE_NO_PLT && !__BOUNDED_POINTERS__
133 static ElfW(Addr
) __attribute_used__
135 #ifdef ELF_MACHINE_RUNTIME_FIXUP_ARGS
136 ELF_MACHINE_RUNTIME_FIXUP_ARGS
,
138 struct link_map
*l
, ElfW(Word
) reloc_offset
, ElfW(Addr
) retaddr
)
140 void (*mcount_fct
) (ElfW(Addr
), ElfW(Addr
)) = INTUSE(_dl_mcount
);
145 /* The use of `alloca' here looks ridiculous but it helps. The goal is
146 to prevent the function from being inlined, and thus optimized out.
147 There is no official way to do this so we use this trick. gcc never
148 inlines functions which use `alloca'. */
149 alloca (sizeof (int));
151 /* This is the address in the array where we store the result of previous
153 resultp
= &l
->l_reloc_result
[reloc_offset
/ sizeof (PLTREL
)];
158 /* This is the first time we have to relocate this object. */
159 const ElfW(Sym
) *const symtab
160 = (const void *) D_PTR (l
, l_info
[DT_SYMTAB
]);
161 const char *strtab
= (const void *) D_PTR (l
, l_info
[DT_STRTAB
]);
163 const PLTREL
*const reloc
164 = (const void *) (D_PTR (l
, l_info
[DT_JMPREL
]) + reloc_offset
);
165 const ElfW(Sym
) *sym
= &symtab
[ELFW(R_SYM
) (reloc
->r_info
)];
167 /* Sanity check that we're really looking at a PLT relocation. */
168 assert (ELFW(R_TYPE
)(reloc
->r_info
) == ELF_MACHINE_JMP_SLOT
);
170 /* Look up the target symbol. If the symbol is marked STV_PROTECTED
171 don't look in the global scope. */
172 if (__builtin_expect (ELFW(ST_VISIBILITY
) (sym
->st_other
), 0) == 0)
174 switch (l
->l_info
[VERSYMIDX (DT_VERSYM
)] != NULL
)
178 const ElfW(Half
) *vernum
=
179 (const void *) D_PTR (l
,l_info
[VERSYMIDX (DT_VERSYM
)]);
180 ElfW(Half
) ndx
= vernum
[ELFW(R_SYM
) (reloc
->r_info
)];
181 const struct r_found_version
*version
= &l
->l_versions
[ndx
];
183 if (version
->hash
!= 0)
185 result
= INTUSE(_dl_lookup_versioned_symbol
) (strtab
196 result
= INTUSE(_dl_lookup_symbol
) (strtab
+ sym
->st_name
, l
,
199 DL_LOOKUP_ADD_DEPENDENCY
);
202 /* Currently result contains the base load address (or link map)
203 of the object that defines sym. Now add in the symbol
205 value
= (sym
? LOOKUP_VALUE_ADDRESS (result
) + sym
->st_value
: 0);
209 /* We already found the symbol. The module (and therefore its load
210 address) is also known. */
211 value
= l
->l_addr
+ sym
->st_value
;
212 #ifdef DL_LOOKUP_RETURNS_MAP
216 /* And now perhaps the relocation addend. */
217 value
= elf_machine_plt_value (l
, reloc
, value
);
219 /* Store the result for later runs. */
220 if (__builtin_expect (! GL(dl_bind_not
), 1))
224 (*mcount_fct
) (retaddr
, value
);
229 #endif /* PROF && ELF_MACHINE_NO_PLT */
232 /* This macro is defined in dl-machine.h to define the entry point called
233 by the PLT. The `fixup' function above does the real work, but a little
234 more twiddling is needed to get the stack right and jump to the address
237 ELF_MACHINE_RUNTIME_TRAMPOLINE