1 /* Machine-dependent ELF dynamic relocation inline functions. Alpha version.
2 Copyright (C) 1996 Free Software Foundation, Inc.
3 This file is part of the GNU C Library.
4 Contributed by Richard Henderson <rth@tamu.edu>.
6 The GNU C Library is free software; you can redistribute it and/or
7 modify it under the terms of the GNU Library General Public License as
8 published by the Free Software Foundation; either version 2 of the
9 License, or (at your option) any later version.
11 The GNU C Library is distributed in the hope that it will be useful,
12 but WITHOUT ANY WARRANTY; without even the implied warranty of
13 MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
14 Library General Public License for more details.
16 You should have received a copy of the GNU Library General Public
17 License along with the GNU C Library; see the file COPYING.LIB. If
18 not, write to the Free Software Foundation, Inc., 675 Mass Ave,
19 Cambridge, MA 02139, USA. */
21 /* This was written in the absence of an ABI -- don't expect
22 it to remain unchanged. */
25 #define dl_machine_h 1
27 #define ELF_MACHINE_NAME "alpha"
33 /* Return nonzero iff E_MACHINE is compatible with the running host. */
35 elf_machine_matches_host (Elf64_Word e_machine)
37 return e_machine == EM_ALPHA;
40 /* Return the run-time address of the _GLOBAL_OFFSET_TABLE_.
41 Must be inlined in a function which uses global data. */
42 static inline Elf64_Addr *
43 elf_machine_got (void)
45 register Elf64_Addr gp __asm__("$29");
46 return (Elf64_Addr *)(gp - 0x8000);
49 /* Return the run-time load address of the shared object. */
50 static inline Elf64_Addr
51 elf_machine_load_address (void)
53 /* NOTE: While it is generally unfriendly to put data in the text
54 segment, it is only slightly less so when the "data" is an
55 instruction. While we don't have to worry about GLD just yet, an
56 optimizing linker might decide that our "data" is an unreachable
57 instruction and throw it away -- with the right switches, DEC's
58 linker will do this. What ought to happen is we should add
59 something to GAS to allow us access to the new GPREL_HI32/LO32
60 relocation types stolen from OSF/1 3.0. */
61 /* This code relies on the fact that BRADDR relocations do not
62 appear in dynamic relocation tables. Not that that would be very
63 useful anyway -- br/bsr has a 4MB range and the shared libraries
64 are usually many many terabytes away. */
70 ".weak __load_address_undefined\n\t"
71 "br $0, __load_address_undefined\n"
75 zero_disp = *(int *)dot;
76 zero_disp = (zero_disp << 43) >> 41;
78 return dot + 4 + zero_disp;
81 /* Set up the loaded object described by L so its unrelocated PLT
82 entries will jump to the on-demand fixup code in dl-runtime.c. */
85 elf_machine_runtime_setup (struct link_map *l, int lazy)
88 extern void _dl_runtime_resolve (void);
90 if (l->l_info[DT_JMPREL] && lazy)
92 /* The GOT entries for the functions in the PLT have not been
93 filled in yet. Their initial contents are directed to the
94 PLT which arranges for the dynamic linker to be called. */
95 plt = l->l_addr + l->l_info[DT_PLTGOT]->d_un.d_ptr;
97 /* This function will be called to perform the relocation. */
98 *(Elf64_Addr *)(plt + 16) = (Elf64_Addr) &_dl_runtime_resolve;
100 /* Identify this shared object */
101 *(Elf64_Addr *)(plt + 24) = (Elf64_Addr) l;
105 /* This code is used in dl-runtime.c to call the `fixup' function
106 and then redirect to the address it returns. */
107 #define ELF_MACHINE_RUNTIME_TRAMPOLINE asm ( \
108 "/* Trampoline for _dl_runtime_resolver */
109 .globl _dl_runtime_resolve
110 .ent _dl_runtime_resolve
114 /* Preserve all registers that C normally doesn't. */
136 .mask 0x27ff01ff, -168
141 /* Set up the arguments for _dl_runtime_resolve. */
142 /* $16 = link_map out of plt0 */
144 /* $17 = offset of reloc entry */
148 /* Move the destination address to a safe place. */
150 /* Restore program registers. */
172 /* Clean up and turn control to the destination */
175 .end _dl_runtime_resolve");
177 /* The PLT uses Elf_Rel relocs. */
178 #define elf_machine_relplt elf_machine_rela
180 /* Mask identifying addresses reserved for the user program,
181 where the dynamic linker should not map anything. */
183 #define ELF_MACHINE_USER_ADDRESS_MASK (~0x1FFFFFFFFUL)
185 /* Initial entry point code for the dynamic linker.
186 The C function `_dl_start' is the real entry point;
187 its return value is the user program's entry point. */
189 #define RTLD_START asm ("\
192 .globl _dl_start_user
196 /* Pass pointer to argument block to _dl_start. */
198 bsr $26, _dl_start..ng
200 /* Save the user entry point address in s0. */
202 /* See if we were run as a command with the executable file
203 name as an extra leading argument. If so, adjust the stack
204 pointer to skip _dl_skip_args words. */
205 ldl $1, _dl_skip_args
211 /* Load _dl_default_scope[2] into s1 to pass to _dl_init_next. */
212 0: ldq $10, _dl_default_scope+16
213 /* Call _dl_init_next to return the address of an initalizer
216 jsr $26, _dl_init_next
223 2: /* Pass our finalizer function to the user in $0. */
225 /* Jump to the user's entry point. */
229 /* Nonzero iff TYPE describes relocation of a PLT entry, so
230 PLT entries should not be allowed to define the value. */
231 #define elf_machine_pltrel_p(type) ((type) == R_ALPHA_JMP_SLOT)
233 /* The alpha never uses Elf64_Rel relocations. */
234 #define ELF_MACHINE_NO_REL 1
236 #endif /* !dl_machine_h */
240 /* Fix up the instructions of a PLT entry to invoke the function
241 rather than the dynamic linker. */
243 elf_alpha_fix_plt(struct link_map *l,
244 const Elf64_Rela *reloc,
248 const Elf64_Rela *rela_plt;
252 /* Recover the PLT entry address by calculating reloc's index into the
253 .rela.plt, and finding that entry in the .plt. */
255 rela_plt = (void *)(l->l_addr + l->l_info[DT_JMPREL]->d_un.d_ptr);
257 plte = (void *)(l->l_addr + l->l_info[DT_PLTGOT]->d_un.d_ptr + 32);
258 plte += 3 * (reloc - rela_plt);
260 /* Find the displacement from the plt entry to the function. */
262 edisp = (long)(value - (Elf64_Addr)&plte[3]) / 4;
264 if (edisp >= -0x100000 && edisp < 0x100000)
266 /* If we are in range, use br to perfect branch prediction and
267 elide the dependency on the address load. This case happens,
268 e.g., when a shared library call is resolved to the same library. */
271 hi = value - (Elf64_Addr)&plte[0];
273 hi = (hi - lo) >> 16;
275 /* Emit "ldah $27,H($27)" */
276 plte[0] = 0x277b0000 | (hi & 0xffff);
278 /* Emit "lda $27,L($27)" */
279 plte[1] = 0x237b0000 | (lo & 0xffff);
281 /* Emit "br $31,function" */
282 plte[2] = 0xc3e00000 | (edisp & 0x1fffff);
286 /* Don't bother with the hint since we already know the hint is
287 wrong. Eliding it prevents the wrong page from getting pulled
291 hi = got_addr - (Elf64_Addr)&plte[0];
293 hi = (hi - lo) >> 16;
295 /* Emit "ldah $27,H($27)" */
296 plte[0] = 0x277b0000 | (hi & 0xffff);
298 /* Emit "ldq $27,L($27)" */
299 plte[1] = 0xa77b0000 | (lo & 0xffff);
301 /* Emit "jmp $31,($27)" */
302 plte[2] = 0x6bfb0000;
305 /* Flush the instruction cache now that we've diddled. Tag it as
306 modifying memory to checkpoint memory writes during optimization. */
307 asm volatile("call_pal 0x86" : : : "memory");
310 /* Perform the relocation specified by RELOC and SYM (which is fully resolved).
311 MAP is the object containing the reloc. */
313 elf_machine_rela (struct link_map *map,
314 const Elf64_Rela *reloc,
315 const Elf64_Sym *sym)
317 Elf64_Addr * const reloc_addr = (void *)(map->l_addr + reloc->r_offset);
318 unsigned long const r_info = ELF64_R_TYPE (reloc->r_info);
320 #ifndef RTLD_BOOTSTRAP
321 /* This is defined in rtld.c, but nowhere in the static libc.a; make the
322 reference weak so static programs can still link. This declaration
323 cannot be done when compiling rtld.c (i.e. #ifdef RTLD_BOOTSTRAP)
324 because rtld.c contains the common defn for _dl_rtld_map, which is
325 incompatible with a weak decl in the same file. */
326 weak_extern (_dl_rtld_map);
329 /* We cannot use a switch here because we cannot locate the switch
330 jump table until we've self-relocated. */
332 if (r_info == R_ALPHA_RELATIVE)
334 #ifndef RTLD_BOOTSTRAP
335 /* Already done in dynamic linker. */
336 if (map != &_dl_rtld_map)
338 *reloc_addr += map->l_addr;
340 else if (r_info == R_ALPHA_NONE)
344 Elf64_Addr loadbase, sym_value;
346 loadbase = RESOLVE (&sym, (Elf64_Addr)reloc_addr,
347 r_info == R_ALPHA_JMP_SLOT);
348 sym_value = sym ? loadbase + sym->st_value : 0;
350 if (r_info == R_ALPHA_GLOB_DAT)
351 *reloc_addr = sym_value;
352 else if (r_info == R_ALPHA_JMP_SLOT)
354 *reloc_addr = sym_value;
355 elf_alpha_fix_plt (map, reloc, (Elf64_Addr) reloc_addr, sym_value);
357 else if (r_info == R_ALPHA_REFQUAD)
359 sym_value += *reloc_addr;
360 #ifndef RTLD_BOOTSTRAP
361 if (map == &_dl_rtld_map)
363 /* Undo the relocation done here during bootstrapping.
364 Now we will relocate anew, possibly using a binding
365 found in the user program or a loaded library rather
366 than the dynamic linker's built-in definitions used
367 while loading those libraries. */
368 const Elf64_Sym *const dlsymtab
369 = (void *)(map->l_addr + map->l_info[DT_SYMTAB]->d_un.d_ptr);
370 sym_value -= map->l_addr;
371 sym_value -= dlsymtab[ELF64_R_SYM(reloc->r_info)].st_value;
375 sym_value += reloc->r_addend;
376 *reloc_addr = sym_value;
378 else if (r_info == R_ALPHA_COPY)
379 memcpy (reloc_addr, (void *) sym_value, sym->st_size);
381 assert (! "unexpected dynamic reloc type");
386 elf_machine_lazy_rel (struct link_map *map, const Elf64_Rela *reloc)
388 Elf64_Addr * const reloc_addr = (void *)(map->l_addr + reloc->r_offset);
389 unsigned long const r_info = ELF64_R_TYPE (reloc->r_info);
391 if (r_info == R_ALPHA_JMP_SLOT)
393 /* Perform a RELATIVE reloc on the .got entry that transfers
395 *reloc_addr += map->l_addr;
397 else if (r_info == R_ALPHA_NONE)
400 assert (! "unexpected PLT reloc type");