2 * Copyright (c) 1998 Michael Smith <msmith@freebsd.org>
3 * Copyright (c) 1998 Peter Wemm <peter@freebsd.org>
6 * Redistribution and use in source and binary forms, with or without
7 * modification, are permitted provided that the following conditions
9 * 1. Redistributions of source code must retain the above copyright
10 * notice, this list of conditions and the following disclaimer.
11 * 2. Redistributions in binary form must reproduce the above copyright
12 * notice, this list of conditions and the following disclaimer in the
13 * documentation and/or other materials provided with the distribution.
15 * THIS SOFTWARE IS PROVIDED BY THE AUTHOR AND CONTRIBUTORS ``AS IS'' AND
16 * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
17 * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
18 * ARE DISCLAIMED. IN NO EVENT SHALL THE AUTHOR OR CONTRIBUTORS BE LIABLE
19 * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
20 * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
21 * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
22 * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
23 * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
24 * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
28 #include <sys/cdefs.h>
29 __FBSDID("$FreeBSD$");
31 #include <sys/param.h>
33 #include <sys/linker.h>
34 #include <sys/module.h>
35 #include <sys/stdint.h>
37 #include <machine/elf.h>
42 #include "bootstrap.h"
44 #define COPYOUT(s,d,l) archsw.arch_copyout((vm_offset_t)(s), d, l)
46 #if defined(__i386__) && __ELF_WORD_SIZE == 64
49 #define ELF_TARG_CLASS ELFCLASS64
50 #define ELF_TARG_MACH EM_X86_64
53 typedef struct elf_file {
75 static int __elfN(loadimage)(struct preloaded_file *mp, elf_file_t ef, u_int64_t loadaddr);
76 static int __elfN(lookup_symbol)(struct preloaded_file *mp, elf_file_t ef, const char* name, Elf_Sym* sym);
77 static int __elfN(reloc_ptr)(struct preloaded_file *mp, elf_file_t ef,
78 Elf_Addr p, void *val, size_t len);
79 static int __elfN(parse_modmetadata)(struct preloaded_file *mp, elf_file_t ef);
80 static symaddr_fn __elfN(symaddr);
81 static char *fake_modname(const char *name);
83 const char *__elfN(kerneltype) = "elf kernel";
84 const char *__elfN(moduletype) = "elf module";
86 u_int64_t __elfN(relocation_offset) = 0;
89 * Attempt to load the file (file) as an ELF module. It will be stored at
90 * (dest), and a pointer to a module structure describing the loaded object
91 * will be saved in (result).
94 __elfN(loadfile)(char *filename, u_int64_t dest, struct preloaded_file **result)
96 struct preloaded_file *fp, *kfp;
103 bzero(&ef, sizeof(struct elf_file));
106 * Open the image, read and validate the ELF header
108 if (filename == NULL) /* can't handle nameless */
110 if ((ef.fd = open(filename, O_RDONLY)) == -1)
112 ef.firstpage = malloc(PAGE_SIZE);
113 if (ef.firstpage == NULL) {
117 bytes_read = read(ef.fd, ef.firstpage, PAGE_SIZE);
118 ef.firstlen = (size_t)bytes_read;
119 if (bytes_read < 0 || ef.firstlen <= sizeof(Elf_Ehdr)) {
120 err = EFTYPE; /* could be EIO, but may be small file */
123 ehdr = ef.ehdr = (Elf_Ehdr *)ef.firstpage;
126 if (!IS_ELF(*ehdr)) {
130 if (ehdr->e_ident[EI_CLASS] != ELF_TARG_CLASS || /* Layout ? */
131 ehdr->e_ident[EI_DATA] != ELF_TARG_DATA ||
132 ehdr->e_ident[EI_VERSION] != EV_CURRENT || /* Version ? */
133 ehdr->e_version != EV_CURRENT ||
134 ehdr->e_machine != ELF_TARG_MACH) { /* Machine ? */
141 * Check to see what sort of module we are.
143 kfp = file_findfile(NULL, NULL);
144 if (ehdr->e_type == ET_DYN) {
145 /* Looks like a kld module */
147 printf("elf" __XSTRING(__ELF_WORD_SIZE) "_loadfile: can't load module before kernel\n");
151 if (strcmp(__elfN(kerneltype), kfp->f_type)) {
152 printf("elf" __XSTRING(__ELF_WORD_SIZE) "_loadfile: can't load module with kernel type '%s'\n", kfp->f_type);
156 /* Looks OK, got ahead */
159 } else if (ehdr->e_type == ET_EXEC) {
160 /* Looks like a kernel */
162 printf("elf" __XSTRING(__ELF_WORD_SIZE) "_loadfile: kernel already loaded\n");
167 * Calculate destination address based on kernel entrypoint
169 dest = (ehdr->e_entry & ~PAGE_MASK);
171 printf("elf" __XSTRING(__ELF_WORD_SIZE) "_loadfile: not a kernel (maybe static binary?)\n");
182 if (archsw.arch_loadaddr != NULL)
183 dest = archsw.arch_loadaddr(LOAD_ELF, ehdr, dest);
185 dest = roundup(dest, PAGE_SIZE);
188 * Ok, we think we should handle this.
192 printf("elf" __XSTRING(__ELF_WORD_SIZE) "_loadfile: cannot allocate module info\n");
197 setenv("kernelname", filename, 1);
198 fp->f_name = strdup(filename);
199 fp->f_type = strdup(ef.kernel ? __elfN(kerneltype) : __elfN(moduletype));
203 printf("%s entry at 0x%jx\n", filename, (uintmax_t)ehdr->e_entry);
205 printf("%s ", filename);
208 fp->f_size = __elfN(loadimage)(fp, &ef, dest);
209 if (fp->f_size == 0 || fp->f_addr == 0)
212 /* save exec header as metadata */
213 file_addmetadata(fp, MODINFOMD_ELFHDR, sizeof(*ehdr), ehdr);
215 /* Load OK, return module pointer */
216 *result = (struct preloaded_file *)fp;
232 * With the file (fd) open on the image, and (ehdr) containing
233 * the Elf header, load the image at (off)
236 __elfN(loadimage)(struct preloaded_file *fp, elf_file_t ef, u_int64_t off)
241 Elf_Phdr *phdr, *php;
245 vm_offset_t firstaddr;
246 vm_offset_t lastaddr;
262 firstaddr = lastaddr = 0;
265 #if defined(__i386__) || defined(__amd64__)
266 #if __ELF_WORD_SIZE == 64
267 off = - (off & 0xffffffffff000000ull);/* x86_64 relocates after locore */
269 off = - (off & 0xff000000u); /* i386 relocates after locore */
271 #elif defined(__powerpc__)
273 * On the purely virtual memory machines like e500, the kernel is
274 * linked against its final VA range, which is most often not
275 * available at the loader stage, but only after kernel initializes
276 * and completes its VM settings. In such cases we cannot use p_vaddr
277 * field directly to load ELF segments, but put them at some
278 * 'load-time' locations.
280 if (off & 0xf0000000u) {
281 off = -(off & 0xf0000000u);
283 * XXX the physical load address should not be hardcoded. Note
284 * that the Book-E kernel assumes that it's loaded at a 16MB
285 * boundary for now...
288 ehdr->e_entry += off;
290 printf("Converted entry 0x%08x\n", ehdr->e_entry);
294 #elif defined(__arm__)
296 * The elf headers in some kernels specify virtual addresses in all
297 * header fields. More recently, the e_entry and p_paddr fields are the
298 * proper physical addresses. Even when the p_paddr fields are correct,
299 * the MI code below uses the p_vaddr fields with an offset added for
300 * loading (doing so is arguably wrong). To make loading work, we need
301 * an offset that represents the difference between physical and virtual
302 * addressing. ARM kernels are always linked at 0xCnnnnnnn. Depending
303 * on the headers, the offset value passed in may be physical or virtual
304 * (because it typically comes from e_entry), but we always replace
305 * whatever is passed in with the va<->pa offset. On the other hand, we
306 * always remove the high-order part of the entry address whether it's
307 * physical or virtual, because it will be adjusted later for the actual
308 * physical entry point based on where the image gets loaded.
311 ehdr->e_entry &= ~0xf0000000;
313 printf("ehdr->e_entry 0x%08x, va<->pa off %llx\n", ehdr->e_entry, off);
316 off = 0; /* other archs use direct mapped kernels */
318 __elfN(relocation_offset) = off;
322 if ((ehdr->e_phoff + ehdr->e_phnum * sizeof(*phdr)) > ef->firstlen) {
323 printf("elf" __XSTRING(__ELF_WORD_SIZE) "_loadimage: program header not within first page\n");
326 phdr = (Elf_Phdr *)(ef->firstpage + ehdr->e_phoff);
328 for (i = 0; i < ehdr->e_phnum; i++) {
329 /* We want to load PT_LOAD segments only.. */
330 if (phdr[i].p_type != PT_LOAD)
334 printf("Segment: 0x%lx@0x%lx -> 0x%lx-0x%lx",
335 (long)phdr[i].p_filesz, (long)phdr[i].p_offset,
336 (long)(phdr[i].p_vaddr + off),
337 (long)(phdr[i].p_vaddr + off + phdr[i].p_memsz - 1));
339 if ((phdr[i].p_flags & PF_W) == 0) {
340 printf("text=0x%lx ", (long)phdr[i].p_filesz);
342 printf("data=0x%lx", (long)phdr[i].p_filesz);
343 if (phdr[i].p_filesz < phdr[i].p_memsz)
344 printf("+0x%lx", (long)(phdr[i].p_memsz -phdr[i].p_filesz));
349 if (ef->firstlen > phdr[i].p_offset) {
350 fpcopy = ef->firstlen - phdr[i].p_offset;
351 archsw.arch_copyin(ef->firstpage + phdr[i].p_offset,
352 phdr[i].p_vaddr + off, fpcopy);
354 if (phdr[i].p_filesz > fpcopy) {
355 if (kern_pread(ef->fd, phdr[i].p_vaddr + off + fpcopy,
356 phdr[i].p_filesz - fpcopy, phdr[i].p_offset + fpcopy) != 0) {
357 printf("\nelf" __XSTRING(__ELF_WORD_SIZE)
358 "_loadimage: read failed\n");
362 /* clear space from oversized segments; eg: bss */
363 if (phdr[i].p_filesz < phdr[i].p_memsz) {
365 printf(" (bss: 0x%lx-0x%lx)",
366 (long)(phdr[i].p_vaddr + off + phdr[i].p_filesz),
367 (long)(phdr[i].p_vaddr + off + phdr[i].p_memsz - 1));
370 kern_bzero(phdr[i].p_vaddr + off + phdr[i].p_filesz,
371 phdr[i].p_memsz - phdr[i].p_filesz);
377 if (archsw.arch_loadseg != NULL)
378 archsw.arch_loadseg(ehdr, phdr + i, off);
380 if (firstaddr == 0 || firstaddr > (phdr[i].p_vaddr + off))
381 firstaddr = phdr[i].p_vaddr + off;
382 if (lastaddr == 0 || lastaddr < (phdr[i].p_vaddr + off + phdr[i].p_memsz))
383 lastaddr = phdr[i].p_vaddr + off + phdr[i].p_memsz;
385 lastaddr = roundup(lastaddr, sizeof(long));
388 * Get the section headers. We need this for finding the .ctors
389 * section as well as for loading any symbols. Both may be hard
390 * to do if reading from a .gz file as it involves seeking. I
391 * think the rule is going to have to be that you must strip a
392 * file to remove symbols before gzipping it.
394 chunk = ehdr->e_shnum * ehdr->e_shentsize;
395 if (chunk == 0 || ehdr->e_shoff == 0)
397 shdr = alloc_pread(ef->fd, ehdr->e_shoff, chunk);
399 printf("\nelf" __XSTRING(__ELF_WORD_SIZE)
400 "_loadimage: failed to read section headers");
403 file_addmetadata(fp, MODINFOMD_SHDR, chunk, shdr);
406 * Read the section string table and look for the .ctors section.
407 * We need to tell the kernel where it is so that it can call the
410 chunk = shdr[ehdr->e_shstrndx].sh_size;
412 shstr = alloc_pread(ef->fd, shdr[ehdr->e_shstrndx].sh_offset, chunk);
414 for (i = 0; i < ehdr->e_shnum; i++) {
415 if (strcmp(shstr + shdr[i].sh_name, ".ctors") != 0)
417 ctors = shdr[i].sh_addr;
418 file_addmetadata(fp, MODINFOMD_CTORS_ADDR, sizeof(ctors),
420 size = shdr[i].sh_size;
421 file_addmetadata(fp, MODINFOMD_CTORS_SIZE, sizeof(size),
430 * Now load any symbols.
434 for (i = 0; i < ehdr->e_shnum; i++) {
435 if (shdr[i].sh_type != SHT_SYMTAB)
437 for (j = 0; j < ehdr->e_phnum; j++) {
438 if (phdr[j].p_type != PT_LOAD)
440 if (shdr[i].sh_offset >= phdr[j].p_offset &&
441 (shdr[i].sh_offset + shdr[i].sh_size <=
442 phdr[j].p_offset + phdr[j].p_filesz)) {
443 shdr[i].sh_offset = 0;
448 if (shdr[i].sh_offset == 0 || shdr[i].sh_size == 0)
449 continue; /* alread loaded in a PT_LOAD above */
450 /* Save it for loading below */
452 symstrindex = shdr[i].sh_link;
454 if (symtabindex < 0 || symstrindex < 0)
457 /* Ok, committed to a load. */
462 for (i = symtabindex; i >= 0; i = symstrindex) {
466 switch(shdr[i].sh_type) {
467 case SHT_SYMTAB: /* Symbol table */
470 case SHT_STRTAB: /* String table */
479 size = shdr[i].sh_size;
480 archsw.arch_copyin(&size, lastaddr, sizeof(size));
481 lastaddr += sizeof(size);
484 printf("\n%s: 0x%jx@0x%jx -> 0x%jx-0x%jx", secname,
485 (uintmax_t)shdr[i].sh_size, (uintmax_t)shdr[i].sh_offset,
486 (uintmax_t)lastaddr, (uintmax_t)(lastaddr + shdr[i].sh_size));
488 if (i == symstrindex)
490 printf("0x%lx+0x%lx", (long)sizeof(size), (long)size);
493 if (lseek(ef->fd, (off_t)shdr[i].sh_offset, SEEK_SET) == -1) {
494 printf("\nelf" __XSTRING(__ELF_WORD_SIZE) "_loadimage: could not seek for symbols - skipped!");
499 result = archsw.arch_readin(ef->fd, lastaddr, shdr[i].sh_size);
500 if (result < 0 || (size_t)result != shdr[i].sh_size) {
501 printf("\nelf" __XSTRING(__ELF_WORD_SIZE) "_loadimage: could not read symbols - skipped! (%ju != %ju)", (uintmax_t)result,
502 (uintmax_t)shdr[i].sh_size);
507 /* Reset offsets relative to ssym */
508 lastaddr += shdr[i].sh_size;
509 lastaddr = roundup(lastaddr, sizeof(size));
510 if (i == symtabindex)
512 else if (i == symstrindex)
520 file_addmetadata(fp, MODINFOMD_SSYM, sizeof(ssym), &ssym);
521 file_addmetadata(fp, MODINFOMD_ESYM, sizeof(esym), &esym);
526 ret = lastaddr - firstaddr;
527 fp->f_addr = firstaddr;
530 for (i = 0; i < ehdr->e_phnum; i++) {
531 if (phdr[i].p_type == PT_DYNAMIC) {
534 file_addmetadata(fp, MODINFOMD_DYNAMIC, sizeof(adp), &adp);
539 if (php == NULL) /* this is bad, we cannot get to symbols or _DYNAMIC */
542 ndp = php->p_filesz / sizeof(Elf_Dyn);
545 dp = malloc(php->p_filesz);
548 archsw.arch_copyout(php->p_vaddr + off, dp, php->p_filesz);
551 for (i = 0; i < ndp; i++) {
552 if (dp[i].d_tag == 0)
554 switch (dp[i].d_tag) {
556 ef->hashtab = (Elf_Hashelt*)(uintptr_t)(dp[i].d_un.d_ptr + off);
559 ef->strtab = (char *)(uintptr_t)(dp[i].d_un.d_ptr + off);
562 ef->strsz = dp[i].d_un.d_val;
565 ef->symtab = (Elf_Sym*)(uintptr_t)(dp[i].d_un.d_ptr + off);
568 ef->rel = (Elf_Rel *)(uintptr_t)(dp[i].d_un.d_ptr + off);
571 ef->relsz = dp[i].d_un.d_val;
574 ef->rela = (Elf_Rela *)(uintptr_t)(dp[i].d_un.d_ptr + off);
577 ef->relasz = dp[i].d_un.d_val;
583 if (ef->hashtab == NULL || ef->symtab == NULL ||
584 ef->strtab == NULL || ef->strsz == 0)
586 COPYOUT(ef->hashtab, &ef->nbuckets, sizeof(ef->nbuckets));
587 COPYOUT(ef->hashtab + 1, &ef->nchains, sizeof(ef->nchains));
588 ef->buckets = ef->hashtab + 2;
589 ef->chains = ef->buckets + ef->nbuckets;
590 if (__elfN(parse_modmetadata)(fp, ef) == 0)
593 if (ef->kernel) /* kernel must not depend on anything */
604 static char invalid_name[] = "bad";
607 fake_modname(const char *name)
613 sp = strrchr(name, '/');
618 ep = strrchr(name, '.');
622 ep = invalid_name + sizeof(invalid_name) - 1;
625 ep = name + strlen(name);
627 fp = malloc(len + 1);
635 #if (defined(__i386__) || defined(__powerpc__)) && __ELF_WORD_SIZE == 64
636 struct mod_metadata64 {
637 int md_version; /* structure version MDTV_* */
638 int md_type; /* type of entry MDT_* */
639 u_int64_t md_data; /* specific data */
640 u_int64_t md_cval; /* common string label */
643 #if defined(__amd64__) && __ELF_WORD_SIZE == 32
644 struct mod_metadata32 {
645 int md_version; /* structure version MDTV_* */
646 int md_type; /* type of entry MDT_* */
647 u_int32_t md_data; /* specific data */
648 u_int32_t md_cval; /* common string label */
653 __elfN(parse_modmetadata)(struct preloaded_file *fp, elf_file_t ef)
655 struct mod_metadata md;
656 #if (defined(__i386__) || defined(__powerpc__)) && __ELF_WORD_SIZE == 64
657 struct mod_metadata64 md64;
658 #elif defined(__amd64__) && __ELF_WORD_SIZE == 32
659 struct mod_metadata32 md32;
661 struct mod_depend *mdepend;
662 struct mod_version mver;
665 int error, modcnt, minfolen;
666 Elf_Addr v, p, p_stop;
668 if (__elfN(lookup_symbol)(fp, ef, "__start_set_modmetadata_set", &sym) != 0)
670 p = sym.st_value + ef->off;
671 if (__elfN(lookup_symbol)(fp, ef, "__stop_set_modmetadata_set", &sym) != 0)
673 p_stop = sym.st_value + ef->off;
677 COPYOUT(p, &v, sizeof(v));
678 error = __elfN(reloc_ptr)(fp, ef, p, &v, sizeof(v));
679 if (error == EOPNOTSUPP)
683 #if (defined(__i386__) || defined(__powerpc__)) && __ELF_WORD_SIZE == 64
684 COPYOUT(v, &md64, sizeof(md64));
685 error = __elfN(reloc_ptr)(fp, ef, v, &md64, sizeof(md64));
686 if (error == EOPNOTSUPP) {
687 md64.md_cval += ef->off;
688 md64.md_data += ef->off;
689 } else if (error != 0)
691 md.md_version = md64.md_version;
692 md.md_type = md64.md_type;
693 md.md_cval = (const char *)(uintptr_t)md64.md_cval;
694 md.md_data = (void *)(uintptr_t)md64.md_data;
695 #elif defined(__amd64__) && __ELF_WORD_SIZE == 32
696 COPYOUT(v, &md32, sizeof(md32));
697 error = __elfN(reloc_ptr)(fp, ef, v, &md32, sizeof(md32));
698 if (error == EOPNOTSUPP) {
699 md32.md_cval += ef->off;
700 md32.md_data += ef->off;
701 } else if (error != 0)
703 md.md_version = md32.md_version;
704 md.md_type = md32.md_type;
705 md.md_cval = (const char *)(uintptr_t)md32.md_cval;
706 md.md_data = (void *)(uintptr_t)md32.md_data;
708 COPYOUT(v, &md, sizeof(md));
709 error = __elfN(reloc_ptr)(fp, ef, v, &md, sizeof(md));
710 if (error == EOPNOTSUPP) {
711 md.md_cval += ef->off;
712 md.md_data += ef->off;
713 } else if (error != 0)
716 p += sizeof(Elf_Addr);
719 if (ef->kernel) /* kernel must not depend on anything */
721 s = strdupout((vm_offset_t)md.md_cval);
722 minfolen = sizeof(*mdepend) + strlen(s) + 1;
723 mdepend = malloc(minfolen);
726 COPYOUT((vm_offset_t)md.md_data, mdepend, sizeof(*mdepend));
727 strcpy((char*)(mdepend + 1), s);
729 file_addmetadata(fp, MODINFOMD_DEPLIST, minfolen, mdepend);
733 s = strdupout((vm_offset_t)md.md_cval);
734 COPYOUT((vm_offset_t)md.md_data, &mver, sizeof(mver));
735 file_addmodule(fp, s, mver.mv_version, NULL);
742 s = fake_modname(fp->f_name);
743 file_addmodule(fp, s, 1, NULL);
750 elf_hash(const char *name)
752 const unsigned char *p = (const unsigned char *) name;
758 if ((g = h & 0xf0000000) != 0)
765 static const char __elfN(bad_symtable)[] = "elf" __XSTRING(__ELF_WORD_SIZE) "_lookup_symbol: corrupt symbol table\n";
767 __elfN(lookup_symbol)(struct preloaded_file *fp, elf_file_t ef, const char* name,
775 hash = elf_hash(name);
776 COPYOUT(&ef->buckets[hash % ef->nbuckets], &symnum, sizeof(symnum));
778 while (symnum != STN_UNDEF) {
779 if (symnum >= ef->nchains) {
780 printf(__elfN(bad_symtable));
784 COPYOUT(ef->symtab + symnum, &sym, sizeof(sym));
785 if (sym.st_name == 0) {
786 printf(__elfN(bad_symtable));
790 strp = strdupout((vm_offset_t)(ef->strtab + sym.st_name));
791 if (strcmp(name, strp) == 0) {
793 if (sym.st_shndx != SHN_UNDEF ||
794 (sym.st_value != 0 &&
795 ELF_ST_TYPE(sym.st_info) == STT_FUNC)) {
802 COPYOUT(&ef->chains[symnum], &symnum, sizeof(symnum));
808 * Apply any intra-module relocations to the value. p is the load address
809 * of the value and val/len is the value to be modified. This does NOT modify
810 * the image in-place, because this is done by kern_linker later on.
812 * Returns EOPNOTSUPP if no relocation method is supplied.
815 __elfN(reloc_ptr)(struct preloaded_file *mp, elf_file_t ef,
816 Elf_Addr p, void *val, size_t len)
824 * The kernel is already relocated, but we still want to apply
825 * offset adjustments.
830 for (n = 0; n < ef->relsz / sizeof(r); n++) {
831 COPYOUT(ef->rel + n, &r, sizeof(r));
833 error = __elfN(reloc)(ef, __elfN(symaddr), &r, ELF_RELOC_REL,
834 ef->off, p, val, len);
838 for (n = 0; n < ef->relasz / sizeof(a); n++) {
839 COPYOUT(ef->rela + n, &a, sizeof(a));
841 error = __elfN(reloc)(ef, __elfN(symaddr), &a, ELF_RELOC_RELA,
842 ef->off, p, val, len);
851 __elfN(symaddr)(struct elf_file *ef, Elf_Size symidx)
854 /* Symbol lookup by index not required here. */