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freebsd-dev/sys/kern/link_elf.c
Doug Rabson fe3db7c7c7 Implement dynamic loading for ELF.
1998-09-11 08:46:15 +00:00

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/*-
* Copyright (c) 1998 Doug Rabson
* All rights reserved.
*
* Redistribution and use in source and binary forms, with or without
* modification, are permitted provided that the following conditions
* are met:
* 1. Redistributions of source code must retain the above copyright
* notice, this list of conditions and the following disclaimer.
* 2. Redistributions in binary form must reproduce the above copyright
* notice, this list of conditions and the following disclaimer in the
* documentation and/or other materials provided with the distribution.
*
* THIS SOFTWARE IS PROVIDED BY THE AUTHOR AND CONTRIBUTORS ``AS IS'' AND
* ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
* IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
* ARE DISCLAIMED. IN NO EVENT SHALL THE AUTHOR OR CONTRIBUTORS BE LIABLE
* FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
* DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
* OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
* HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
* LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
* OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
* SUCH DAMAGE.
*
* $Id: link_elf.c,v 1.1 1998/08/24 08:25:26 dfr Exp $
*/
#include <sys/param.h>
#include <sys/kernel.h>
#include <sys/systm.h>
#include <sys/malloc.h>
#include <sys/proc.h>
#include <sys/namei.h>
#include <sys/fcntl.h>
#include <sys/vnode.h>
#include <sys/linker.h>
#include <machine/elf.h>
#include <vm/vm.h>
#include <vm/vm_prot.h>
#include <vm/vm_param.h>
#include <sys/lock.h>
#include <vm/vm_object.h>
#include <vm/vm_kern.h>
#include <vm/vm_extern.h>
#include <vm/pmap.h>
#include <vm/vm_map.h>
extern int elf_reloc(linker_file_t lf, const Elf_Rela *rela,
const char *sym);
static int link_elf_load_file(const char*, linker_file_t*);
static int link_elf_lookup_symbol(linker_file_t, const char*,
linker_sym_t*);
static void link_elf_symbol_values(linker_file_t, linker_sym_t, linker_symval_t*);
static int link_elf_search_symbol(linker_file_t, caddr_t value,
linker_sym_t* sym, long* diffp);
static void link_elf_unload(linker_file_t);
/*
* The file representing the currently running kernel. This contains
* the global symbol table.
*/
linker_file_t linker_kernel_file;
static struct linker_class_ops link_elf_class_ops = {
link_elf_load_file,
};
static struct linker_file_ops link_elf_file_ops = {
link_elf_lookup_symbol,
link_elf_symbol_values,
link_elf_search_symbol,
link_elf_unload,
};
typedef struct elf_file {
caddr_t address; /* Relocation address */
#ifdef SPARSE_MAPPING
vm_object_t object; /* VM object to hold file pages */
#endif
const Elf_Dyn* dynamic; /* Symbol table etc. */
Elf_Off nbuckets; /* DT_HASH info */
Elf_Off nchains;
const Elf_Off* buckets;
const Elf_Off* chains;
caddr_t hash;
caddr_t strtab; /* DT_STRTAB */
const Elf_Sym* symtab; /* DT_SYMTAB */
Elf_Addr* got; /* DT_PLTGOT */
const Elf_Rel* pltrel; /* DT_JMPREL */
int pltrelsize; /* DT_PLTRELSZ */
const Elf_Rela* pltrela; /* DT_JMPREL */
int pltrelasize; /* DT_PLTRELSZ */
const Elf_Rel* rel; /* DT_REL */
int relsize; /* DT_RELSZ */
const Elf_Rela* rela; /* DT_RELA */
int relasize; /* DT_RELASZ */
} *elf_file_t;
static int parse_dynamic(linker_file_t lf);
static int load_dependancies(linker_file_t lf);
static int relocate_file(linker_file_t lf);
/*
* The kernel symbol table starts here.
*/
extern struct _dynamic _DYNAMIC;
static void
link_elf_init(void* arg)
{
Elf_Dyn* dp = (Elf_Dyn*) &_DYNAMIC;
#if ELF_TARG_CLASS == ELFCLASS32
linker_add_class("elf32", NULL, &link_elf_class_ops);
#else
linker_add_class("elf64", NULL, &link_elf_class_ops);
#endif
if (dp) {
elf_file_t ef;
ef = malloc(sizeof(struct elf_file), M_LINKER, M_NOWAIT);
if (ef == NULL)
panic("link_elf_init: Can't create linker structures for kernel");
ef->address = 0;
#ifdef SPARSE_MAPPING
ef->object = 0;
#endif
ef->dynamic = dp;
linker_kernel_file =
linker_make_file(kernelname, ef, &link_elf_file_ops);
if (linker_kernel_file == NULL)
panic("link_elf_init: Can't create linker structures for kernel");
parse_dynamic(linker_kernel_file);
/*
* XXX there must be a better way of getting these constants.
*/
#ifdef __alpha__
linker_kernel_file->address = (caddr_t) 0xfffffc0000300000;
#else
linker_kernel_file->address = (caddr_t) 0xf0100000;
#endif
linker_kernel_file->size = -(long)linker_kernel_file->address;
linker_current_file = linker_kernel_file;
}
}
SYSINIT(link_elf, SI_SUB_KMEM, SI_ORDER_THIRD, link_elf_init, 0);
static int
parse_dynamic(linker_file_t lf)
{
elf_file_t ef = lf->priv;
const Elf_Dyn *dp;
int plttype = DT_REL;
for (dp = ef->dynamic; dp->d_tag != DT_NULL; dp++) {
switch (dp->d_tag) {
case DT_HASH:
{
/* From src/libexec/rtld-elf/rtld.c */
const Elf_Off *hashtab = (const Elf_Off *)
(ef->address + dp->d_un.d_ptr);
ef->nbuckets = hashtab[0];
ef->nchains = hashtab[1];
ef->buckets = hashtab + 2;
ef->chains = ef->buckets + ef->nbuckets;
break;
}
case DT_STRTAB:
ef->strtab = (caddr_t) (ef->address + dp->d_un.d_ptr);
break;
case DT_SYMTAB:
ef->symtab = (Elf_Sym*) (ef->address + dp->d_un.d_ptr);
break;
case DT_SYMENT:
if (dp->d_un.d_val != sizeof(Elf_Sym))
return ENOEXEC;
break;
case DT_PLTGOT:
ef->got = (Elf_Addr *) (ef->address + dp->d_un.d_ptr);
break;
case DT_REL:
ef->rel = (const Elf_Rel *) (ef->address + dp->d_un.d_ptr);
break;
case DT_RELSZ:
ef->relsize = dp->d_un.d_val;
break;
case DT_RELENT:
if (dp->d_un.d_val != sizeof(Elf_Rel))
return ENOEXEC;
break;
case DT_JMPREL:
ef->pltrel = (const Elf_Rel *) (ef->address + dp->d_un.d_ptr);
break;
case DT_PLTRELSZ:
ef->pltrelsize = dp->d_un.d_val;
break;
case DT_RELA:
ef->rela = (const Elf_Rela *) (ef->address + dp->d_un.d_ptr);
break;
case DT_RELASZ:
ef->relasize = dp->d_un.d_val;
break;
case DT_RELAENT:
if (dp->d_un.d_val != sizeof(Elf_Rela))
return ENOEXEC;
break;
case DT_PLTREL:
plttype = dp->d_un.d_val;
if (plttype != DT_REL && plttype != DT_RELA)
return ENOEXEC;
break;
}
}
if (plttype == DT_RELA) {
ef->pltrela = (const Elf_Rela *) ef->pltrel;
ef->pltrel = NULL;
ef->pltrelasize = ef->pltrelsize;
ef->pltrelsize = 0;
}
return 0;
}
static void
link_elf_error(const char *s)
{
printf("kldload: %s\n", s);
}
static int
link_elf_load_file(const char* filename, linker_file_t* result)
{
struct nameidata nd;
struct proc* p = curproc; /* XXX */
union {
Elf_Ehdr hdr;
char buf[PAGE_SIZE];
} u;
int nbytes, i;
Elf_Phdr *phdr;
Elf_Phdr *phlimit;
Elf_Phdr *segs[2];
int nsegs;
Elf_Phdr *phdyn;
Elf_Phdr *phphdr;
caddr_t mapbase;
size_t mapsize;
Elf_Off base_offset;
Elf_Addr base_vaddr;
Elf_Addr base_vlimit;
caddr_t base_addr;
Elf_Off data_offset;
Elf_Addr data_vaddr;
Elf_Addr data_vlimit;
caddr_t data_addr;
Elf_Addr clear_vaddr;
caddr_t clear_addr;
size_t nclear;
Elf_Addr bss_vaddr;
Elf_Addr bss_vlimit;
caddr_t bss_addr;
int error = 0;
int resid;
elf_file_t ef;
linker_file_t lf;
NDINIT(&nd, LOOKUP, FOLLOW, UIO_SYSSPACE, filename, p);
error = vn_open(&nd, FREAD, 0);
if (error)
return error;
/*
* Read the elf header from the file.
*/
error = vn_rdwr(UIO_READ, nd.ni_vp, (void*) &u, sizeof u, 0,
UIO_SYSSPACE, IO_NODELOCKED, p->p_ucred, &resid, p);
nbytes = sizeof u - resid;
if (error)
goto out;
if (!IS_ELF(u.hdr)) {
error = ENOEXEC;
goto out;
}
if (u.hdr.e_ident[EI_CLASS] != ELF_TARG_CLASS
|| u.hdr.e_ident[EI_DATA] != ELF_TARG_DATA) {
link_elf_error("Unsupported file layout");
error = ENOEXEC;
goto out;
}
if (u.hdr.e_ident[EI_VERSION] != EV_CURRENT
|| u.hdr.e_version != EV_CURRENT) {
link_elf_error("Unsupported file version");
error = ENOEXEC;
goto out;
}
if (u.hdr.e_type != ET_EXEC && u.hdr.e_type != ET_DYN) {
link_elf_error("Unsupported file type");
error = ENOEXEC;
goto out;
}
if (u.hdr.e_machine != ELF_TARG_MACH) {
link_elf_error("Unsupported machine");
error = ENOEXEC;
goto out;
}
if (!ELF_MACHINE_OK(u.hdr.e_machine)) {
link_elf_error("Incompatibile elf machine type");
error = ENOEXEC;
goto out;
}
/*
* We rely on the program header being in the first page. This is
* not strictly required by the ABI specification, but it seems to
* always true in practice. And, it simplifies things considerably.
*/
if (!((u.hdr.e_phentsize == sizeof(Elf_Phdr))
|| (u.hdr.e_phoff + u.hdr.e_phnum*sizeof(Elf_Phdr) <= PAGE_SIZE)
|| (u.hdr.e_phoff + u.hdr.e_phnum*sizeof(Elf_Phdr) <= nbytes)))
link_elf_error("Unreadable program headers");
/*
* Scan the program header entries, and save key information.
*
* We rely on there being exactly two load segments, text and data,
* in that order.
*/
phdr = (Elf_Phdr *) (u.buf + u.hdr.e_phoff);
phlimit = phdr + u.hdr.e_phnum;
nsegs = 0;
phdyn = NULL;
phphdr = NULL;
while (phdr < phlimit) {
switch (phdr->p_type) {
case PT_LOAD:
if (nsegs == 2) {
link_elf_error("Too many sections");
error = ENOEXEC;
goto out;
}
segs[nsegs] = phdr;
++nsegs;
break;
case PT_PHDR:
phphdr = phdr;
break;
case PT_DYNAMIC:
phdyn = phdr;
break;
}
++phdr;
}
if (phdyn == NULL) {
link_elf_error("Object is not dynamically-linked");
error = ENOEXEC;
goto out;
}
/*
* Allocate the entire address space of the object, to stake out our
* contiguous region, and to establish the base address for relocation.
*/
base_offset = trunc_page(segs[0]->p_offset);
base_vaddr = trunc_page(segs[0]->p_vaddr);
base_vlimit = round_page(segs[1]->p_vaddr + segs[1]->p_memsz);
mapsize = base_vlimit - base_vaddr;
ef = malloc(sizeof(struct elf_file), M_LINKER, M_WAITOK);
#ifdef SPARSE_MAPPING
ef->object = vm_object_allocate(OBJT_DEFAULT, mapsize >> PAGE_SHIFT);
if (ef->object == NULL) {
free(ef, M_LINKER);
error = ENOMEM;
goto out;
}
vm_object_reference(ef->object);
ef->address = (caddr_t) vm_map_min(kernel_map);
error = vm_map_find(kernel_map, ef->object, 0,
(vm_offset_t *) &ef->address,
mapsize, 1,
VM_PROT_ALL, VM_PROT_ALL, 0);
if (error) {
vm_object_deallocate(ef->object);
free(ef, M_LINKER);
goto out;
}
#else
ef->address = malloc(mapsize, M_LINKER, M_WAITOK);
#endif
mapbase = ef->address;
/*
* Read the text and data sections and zero the bss.
*/
for (i = 0; i < 2; i++) {
caddr_t segbase = mapbase + segs[i]->p_vaddr - base_vaddr;
error = vn_rdwr(UIO_READ, nd.ni_vp,
segbase, segs[i]->p_filesz, segs[i]->p_offset,
UIO_SYSSPACE, IO_NODELOCKED, p->p_ucred, &resid, p);
if (error) {
#ifdef SPARSE_MAPPING
vm_map_remove(kernel_map, (vm_offset_t) ef->address,
(vm_offset_t) ef->address
+ (ef->object->size << PAGE_SHIFT));
vm_object_deallocate(ef->object);
#else
free(ef->address, M_LINKER);
#endif
free(ef, M_LINKER);
goto out;
}
bzero(segbase + segs[i]->p_filesz,
segs[i]->p_memsz - segs[i]->p_filesz);
#ifdef SPARSE_MAPPING
/*
* Wire down the pages
*/
vm_map_pageable(kernel_map,
(vm_offset_t) segbase,
(vm_offset_t) segbase + segs[i]->p_memsz,
FALSE);
#endif
}
ef->dynamic = (const Elf_Dyn *) (mapbase + phdyn->p_vaddr - base_vaddr);
lf = linker_make_file(filename, ef, &link_elf_file_ops);
if (lf == NULL) {
#ifdef SPARSE_MAPPING
vm_map_remove(kernel_map, (vm_offset_t) ef->address,
(vm_offset_t) ef->address
+ (ef->object->size << PAGE_SHIFT));
vm_object_deallocate(ef->object);
#else
free(ef->address, M_LINKER);
#endif
free(ef, M_LINKER);
error = ENOMEM;
goto out;
}
lf->address = ef->address;
lf->size = mapsize;
if ((error = parse_dynamic(lf)) != 0
|| (error = load_dependancies(lf)) != 0
|| (error = relocate_file(lf)) != 0) {
linker_file_unload(lf);
goto out;
}
*result = lf;
out:
VOP_UNLOCK(nd.ni_vp, 0, p);
vn_close(nd.ni_vp, FREAD, p->p_ucred, p);
return error;
}
static void
link_elf_unload(linker_file_t file)
{
elf_file_t ef = file->priv;
if (ef) {
#ifdef SPARSE_MAPPING
if (ef->object) {
vm_map_remove(kernel_map, (vm_offset_t) ef->address,
(vm_offset_t) ef->address
+ (ef->object->size << PAGE_SHIFT));
vm_object_deallocate(ef->object);
}
#else
free(ef->address, M_LINKER);
#endif
free(ef, M_LINKER);
}
}
static int
load_dependancies(linker_file_t lf)
{
elf_file_t ef = lf->priv;
linker_file_t lfdep;
char* name;
char* filename = 0;
const Elf_Dyn *dp;
int error = 0;
/*
* All files are dependant on /kernel.
*/
linker_kernel_file->refs++;
linker_file_add_dependancy(lf, linker_kernel_file);
for (dp = ef->dynamic; dp->d_tag != DT_NULL; dp++) {
if (dp->d_tag == DT_NEEDED) {
name = ef->strtab + dp->d_un.d_val;
/*
* Prepend pathname if dep is not an absolute filename.
*/
if (name[0] != '/') {
char* p;
if (!filename) {
filename = malloc(MAXPATHLEN, M_TEMP, M_WAITOK);
if (!filename) {
error = ENOMEM;
goto out;
}
}
p = lf->filename + strlen(lf->filename) - 1;
while (p >= lf->filename && *p != '/')
p--;
if (p >= lf->filename) {
strncpy(filename, lf->filename, p - lf->filename);
filename[p - lf->filename] = '\0';
strcat(filename, "/");
strcat(filename, name);
name = filename;
}
}
error = linker_load_file(name, &lfdep);
if (error)
goto out;
error = linker_file_add_dependancy(lf, lfdep);
if (error)
goto out;
}
}
out:
if (filename)
free(filename, M_TEMP);
return error;
}
static const char *
symbol_name(elf_file_t ef, const Elf_Rela *rela)
{
const Elf_Sym *ref;
if (ELF_R_SYM(rela->r_info)) {
ref = ef->symtab + ELF_R_SYM(rela->r_info);
return ef->strtab + ref->st_name;
} else
return NULL;
}
static int
relocate_file(linker_file_t lf)
{
elf_file_t ef = lf->priv;
const Elf_Rel *rellim;
const Elf_Rel *rel;
const Elf_Rela *relalim;
const Elf_Rela *rela;
/* Perform relocations without addend if there are any: */
rellim = (const Elf_Rel *) ((caddr_t) ef->rel + ef->relsize);
for (rel = ef->rel; ef->rel != NULL && rel < rellim; rel++) {
Elf_Rela locrela;
locrela.r_info = rel->r_info;
locrela.r_offset = rel->r_offset;
locrela.r_addend = 0;
if (elf_reloc(lf, &locrela, symbol_name(ef, &locrela)))
return ENOENT;
}
/* Perform relocations with addend if there are any: */
relalim = (const Elf_Rela *) ((caddr_t) ef->rela + ef->relasize);
for (rela = ef->rela; ef->rela != NULL && rela < relalim; rela++) {
if (elf_reloc(lf, rela, symbol_name(ef, rela)))
return ENOENT;
}
/* Perform PLT relocations without addend if there are any: */
rellim = (const Elf_Rel *) ((caddr_t) ef->pltrel + ef->pltrelsize);
for (rel = ef->pltrel; ef->pltrel != NULL && rel < rellim; rel++) {
Elf_Rela locrela;
locrela.r_info = rel->r_info;
locrela.r_offset = rel->r_offset;
locrela.r_addend = 0;
if (elf_reloc(lf, &locrela, symbol_name(ef, &locrela)))
return ENOENT;
}
/* Perform relocations with addend if there are any: */
relalim = (const Elf_Rela *) ((caddr_t) ef->pltrela + ef->pltrelasize);
for (rela = ef->pltrela; ef->pltrela != NULL && rela < relalim; rela++) {
if (elf_reloc(lf, rela, symbol_name(ef, rela)))
return ENOENT;
}
return 0;
}
/*
* Hash function for symbol table lookup. Don't even think about changing
* this. It is specified by the System V ABI.
*/
static unsigned long
elf_hash(const char *name)
{
const unsigned char *p = (const unsigned char *) name;
unsigned long h = 0;
unsigned long g;
while (*p != '\0') {
h = (h << 4) + *p++;
if ((g = h & 0xf0000000) != 0)
h ^= g >> 24;
h &= ~g;
}
return h;
}
int
link_elf_lookup_symbol(linker_file_t lf, const char* name, linker_sym_t* sym)
{
elf_file_t ef = lf->priv;
unsigned long symnum;
const Elf_Sym* es;
unsigned long hash;
int i;
hash = elf_hash(name);
symnum = ef->buckets[hash % ef->nbuckets];
while (symnum != STN_UNDEF) {
const Elf_Sym *symp;
const char *strp;
if (symnum >= ef->nchains) {
printf("link_elf_lookup_symbol: corrupt symbol table\n");
return ENOENT;
}
symp = ef->symtab + symnum;
if (symp->st_name == 0) {
printf("link_elf_lookup_symbol: corrupt symbol table\n");
return ENOENT;
}
strp = ef->strtab + symp->st_name;
if (strcmp(name, strp) == 0) {
if (symp->st_shndx != SHN_UNDEF ||
(symp->st_value != 0 &&
ELF_ST_TYPE(symp->st_info) == STT_FUNC)) {
*sym = (linker_sym_t) symp;
return 0;
} else
return ENOENT;
}
symnum = ef->chains[symnum];
}
return ENOENT;
}
static void
link_elf_symbol_values(linker_file_t lf, linker_sym_t sym, linker_symval_t* symval)
{
elf_file_t ef = lf->priv;
Elf_Sym* es = (Elf_Sym*) sym;
symval->name = ef->strtab + es->st_name;
symval->value = (caddr_t) ef->address + es->st_value;
symval->size = es->st_size;
}
static int
link_elf_search_symbol(linker_file_t lf, caddr_t value,
linker_sym_t* sym, long* diffp)
{
elf_file_t ef = lf->priv;
u_long off = (u_long) value;
u_long diff = off;
int symcount = ef->nchains;
const Elf_Sym* es;
const Elf_Sym* best = 0;
int i;
for (i = 0, es = ef->symtab; i < ef->nchains; i++, es++) {
if (es->st_name == 0)
continue;
if (off >= es->st_value) {
if (off - es->st_value < diff) {
diff = off - es->st_value;
best = es;
if (diff == 0)
break;
} else if (off - es->st_value == diff) {
best = es;
}
}
}
if (best == 0)
*diffp = off;
else
*diffp = diff;
*sym = (linker_sym_t) best;
return 0;
}
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