quite a few enhancements and bug fixes. There are still some known deficiencies, but it should be adequate to get us started with ELF. Submitted by: John Polstra <jdp@polstra.com>
251 lines
7.6 KiB
C
251 lines
7.6 KiB
C
/*-
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* Copyright 1996-1998 John D. Polstra.
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* All rights reserved.
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*
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* Redistribution and use in source and binary forms, with or without
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* modification, are permitted provided that the following conditions
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* are met:
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* 1. Redistributions of source code must retain the above copyright
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* notice, this list of conditions and the following disclaimer.
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* 2. Redistributions in binary form must reproduce the above copyright
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* notice, this list of conditions and the following disclaimer in the
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* documentation and/or other materials provided with the distribution.
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*
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* THIS SOFTWARE IS PROVIDED BY THE AUTHOR ``AS IS'' AND ANY EXPRESS OR
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* IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES
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* OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED.
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* IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR ANY DIRECT, INDIRECT,
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* INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT
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* NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
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* DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
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* THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
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* (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF
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* THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
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*
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* $Id: map_object.c,v 1.2 1998/03/06 22:14:53 jdp Exp $
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*/
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#include <sys/param.h>
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#include <sys/mman.h>
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#include <assert.h>
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#include <errno.h>
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#include <stddef.h>
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#include <string.h>
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#include <unistd.h>
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#include "rtld.h"
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static int protflags(int); /* Elf flags -> mmap protection */
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/*
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* Map a shared object into memory. The argument is a file descriptor,
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* which must be open on the object and positioned at its beginning.
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*
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* The return value is a pointer to a newly-allocated Obj_Entry structure
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* for the shared object. Returns NULL on failure.
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*/
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Obj_Entry *
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map_object(int fd)
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{
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Obj_Entry *obj;
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union {
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Elf32_Ehdr hdr;
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char buf[PAGE_SIZE];
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} u;
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int nbytes;
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Elf32_Phdr *phdr;
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Elf32_Phdr *phlimit;
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Elf32_Phdr *segs[2];
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int nsegs;
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Elf32_Phdr *phdyn;
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Elf32_Phdr *phphdr;
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caddr_t mapbase;
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size_t mapsize;
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Elf32_Off base_offset;
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Elf32_Addr base_vaddr;
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Elf32_Addr base_vlimit;
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caddr_t base_addr;
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Elf32_Off data_offset;
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Elf32_Addr data_vaddr;
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Elf32_Addr data_vlimit;
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caddr_t data_addr;
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Elf32_Addr clear_vaddr;
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caddr_t clear_addr;
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size_t nclear;
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Elf32_Addr bss_vaddr;
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Elf32_Addr bss_vlimit;
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caddr_t bss_addr;
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if ((nbytes = read(fd, u.buf, PAGE_SIZE)) == -1) {
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_rtld_error("Read error: %s", strerror(errno));
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return NULL;
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}
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/* Make sure the file is valid */
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if (nbytes < sizeof(Elf32_Ehdr)
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|| u.hdr.e_ident[EI_MAG0] != ELFMAG0
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|| u.hdr.e_ident[EI_MAG1] != ELFMAG1
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|| u.hdr.e_ident[EI_MAG2] != ELFMAG2
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|| u.hdr.e_ident[EI_MAG3] != ELFMAG3) {
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_rtld_error("Invalid file format");
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return NULL;
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}
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if (u.hdr.e_ident[EI_CLASS] != ELFCLASS32
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|| u.hdr.e_ident[EI_DATA] != ELFDATA2LSB) {
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_rtld_error("Unsupported file layout");
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return NULL;
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}
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if (u.hdr.e_ident[EI_VERSION] != EV_CURRENT
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|| u.hdr.e_version != EV_CURRENT) {
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_rtld_error("Unsupported file version");
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return NULL;
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}
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if (u.hdr.e_type != ET_EXEC && u.hdr.e_type != ET_DYN) {
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_rtld_error("Unsupported file type");
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return NULL;
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}
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if (u.hdr.e_machine != EM_386) {
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_rtld_error("Unsupported machine");
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return NULL;
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}
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/*
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* We rely on the program header being in the first page. This is
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* not strictly required by the ABI specification, but it seems to
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* always true in practice. And, it simplifies things considerably.
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*/
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assert(u.hdr.e_phentsize == sizeof(Elf32_Phdr));
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assert(u.hdr.e_phoff + u.hdr.e_phnum*sizeof(Elf32_Phdr) <= PAGE_SIZE);
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assert(u.hdr.e_phoff + u.hdr.e_phnum*sizeof(Elf32_Phdr) <= nbytes);
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/*
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* Scan the program header entries, and save key information.
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*
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* We rely on there being exactly two load segments, text and data,
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* in that order.
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*/
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phdr = (Elf32_Phdr *) (u.buf + u.hdr.e_phoff);
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phlimit = phdr + u.hdr.e_phnum;
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nsegs = 0;
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phdyn = NULL;
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phphdr = NULL;
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while (phdr < phlimit) {
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switch (phdr->p_type) {
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case PT_LOAD:
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assert(nsegs < 2);
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segs[nsegs] = phdr;
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++nsegs;
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break;
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case PT_PHDR:
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phphdr = phdr;
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break;
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case PT_DYNAMIC:
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phdyn = phdr;
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break;
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}
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++phdr;
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}
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if (phdyn == NULL) {
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_rtld_error("Object is not dynamically-linked");
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return NULL;
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}
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assert(nsegs == 2);
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assert(segs[0]->p_align <= PAGE_SIZE);
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assert(segs[1]->p_align <= PAGE_SIZE);
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/*
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* Map the entire address space of the object, to stake out our
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* contiguous region, and to establish the base address for relocation.
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*/
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base_offset = trunc_page(segs[0]->p_offset);
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base_vaddr = trunc_page(segs[0]->p_vaddr);
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base_vlimit = round_page(segs[1]->p_vaddr + segs[1]->p_memsz);
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mapsize = base_vlimit - base_vaddr;
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base_addr = u.hdr.e_type == ET_EXEC ? (caddr_t) base_vaddr : NULL;
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mapbase = mmap(base_addr, mapsize, protflags(segs[0]->p_flags),
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MAP_PRIVATE, fd, base_offset);
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if (mapbase == (caddr_t) -1) {
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_rtld_error("mmap of entire address space failed: %s",
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strerror(errno));
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return NULL;
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}
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if (base_addr != NULL && mapbase != base_addr) {
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_rtld_error("mmap returned wrong address: wanted %p, got %p",
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base_addr, mapbase);
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munmap(mapbase, mapsize);
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return NULL;
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}
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/* Overlay the data segment onto the proper region. */
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data_offset = trunc_page(segs[1]->p_offset);
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data_vaddr = trunc_page(segs[1]->p_vaddr);
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data_vlimit = round_page(segs[1]->p_vaddr + segs[1]->p_filesz);
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data_addr = mapbase + (data_vaddr - base_vaddr);
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if (mmap(data_addr, data_vlimit - data_vaddr, protflags(segs[1]->p_flags),
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MAP_PRIVATE|MAP_FIXED, fd, data_offset) == (caddr_t) -1) {
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_rtld_error("mmap of data failed: %s", strerror(errno));
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return NULL;
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}
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/* Clear any BSS in the last page of the data segment. */
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clear_vaddr = segs[1]->p_vaddr + segs[1]->p_filesz;
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clear_addr = mapbase + (clear_vaddr - base_vaddr);
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if ((nclear = data_vlimit - clear_vaddr) > 0)
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memset(clear_addr, 0, nclear);
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/* Overlay the BSS segment onto the proper region. */
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bss_vaddr = data_vlimit;
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bss_vlimit = round_page(segs[1]->p_vaddr + segs[1]->p_memsz);
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bss_addr = mapbase + (bss_vaddr - base_vaddr);
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if (bss_vlimit > bss_vaddr) { /* There is something to do */
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if (mmap(bss_addr, bss_vlimit - bss_vaddr, protflags(segs[1]->p_flags),
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MAP_PRIVATE|MAP_FIXED|MAP_ANON, -1, 0) == (caddr_t) -1) {
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_rtld_error("mmap of bss failed: %s", strerror(errno));
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return NULL;
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}
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}
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obj = CNEW(Obj_Entry);
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obj->mapbase = mapbase;
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obj->mapsize = mapsize;
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obj->textsize = round_page(segs[0]->p_vaddr + segs[0]->p_memsz) -
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base_vaddr;
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obj->vaddrbase = base_vaddr;
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obj->relocbase = mapbase - base_vaddr;
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obj->dynamic = (const Elf32_Dyn *)
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(mapbase + (phdyn->p_vaddr - base_vaddr));
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if (u.hdr.e_entry != 0)
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obj->entry = (caddr_t) (mapbase + (u.hdr.e_entry - base_vaddr));
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if (phphdr != NULL) {
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obj->phdr = (const Elf32_Phdr *)
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(mapbase + (phphdr->p_vaddr - base_vaddr));
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obj->phsize = phphdr->p_memsz;
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}
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return obj;
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}
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/*
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* Given a set of ELF protection flags, return the corresponding protection
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* flags for MMAP.
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*/
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static int
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protflags(int elfflags)
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{
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int prot = 0;
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if (elfflags & PF_R)
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prot |= PROT_READ;
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if (elfflags & PF_W)
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prot |= PROT_WRITE;
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if (elfflags & PF_X)
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prot |= PROT_EXEC;
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return prot;
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}
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