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drasko |
/*
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* ELF manipulation routines
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*
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* Copyright (C) 2008 Bahadir Balban
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*/
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#include <memory.h>
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#include <vm_area.h>
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#include <l4/api/errno.h>
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#include <lib/elf/elf.h>
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#include <lib/elf/elfprg.h>
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#include <lib/elf/elfsym.h>
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#include <lib/elf/elfsect.h>
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int elf_probe(struct elf_header *header)
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{
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/* Test that it is a 32-bit little-endian ELF file */
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if (header->e_ident[EI_MAG0] == ELFMAG0 &&
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header->e_ident[EI_MAG1] == ELFMAG1 &&
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header->e_ident[EI_MAG2] == ELFMAG2 &&
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header->e_ident[EI_MAG3] == ELFMAG3 &&
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header->e_ident[EI_CLASS] == ELFCLASS32 &&
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header->e_ident[EI_DATA] == ELFDATA2LSB)
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return 0;
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else
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return -1;
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}
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/*
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* Sets or expands a segment region if it has the given type and flags
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* For expansion we assume any new section must come consecutively
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* after the existing segment, otherwise we ignore it for simplicity.
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*/
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int elf_test_expand_segment(struct elf_section_header *section,
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unsigned int sec_type, unsigned int sec_flags,
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unsigned int sec_flmask, unsigned long *start,
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unsigned long *end, unsigned long *offset)
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{
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if (section->sh_type == sec_type &&
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(section->sh_flags & sec_flmask) == sec_flags) {
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/* Set new section */
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if (!*start) {
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BUG_ON(*offset || *end);
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*offset = section->sh_offset;
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*start = section->sh_addr;
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*end = section->sh_addr + section->sh_size;
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/* Expand existing section from the end */
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} else if (*end == section->sh_addr)
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*end = section->sh_addr + section->sh_size;
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}
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return 0;
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}
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/*
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* Sift through sections and copy their marks to tcb and efd
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* if they are recognised and loadable sections. Test the
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* assigned segment marks and return an error if they're invalid.
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*/
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int elf_mark_segments(struct elf_section_header *sect_header, int nsections,
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struct tcb *task, struct exec_file_desc *efd)
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{
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for (int i = 0; i < nsections; i++) {
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struct elf_section_header *section = §_header[i];
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/* Text + read-only data segments */
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elf_test_expand_segment(section, SHT_PROGBITS,
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SHF_ALLOC, SHF_ALLOC | SHF_WRITE,
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&task->text_start, &task->text_end,
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&efd->text_offset);
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/* Data segment */
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elf_test_expand_segment(section, SHT_PROGBITS, SHF_ALLOC |
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SHF_WRITE, SHF_ALLOC | SHF_WRITE,
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&task->data_start, &task->data_end,
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&efd->data_offset);
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/* Bss segment */
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elf_test_expand_segment(section, SHT_NOBITS, SHF_ALLOC |
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SHF_WRITE, SHF_ALLOC | SHF_WRITE,
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&task->bss_start, &task->bss_end,
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&efd->bss_offset);
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}
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/* Test anomalies with the mappings */
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/* No text */
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if (!task->text_start) {
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printf("%s: Error: Could not find a text "
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"segment in ELF file.\n", __FUNCTION__);
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return -ENOEXEC;
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}
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/* Warn if no data or bss but it's not an error */
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if (!task->data_start || !task->bss_start) {
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printf("%s: NOTE: Could not find a data and/or "
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"bss segment in ELF file.\n", __FUNCTION__);
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}
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/* Data and text are on the same page and not on a page boundary */
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if (!((is_page_aligned(task->data_start) &&
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task->data_start == task->text_end) ||
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(page_align(task->data_start) > page_align(task->text_end))))
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if ((task->data_start - task->text_end) < PAGE_SIZE &&
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!is_page_aligned(task->text_end)) {
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printf("%s: Error: Distance between data and text"
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" sections are less than page size (%d bytes)\n",
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__FUNCTION__, PAGE_SIZE);
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return -ENOEXEC;
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}
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return 0;
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}
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/*
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* Loading an ELF file:
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*
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* This first probes and detects that the given file is a valid elf file.
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* Then it looks at the program header table to find the first (probably
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* only) segment that has type LOAD. Then it looks at the section header
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* table, to find out about every loadable section that is part of this
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* aforementioned loadable program segment. Each section is marked in the
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* efd and tcb structures for further memory mappings.
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*/
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int elf_parse_executable(struct tcb *task, struct vm_file *file,
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struct exec_file_desc *efd)
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{
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struct elf_header elf_header, *elf_headerp = pager_map_page(file, 0);
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struct elf_program_header *prg_header_start, *prg_header_load;
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struct elf_section_header *sect_header;
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unsigned long sect_offset, sect_size;
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unsigned long prg_offset, prg_size;
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int err = 0;
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/* Test that it is a valid elf file */
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if ((err = elf_probe(elf_headerp)) < 0)
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return err;
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/* Copy the elf header and unmap first page */
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memcpy(&elf_header, elf_headerp, sizeof(elf_header));
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pager_unmap_page(elf_headerp);
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/* Find the markers for section and program header tables */
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sect_offset = elf_header.e_shoff;
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sect_size = elf_header.e_shentsize * elf_header.e_shnum;
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prg_offset = elf_header.e_phoff;
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prg_size = elf_header.e_phentsize * elf_header.e_phnum;
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/* Get the program header table */
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prg_header_start = (struct elf_program_header *)
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pager_map_file_range(file, prg_offset, prg_size);
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/* Get the first loadable segment. We currently just stare at it */
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for (int i = 0; i < elf_header.e_phnum; i++) {
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if (prg_header_start[i].p_type == PT_LOAD) {
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prg_header_load = &prg_header_start[i];
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break;
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}
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}
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/* Get the section header table */
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sect_header = (struct elf_section_header *)
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pager_map_file_range(file, sect_offset, sect_size);
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/* Copy segment marks from ELF file to task + efd. Return errors */
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err = elf_mark_segments(sect_header, elf_header.e_shnum, task, efd);
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/* Unmap program header table */
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pager_unmap_pages(prg_header_start, __pfn(page_align_up(prg_size)));
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/* Unmap section header table */
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pager_unmap_pages(sect_header, __pfn(page_align_up(sect_size)));
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return err;
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}
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