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/*
* ELF loader.
* Copyright (C) 2023, @stsp
*
* This program is free software: you can redistribute it and/or modify
* it under the terms of the GNU General Public License as published by
* the Free Software Foundation, either version 3 of the License, or
* (at your option) any later version.
*
* This program is distributed in the hope that it will be useful,
* but WITHOUT ANY WARRANTY; without even the implied warranty of
* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
* GNU General Public License for more details.
*
* You should have received a copy of the GNU General Public License
* along with this program. If not, see <https://www.gnu.org/licenses/>.
*
*/
#include <stdio.h>
#include <stdlib.h>
#include <stdint.h>
#include <string.h>
#include <unistd.h>
#include <assert.h>
#include "util.h"
#include "stub.h"
#include "elf.h"
#include "elfp.h"
#define STUB_DEBUG 0
#if STUB_DEBUG
#define stub_debug(...) printf(__VA_ARGS__)
#else
#define stub_debug(...)
#endif
struct elf_h {
uint32_t va;
uint32_t length;
uint32_t entry;
int phnum;
Elf32_Phdr phdr[0];
};
static void *read_elf_headers(int ifile)
{
Elf32_Ehdr ehdr;
struct elf_h *h;
int i, rc;
long beg = 0, end = 0;
rc = read(ifile, &ehdr, sizeof(ehdr)); /* get the ELF header */
if (rc != sizeof(ehdr)) {
fprintf(stderr, "cant read ELF header\n");
return NULL;
}
if (memcmp(&ehdr.e_ident, ELFMAG, SELFMAG) ||
ehdr.e_ehsize != sizeof(ehdr) ||
ehdr.e_phentsize != sizeof(Elf32_Phdr)) {
fprintf(stderr, "bad ELF header\n");
return NULL;
}
if (ehdr.e_ident[EI_CLASS] != ELFCLASS32) {
fprintf(stderr, "bad ELF class %i\n", ehdr.e_ident[EI_CLASS]);
return NULL;
}
if (ehdr.e_phoff > sizeof(ehdr))
lseek(ifile, ehdr.e_phoff - sizeof(ehdr), SEEK_CUR);
h = malloc(sizeof(*h) + sizeof(Elf32_Phdr) * ehdr.e_phnum);
assert(h);
rc = read(ifile, h->phdr, sizeof(Elf32_Phdr) * ehdr.e_phnum);
if (rc != sizeof(Elf32_Phdr) * ehdr.e_phnum) {
fprintf(stderr, "can't read phdr\n");
return NULL;
}
h->phnum = ehdr.e_phnum;
for (i = 0; i < ehdr.e_phnum; i++) {
Elf32_Phdr *phdr = &h->phdr[i];
if (phdr->p_type != PT_LOAD)
continue;
if (phdr->p_align != 4096) {
fprintf(stderr, "unsupported ELF alignment %li\n", phdr->p_align);
return NULL;
}
if (phdr->p_vaddr < beg || !beg)
beg = phdr->p_vaddr;
if (phdr->p_vaddr + phdr->p_memsz > end)
end = phdr->p_vaddr + phdr->p_memsz;
#if STUB_DEBUG
stub_debug("PHDR pa 0x%lx va 0x%lx size 0x%lx foffs 0x%lx\n",
phdr->p_paddr, phdr->p_vaddr, phdr->p_filesz, phdr->p_offset);
#endif
}
h->entry = ehdr.e_entry;
h->va = beg;
h->length = end - beg;
return h;
}
static uint32_t get_elf_length(void *handle)
{
struct elf_h *h = handle;
return h->length;
}
static uint32_t get_elf_entry(void *handle)
{
struct elf_h *h = handle;
return h->entry;
}
static uint32_t get_elf_va(void *handle)
{
struct elf_h *h = handle;
return h->va;
}
static void read_elf_sections(void *handle, char __far *ptr, int ifile,
uint32_t offset)
{
struct elf_h *h = handle;
int i;
for (i = 0; i < h->phnum; i++) {
Elf32_Phdr *phdr = &h->phdr[i];
long bytes;
if (phdr->p_type != PT_LOAD)
continue;
lseek(ifile, offset + phdr->p_offset, SEEK_SET);
bytes = _long_read(ifile, ptr, phdr->p_vaddr, phdr->p_filesz);
stub_debug("read returned %li\n", bytes);
if (bytes != phdr->p_filesz) {
fprintf(stderr, "err reading %li bytes, got %li\n",
phdr->p_filesz, bytes);
_exit(EXIT_FAILURE);
}
if (phdr->p_memsz > phdr->p_filesz) {
uint32_t len = phdr->p_memsz - phdr->p_filesz;
len += len & 1; // word-align
farmemset(ptr, phdr->p_vaddr + phdr->p_filesz, 0, len);
}
}
free(h);
}
struct ldops elf_ops = {
read_elf_headers,
get_elf_va,
get_elf_length,
get_elf_entry,
read_elf_sections,
};
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