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#include <merror.h>
#include <elf.h>
#include <melf.h>
#include <stdint.h>
#include <stdio.h>
#include <stdlib.h>
#include <sys/mman.h>
#include "sim.h"
#define SEC_ALIGN 0x1000
#define PAGE_SIZE 4096
#define BITFILED_LEN (UINT32_MAX / PAGE_SIZE / 8)
struct load_state {
FILE *file;
int fd;
uint32_t file_sz;
Elf32_Phdr *phdr;
uint32_t phdr_len;
Elf32_Ehdr ehdr;
};
static int assert_ehdr(const void *const given, const void *const assert,
size_t size)
{
if (memcmp(given, assert, size) == 0)
return M_SUCCESS;
ERROR("invalid elf ehdr");
return M_ERROR;
}
static int load_ehdr(struct simulator *sim, struct load_state *state)
{
Elf32_Ehdr ehdr;
fseek(state->file, 0, SEEK_SET);
if (fread(&ehdr, sizeof(Elf32_Ehdr), 1, state->file) != 1) {
ERROR("cannot load ehdr");
return M_ERROR;
}
/**
* Compare each "static" value in the ehdr and make sure it
* is what it should be. If not throw and error and eventually
* return.
*/
Elf32_Ehdr baseline = MIPS_ELF_EHDR;
baseline.e_type = B16(ET_EXEC);
#define EHDR_ASSERT(name, size) \
if (res == M_SUCCESS) \
res |= assert_ehdr(&baseline.e_##name, \
&ehdr.e_##name, size) \
// ignore abi ver
ehdr.e_ident[EI_ABIVERSION] = 0x00;
int res = 0;
EHDR_ASSERT(ident, EI_NIDENT);
EHDR_ASSERT(type, sizeof(Elf32_Half));
EHDR_ASSERT(machine, sizeof(Elf32_Half));
EHDR_ASSERT(version, sizeof(Elf32_Word));
// EHDR_ASSERT(flags, sizeof(Elf32_Word));
EHDR_ASSERT(ehsize, sizeof(Elf32_Half));
EHDR_ASSERT(phentsize, sizeof(Elf32_Half));
EHDR_ASSERT(shentsize, sizeof(Elf32_Half));
#undef EHDR_ASSERT
if (res)
return M_ERROR;
state->ehdr = ehdr;
sim->entry = B32(ehdr.e_entry);
return M_SUCCESS;
}
static int load_phdr(struct load_state *state)
{
Elf32_Phdr *phdr = NULL;
uint32_t off = B32(state->ehdr.e_phoff);
uint16_t len = B16(state->ehdr.e_phnum);
if (BOUND_CHK(state->file_sz, len, off)) {
ERROR("elf phdr location invalid");
return M_ERROR;
}
phdr = malloc(sizeof(Elf32_Phdr) * len);
if (phdr == NULL) {
PERROR("cannot alloc");
return M_ERROR;
}
fseek(state->file, off, SEEK_SET);
if (fread(phdr, sizeof(Elf32_Phdr), len, state->file) != len) {
free(phdr);
PERROR("cannot read phdr");
return M_ERROR;
}
state->phdr = phdr;
state->phdr_len = len;
return M_SUCCESS;
}
static void set_page(uint8_t *bitfield, uint32_t addr)
{
int idx = (addr / PAGE_SIZE) / 8;
int off = (addr / PAGE_SIZE) % 8;
bitfield[idx] |= 1 << off;
}
static int get_page(const uint8_t *const bitfield, uint32_t addr)
{
int idx = (addr / PAGE_SIZE) / 8;
int off = (addr / PAGE_SIZE) % 8;
return ((bitfield[idx] >> off) & 1);
}
static int load_segment(struct simulator *sim, struct load_state *state,
Elf32_Phdr *hdr, uint8_t* bitfield)
{
uint32_t addr = B32(hdr->p_vaddr),
off = B32(hdr->p_offset),
len = B32(hdr->p_filesz),
flags = B32(hdr->p_flags);
bool exec = flags & PF_X;
// ignore if empty
if (len < 1)
return M_SUCCESS;
// make sure segment is acutally inside
// the file
if (BOUND_CHK(state->file_sz, len, off)) {
ERROR("segment location invalid");
return M_ERROR;
}
// make sure the vitural address is also
// valid
if (BOUND_CHK(UINT32_MAX, len, addr)) {
ERROR("segment vitural addr invalid");
return M_ERROR;
}
// update text seg bounds
if (exec) {
if (addr < sim->text_min)
sim->text_min = addr;
if (addr + len > sim->text_max)
sim->text_max = addr + len;
}
// align the mapping ptr to
// the page size
uintptr_t ptr = (addr / PAGE_SIZE) * PAGE_SIZE;
// map each page that the segment
// requires
for (; ptr < addr + len; ptr += PAGE_SIZE) {
// dont remap if address is
// already mapped
if (get_page(bitfield, ptr))
continue;
// set page as mapped
set_page(bitfield, ptr);
void *res = mmap(
(void *) ptr, PAGE_SIZE,
PROT_READ | PROT_WRITE,
MAP_PRIVATE | MAP_FIXED | MAP_ANONYMOUS, -1, 0);
if ((uintptr_t) res != ptr) {
PERROR("failed to map executable");
return M_ERROR;
}
}
// load the segment into the mapped memory
fseek(state->file, off, SEEK_SET);
fread((void *) (uintptr_t) addr, 1, len, state->file);
return M_SUCCESS;
}
static int load_memory(struct simulator *sim, struct load_state *state)
{
// map each page in a 32bit address space to a single bit
// in the bitfield
uint8_t *bitfield = malloc(BITFILED_LEN);
if (bitfield == NULL) {
PERROR("cannot alloc");
return M_ERROR;
}
memset(bitfield, 0, BITFILED_LEN);
for (uint32_t i = 0; i < state->phdr_len; i++) {
Elf32_Phdr *hdr = &state->phdr[i];
if (load_segment(sim, state, hdr, bitfield))
return M_ERROR;
}
free(bitfield);
return M_SUCCESS;
}
int sim_load_file(struct simulator *sim) {
struct load_state state;
state.file = fopen(sim->args->executable, "r");
if (state.file == NULL) {
PERROR("cannot read '%s'", state.file);
return M_ERROR;
}
state.fd = fileno(state.file);
// get filesize
fseek(state.file, 0, SEEK_END);
state.file_sz = ftell(state.file);
state.phdr = NULL;
int res = M_SUCCESS;
if (res == M_SUCCESS)
res = load_ehdr(sim, &state);
if (res == M_SUCCESS)
res = load_phdr(&state);
if (res == M_SUCCESS)
res = load_memory(sim, &state);
if (state.phdr)
free(state.phdr);
fclose(state.file);
return res;
}
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