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#!/usr/bin/env -S tcc -run
#include <elf.h>
#include <errno.h>
#include <fcntl.h>
#include <stdlib.h>
#include <stdio.h>
#include <string.h>
#include <sys/mman.h>
#include <unistd.h>
// ELF is defined assuming 8-bit bytes
#include <stdint.h>
int main64(int fd, char endianness);
int main(void)
{
int fd = open("./Library.so", O_RDONLY);
unsigned char e_ident[EI_NIDENT];
if (read(fd, e_ident, EI_NIDENT) != EI_NIDENT)
return 1;
if (e_ident[EI_MAG0] != ELFMAG0 || e_ident[EI_MAG1] != ELFMAG1
|| e_ident[EI_MAG2] != ELFMAG2 || e_ident[EI_MAG3] != ELFMAG3) {
puts("This doesn't seem to be an ELF file.");
return 1;
}
char endianness;
switch (e_ident[EI_DATA]) {
case ELFDATA2LSB:
endianness = 0;
break;
case ELFDATA2MSB:
endianness = 1;
break;
default:
puts("Your ELF file seems invalid.");
return 1;
}
switch (e_ident[EI_CLASS]) {
case ELFCLASS32:
puts("32-bit ELF loading not yet implemented.");
return 1;
case ELFCLASS64:
return main64(fd, endianness);
default:
puts("Your ELF file seems invalid.");
return 1;
}
return 2;
}
int main64(int fd, char endianness)
{
Elf64_Ehdr elf_header;
if (pread(fd, &elf_header, sizeof(elf_header), 0) != sizeof(elf_header))
return 1;
if (elf_header.e_type != ET_DYN) {
puts("This is not a shared library.");
return 1;
}
if (elf_header.e_version != EV_CURRENT) {
puts("Well... at the very least, the naming here is poor.");
return 1;
}
Elf64_Shdr *section_headers;
section_headers = calloc(sizeof(*section_headers), elf_header.e_shnum);
if (!section_headers && elf_header.e_shnum != 0) {
puts("OOM.");
return 1;
}
if (elf_header.e_shentsize != sizeof(*section_headers)) {
puts("Your ELF file seems wrong.");
return 1;
}
size_t shnum = elf_header.e_shnum;
for (size_t i = 0; i < shnum; i++) {
size_t remaining = elf_header.e_shentsize;
size_t got = 0;
ssize_t res;
do {
res =
pread(fd, &(section_headers[i]), remaining,
elf_header.e_shoff +
(elf_header.e_shentsize * i));
if (res < 0) {
puts("Failed to read ELF section headers");
return 1;
}
got += res;
remaining -= res;
} while (remaining != 0);
}
Elf64_Phdr *program_headers;
program_headers = calloc(sizeof(*program_headers), elf_header.e_phnum);
if (!program_headers && elf_header.e_phnum != 0) {
puts("OOM.");
return 1;
}
if (elf_header.e_phentsize != sizeof(*program_headers)) {
puts("Your ELF file seems wrong.");
return 1;
}
size_t phnum = elf_header.e_phnum;
if (phnum >= PN_XNUM) {
if (shnum == 0) {
puts("Your ELF file is broken.");
return 1;
}
}
for (size_t i = 0; i < phnum; i++) {
size_t remaining = elf_header.e_phentsize;
size_t got = 0;
ssize_t res;
do {
res =
pread(fd, &(program_headers[i]), remaining,
elf_header.e_phoff +
(elf_header.e_phentsize * i));
if (res < 0) {
puts("Failed to read ELF section headers");
return 1;
}
got += res;
remaining -= res;
} while (remaining != 0);
printf("loaded phent at %lu\n",
elf_header.e_phoff + (elf_header.e_phentsize * i));
}
unsigned char **loaded_segments;
loaded_segments = malloc(phnum * sizeof(*loaded_segments));
for (size_t i = 0; i < phnum; i++) {
int prot = 0;
switch (program_headers[i].p_type) {
case PT_LOAD:
// size_t;
size_t pre_padding;
if (program_headers[i].p_align == 0)
pre_padding = 0;
else
pre_padding =
program_headers[i].p_offset %
program_headers[i].p_align;
loaded_segments[i] =
mmap(0, pre_padding + program_headers[i].p_memsz,
PROT_WRITE, MAP_PRIVATE | MAP_ANONYMOUS, -1,
0);
if (!loaded_segments[i]) {
puts("OOM!");
return 1;
}
printf("Mapped new segment of %lu length at %p\n",
pre_padding + program_headers[i].p_memsz,
loaded_segments[i]);
size_t offset = 0;
size_t remaining = program_headers[i].p_filesz;
do {
ssize_t res = pread(fd,
&(loaded_segments[i]
[offset + pre_padding]),
remaining,
program_headers[i].p_offset
+ offset);
if (res < 0) {
puts("pread failed");
printf("errno: %d\n", errno);
return 1;
}
offset += res;
remaining -= res;
} while (remaining != 0);
break;
case PT_DYNAMIC:
break;
default:
break;
}
}
return 0;
}
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