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4282 - subx now loads teensy/test4 

We're now parsing the ELF spec more closely and better handling multiple
program header table entries.
This commit is contained in:
Kartik Agaram 2018-06-28 15:22:13 -07:00
parent bbe7cd53cb
commit 96b2216bf8
1 changed files with 53 additions and 13 deletions
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66
subx/020elf.cc
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@ -27,23 +27,32 @@ void load_elf(const string& filename) {
void load_elf_contents(uint8_t* elf_contents, size_t size) {
uint8_t magic[5] = {0};
memcpy(magic, elf_contents, 4);
if (0 != memcmp(magic, "\177ELF", 4))
if (memcmp(magic, "\177ELF", 4) != 0)
die("Invalid ELF file starting with \"%s\"", magic);
uint32_t e_type = u32_in(&elf_contents[16]);
if (0x00030002 != e_type)
die("ELF type/machine 0x%x isn't i386 executable", e_type);
if (elf_contents[4] != 1)
die("Only 32-bit ELF files (4-byte words; virtual addresses up to 4GB) supported.\n");
if (elf_contents[5] != 1)
die("Only little-endian ELF files supported.\n");
// unused: remaining 10 bytes of e_ident
uint32_t e_machine_type = u32_in(&elf_contents[16]);
if (e_machine_type != 0x00030002)
die("ELF type/machine 0x%x isn't i386 executable", e_machine_type);
// unused: e_version. We only support version 1, and later versions will be backwards compatible.
uint32_t e_entry = u32_in(&elf_contents[24]);
uint32_t e_phoff = u32_in(&elf_contents[28]);
uint32_t p_vaddr = u32_in(&elf_contents[e_phoff + 8]);
uint32_t p_memsz = u32_in(&elf_contents[e_phoff + 20]);
// unused: e_shoff
// unused: e_flags
uint32_t e_ehsize = u16_in(&elf_contents[40]);
if (e_ehsize < 52) die("Invalid binary; ELF header too small\n");
uint32_t e_phentsize = u16_in(&elf_contents[42]);
uint32_t e_phnum = u16_in(&elf_contents[44]);
cerr << e_phnum << " entries in the program header, each " << e_phentsize << " bytes long\n";
// unused: e_shentsize
// unused: e_shnum
// unused: e_shstrndx
Mem.resize(p_vaddr + p_memsz);
if (size > p_memsz - p_vaddr) size = p_memsz - p_vaddr;
for (size_t i = 0; i < size; ++i)
Mem.at(p_vaddr + i) = elf_contents[i];
End_of_program = p_vaddr + p_memsz;
for (size_t i = 0; i < e_phnum; ++i)
load_program_header(elf_contents, size, e_phoff + i*e_phentsize, e_ehsize);
// TODO: need to set up real stack somewhere
@ -51,10 +60,41 @@ void load_elf_contents(uint8_t* elf_contents, size_t size) {
EIP = e_entry;
}
void load_program_header(uint8_t* elf_contents, size_t size, uint32_t offset, uint32_t e_ehsize) {
uint32_t p_type = u32_in(&elf_contents[offset]);
cerr << "program header at offset " << offset << ": type " << p_type << '\n';
if (p_type != 1) {
cerr << "ignoring segment at offset " << offset << " of non PT_LOAD type " << p_type << " (see http://refspecs.linuxbase.org/elf/elf.pdf)\n";
return;
}
uint32_t p_offset = u32_in(&elf_contents[offset + 4]);
uint32_t p_vaddr = u32_in(&elf_contents[offset + 8]);
if (e_ehsize > p_vaddr) die("Invalid binary; program header overlaps ELF header\n");
// unused: p_paddr
uint32_t p_filesz = u32_in(&elf_contents[offset + 16]);
uint32_t p_memsz = u32_in(&elf_contents[offset + 20]);
if (p_filesz != p_memsz)
die("Can't handle segments where p_filesz != p_memsz (see http://refspecs.linuxbase.org/elf/elf.pdf)\n");
if (p_offset + p_filesz > size)
die("Invalid binary; segment at offset %d is too large: wants to end at %d but the file ends at %d\n", offset, p_offset+p_filesz, size);
Mem.resize(p_vaddr + p_memsz);
if (size > p_memsz) size = p_memsz;
cerr << "blitting file offsets (" << p_offset << ", " << (p_offset+p_filesz) << ") to addresses (" << p_vaddr << ", " << (p_vaddr+p_memsz) << ")\n";
for (size_t i = 0; i < p_filesz; ++i)
Mem.at(p_vaddr + i) = elf_contents[p_offset + i];
if (End_of_program < p_vaddr+p_memsz)
End_of_program = p_vaddr+p_memsz;
}
inline uint32_t u32_in(uint8_t* p) {
return p[0] | p[1] << 8 | p[2] << 16 | p[3] << 24;
}
inline uint16_t u16_in(uint8_t* p) {
return p[0] | p[1] << 8;
}
void die(const char* format, ...) {
va_list args;
va_start(args, format);