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#!/usr/bin/env python3
# SPDX-License-Identifier: GPL-2.0-or-later
# Copyright (C) 2026 Richard Qin
import argparse
import struct
import sys
ELF_MAGIC = b"\x7fELF"
ELFCLASS64 = 2
ELFDATA2LSB = 1
EM_RISCV = 243
SHT_SYMTAB = 2
SHT_RELA = 4
PT_LOAD = 1
R_RISCV_64 = 2
R_RISCV_RELATIVE = 3
RELOC_MAGIC = 0x4C554D45524C4F43 # "LUMERLOC"
RELOC_VERSION = 1
RELOC_ARCH_RISCV = 1
def read_struct(fmt, data, offset):
size = struct.calcsize(fmt)
return struct.unpack_from(fmt, data, offset), size
def parse_elf_header(data):
if data[:4] != ELF_MAGIC:
raise ValueError("not an ELF file")
ei_class = data[4]
ei_data = data[5]
if ei_class != ELFCLASS64 or ei_data != ELFDATA2LSB:
raise ValueError("unsupported ELF class/data")
fmt = "<16sHHIQQQIHHHHHH"
(e_ident, e_type, e_machine, e_version, e_entry, e_phoff, e_shoff,
e_flags, e_ehsize, e_phentsize, e_phnum, e_shentsize, e_shnum,
e_shstrndx), _ = read_struct(fmt, data, 0)
return {
"e_machine": e_machine,
"e_phoff": e_phoff,
"e_phentsize": e_phentsize,
"e_phnum": e_phnum,
"e_shoff": e_shoff,
"e_shentsize": e_shentsize,
"e_shnum": e_shnum,
"e_shstrndx": e_shstrndx,
}
def parse_program_headers(data, ehdr):
phdrs = []
fmt = "<IIQQQQQQ"
for i in range(ehdr["e_phnum"]):
off = ehdr["e_phoff"] + i * ehdr["e_phentsize"]
(p_type, p_flags, p_offset, p_vaddr, p_paddr, p_filesz, p_memsz,
p_align), _ = read_struct(fmt, data, off)
phdrs.append({
"p_type": p_type,
"p_offset": p_offset,
"p_vaddr": p_vaddr,
"p_filesz": p_filesz,
"p_memsz": p_memsz,
})
return phdrs
def parse_section_headers(data, ehdr):
shdrs = []
fmt = "<IIQQQQIIQQ"
for i in range(ehdr["e_shnum"]):
off = ehdr["e_shoff"] + i * ehdr["e_shentsize"]
(sh_name, sh_type, sh_flags, sh_addr, sh_offset, sh_size,
sh_link, sh_info, sh_addralign, sh_entsize), _ = read_struct(fmt, data, off)
shdrs.append({
"sh_name": sh_name,
"sh_type": sh_type,
"sh_addr": sh_addr,
"sh_offset": sh_offset,
"sh_size": sh_size,
"sh_link": sh_link,
"sh_entsize": sh_entsize,
})
return shdrs
def get_strtab(data, shdrs, idx):
sh = shdrs[idx]
return data[sh["sh_offset"]:sh["sh_offset"] + sh["sh_size"]]
def get_section_name(strtab, sh_name):
end = strtab.find(b"\x00", sh_name)
if end < 0:
return ""
return strtab[sh_name:end].decode("ascii", errors="ignore")
def find_symbol(data, shdrs, name):
for i, sh in enumerate(shdrs):
if sh["sh_type"] != SHT_SYMTAB:
continue
strtab = get_strtab(data, shdrs, sh["sh_link"])
entsize = sh["sh_entsize"] or 24
count = sh["sh_size"] // entsize
for j in range(count):
off = sh["sh_offset"] + j * entsize
(st_name, st_info, st_other, st_shndx, st_value, st_size), _ = read_struct(
"<IBBHQQ", data, off
)
sym_name = get_section_name(strtab, st_name)
if sym_name == name:
return st_value
return None
def read_symtab(data, shdrs, idx):
sh = shdrs[idx]
entsize = sh["sh_entsize"] or 24
count = sh["sh_size"] // entsize
syms = []
for j in range(count):
off = sh["sh_offset"] + j * entsize
(st_name, st_info, st_other, st_shndx, st_value, st_size), _ = read_struct(
"<IBBHQQ", data, off
)
syms.append((st_value, st_size, st_info, st_shndx))
return syms
def vaddr_in_load(vaddr, phdrs, size):
for ph in phdrs:
if ph["p_type"] != PT_LOAD:
continue
start = ph["p_vaddr"]
end = ph["p_vaddr"] + ph["p_memsz"]
if vaddr >= start and vaddr + size <= end:
return True
return False
def main():
ap = argparse.ArgumentParser()
ap.add_argument("--elf", required=True)
ap.add_argument("--out", required=True)
args = ap.parse_args()
data = open(args.elf, "rb").read()
ehdr = parse_elf_header(data)
if ehdr["e_machine"] != EM_RISCV:
raise ValueError("only EM_RISCV supported")
phdrs = parse_program_headers(data, ehdr)
shdrs = parse_section_headers(data, ehdr)
link_base = find_symbol(data, shdrs, "_start")
if link_base is None:
raise ValueError("_start symbol not found")
image_end = find_symbol(data, shdrs, "__lume_image_end")
if image_end is None:
raise ValueError("__lume_image_end symbol not found")
image_size = image_end - link_base
entries = []
for sh in shdrs:
if sh["sh_type"] != SHT_RELA:
continue
if sh["sh_link"] >= len(shdrs):
continue
symtab = read_symtab(data, shdrs, sh["sh_link"])
entsize = sh["sh_entsize"] or 24
count = sh["sh_size"] // entsize
for i in range(count):
off = sh["sh_offset"] + i * entsize
(r_offset, r_info, r_addend), _ = read_struct("<QQq", data, off)
r_type = r_info & 0xFFFFFFFF
r_sym = r_info >> 32
if r_type not in (R_RISCV_RELATIVE, R_RISCV_64):
continue
if r_offset < link_base or r_offset >= link_base + image_size:
continue
if not vaddr_in_load(r_offset, phdrs, 8):
continue
ent_offset = r_offset - link_base
if r_type == R_RISCV_RELATIVE:
ent_addend = r_addend
ent_type = 1
else:
sym_val = 0
if r_sym < len(symtab):
sym_val = symtab[r_sym][0]
ent_addend = sym_val + r_addend
if ent_addend < link_base or ent_addend >= link_base + image_size:
continue
ent_type = 2
entries.append((ent_offset, ent_addend, ent_type))
header = struct.pack(
"<QHHIII",
RELOC_MAGIC,
RELOC_VERSION,
RELOC_ARCH_RISCV,
24,
len(entries),
0,
)
with open(args.out, "wb") as f:
f.write(header)
for off, add, typ in entries:
f.write(struct.pack("<QQII", off, add, typ, 0))
return 0
if __name__ == "__main__":
try:
sys.exit(main())
except Exception as e:
print("gen_reloc: " + str(e), file=sys.stderr)
sys.exit(1)
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