feat: add gen_reloc script for ELF relocation processing

1 files changed, 224 insertions, 0 deletions

diff --git a/na/scripts/gen_reloc.py b/na/scripts/gen_reloc.py
new file mode 100644
index 0000000..6709e17
--- /dev/null
+++ b/na/scripts/gen_reloc.py
@@ -0,0 +1,224 @@
+#!/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)