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https://github.com/Mathewnd/Astral.git
synced 2026-10-27 12:48:22 +00:00
kernel: generate symbol tables
In preparation for printing file+function names in backtraces, add support for generating and linking three tables into the kernel: - dbg_sym_table: a table consisting of <uint32_t addr_offset, uint32_t function_name_offset, uint32_t file_name_offset>, being ordered by offset. - dbg_fn_name_table: a table consisting of packed NULL terminated strings, which the dbg_sym_table points into. - dbg_file_name_table: a table consisting of packed NULL terminated strings, which the dbg_sym_table points into.
This commit is contained in:
Matheus
@@ -68,6 +68,25 @@ SECTIONS
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*(.bss .bss.*)
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} :data
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. = ALIGN(4);
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.dbg_sym_table : {
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dbg_sym_table = .;
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KEEP(*(.dbg_sym_table));
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dbg_sym_table_end = .;
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} :data
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.dbg_fn_name_table : {
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dbg_fn_name_table = .;
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KEEP(*(.dbg_fn_name_table));
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dbg_fn_name_table_end = .;
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} :data
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.dbg_file_name_table : {
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dbg_file_name_table = .;
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KEEP(*(.dbg_file_name_table));
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dbg_file_name_table_end = .;
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} :data
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. = ALIGN(4K);
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_data_end = .;
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}
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Executable
+190
@@ -0,0 +1,190 @@
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#!/usr/bin/env python3
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# USAGE:
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# python3 gen_fn_sym.py kernel_exec base_addr source_cwd output_file
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#
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# - output_file is an ELF object exporting dbg_sym_table, dbg_fn_name_table,
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# dbg_file_name_table, and their corresponding _end symbols.
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# - Each symbol record is <uint32_t address, uint32_t function_name_offset,
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# uint32_t file_name_offset>. Addresses are relative to base_addr and string
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# offsets are byte offsets into the corresponding string table.
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# - Select matching tools with --nm, --objdump and --objcopy (or NM,
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# OBJDUMP and OBJCOPY envs).
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import argparse
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import os
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from pathlib import Path
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import shlex
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import struct
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import subprocess
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import tempfile
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from typing import NamedTuple
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UINT32_MAX = (1 << 32) - 1
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SECTION_MARKERS = {"_text_start", "_text_end"}
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class BfdTarget(NamedTuple):
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file_format: str
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architecture: str
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def run_tool(command):
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return subprocess.run(
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command, check=True, capture_output=True,
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encoding="utf-8", errors="surrogateescape",
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env={**os.environ, "LC_ALL": "C"},
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).stdout
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def tool_command(value):
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command = shlex.split(value)
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if not command:
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raise argparse.ArgumentTypeError("tool command must not be empty")
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return command
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def get_bfd_target(kernel_exec, objdump):
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output = run_tool([*objdump, "-f", "--", kernel_exec])
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file_format = architecture = None
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for line in output.splitlines():
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if "file format " in line:
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file_format = line.rsplit("file format ", 1)[1].strip()
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if line.startswith("architecture: "):
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architecture = line[len("architecture: "):].split(",", 1)[0].strip()
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if not file_format or not architecture or architecture == "UNKNOWN!":
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raise ValueError("objdump could not identify the kernel target; select a matching --objdump")
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return BfdTarget(file_format, architecture)
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def source_filename(location, source_prefix):
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if not location:
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return ""
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path, separator, line_number = location.rpartition(":")
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filename = path if separator and line_number.isdigit() else location
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filename = os.path.normpath(filename)
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if filename.startswith(source_prefix):
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filename = filename[len(source_prefix):]
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return filename
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def collect_symbols(kernel_exec, base_addr, source_cwd, nm):
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output = run_tool(
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[*nm, "-n", "-l", "--defined-only", "--format=bsd",
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"--no-demangle", "--radix=x", "--", kernel_exec],
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)
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source_prefix = os.path.abspath(source_cwd).rstrip(os.sep) + os.sep
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symbols = []
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for line in output.splitlines():
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symbol_text, _, location = line.partition("\t")
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fields = symbol_text.split(None, 2)
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if len(fields) != 3 or fields[1] not in ("T", "t"):
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continue
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address, _, name = fields
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if name in SECTION_MARKERS:
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continue
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offset = int(address, 16) - base_addr
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if not 0 <= offset <= UINT32_MAX:
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raise ValueError(f"address of {name} does not fit in uint32_t relative to base_addr")
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filename = source_filename(location, source_prefix)
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symbols.append((offset, name, filename))
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if not symbols:
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raise ValueError("kernel binary contains no text symbols")
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return sorted(symbols, key=lambda symbol: (symbol[0], symbol[1]))
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def intern_string(value, table, offsets):
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if value not in offsets:
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encoded = value.encode("utf-8", errors="surrogateescape") + b"\0"
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if len(table) + len(encoded) - 1 > UINT32_MAX:
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raise ValueError("string table does not fit in uint32_t offsets")
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offsets[value] = len(table)
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table.extend(encoded)
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return offsets[value]
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def make_tables(symbols):
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records = bytearray()
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functions = bytearray(b"\0")
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files = bytearray(b"\0")
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function_offsets = {"": 0}
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file_offsets = {"": 0}
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for address, name, filename in symbols:
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function_offset = intern_string(name, functions, function_offsets)
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file_offset = intern_string(filename, files, file_offsets)
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records.extend(struct.pack("<III", address, function_offset, file_offset))
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return (
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("dbg_sym_table", records),
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("dbg_fn_name_table", functions),
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("dbg_file_name_table", files),
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)
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def write_object(tables, output_file, objcopy, bfd_target):
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output = Path(output_file).absolute()
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with tempfile.TemporaryDirectory(prefix=".gen_fn_sym-", dir=output.parent) as directory:
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directory = Path(directory)
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name, data = tables[0]
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binary_path = directory / f"{name}.bin"
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binary_path.write_bytes(data)
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object_path = directory / "tables.o"
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stack_note_path = directory / "empty"
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stack_note_path.write_bytes(b"")
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command = [
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*objcopy,
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"--input-target", "binary",
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"--output-target", bfd_target.file_format,
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"--binary-architecture", bfd_target.architecture,
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"--rename-section", f".data=.{name},alloc,load,readonly,data,contents",
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"--set-section-alignment", ".data=4", "--strip-all",
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"--add-section", f".note.GNU-stack={stack_note_path}",
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]
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for name, data in tables[1:]:
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table_path = directory / f"{name}.bin"
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table_path.write_bytes(data)
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command.extend(["--add-section", f".{name}={table_path}"])
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command.extend(["--set-section-flags", f".{name}=alloc,load,readonly,data,contents"])
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for name, data in tables:
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command.extend(["--add-symbol", f"{name}=.{name}:0,global,object"])
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command.extend(["--add-symbol", f"{name}_end=.{name}:{len(data)},global"])
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run_tool([*command, str(binary_path), str(object_path)])
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os.replace(object_path, output)
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def main():
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parser = argparse.ArgumentParser(description="Generate a linkable kernel debug-symbol object using GNU binutils.")
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parser.add_argument("kernel_exec", help="kernel ELF binary")
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parser.add_argument("base_addr", type=lambda value: int(value, 0), help="kernel base address")
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parser.add_argument("source_cwd", help="build directory prefix to strip from source filenames")
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parser.add_argument("output_file", help="output object")
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parser.add_argument("--nm", type=tool_command, default=os.environ.get("NM", "nm"), help="GNU nm command (default: $NM or nm)")
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parser.add_argument("--objdump", type=tool_command, default=os.environ.get("OBJDUMP", "objdump"), help="GNU objdump command (default: $OBJDUMP or objdump)")
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parser.add_argument("--objcopy", type=tool_command, default=os.environ.get("OBJCOPY", "objcopy"), help="GNU objcopy command (default: $OBJCOPY or objcopy)")
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args = parser.parse_args()
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try:
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bfd_target = get_bfd_target(args.kernel_exec, args.objdump)
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symbols = collect_symbols(args.kernel_exec, args.base_addr, args.source_cwd, args.nm)
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tables = make_tables(symbols)
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write_object(tables, args.output_file, args.objcopy, bfd_target)
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except subprocess.CalledProcessError as error:
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parser.exit(1, f"{error.cmd[0]} failed: {error.stderr.strip()}\n")
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except (OSError, ValueError) as error:
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parser.exit(1, f"{error}\n")
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if __name__ == "__main__":
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main()
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