unjit

Overview

Features

• disassemble code from a living process;

• based on LLVM disassembler;

• by default disassemble all (JITed) subprograms found in /tmp/perf-$pid.map;

• symbolication of JIT-ed symbols using /tmp/perf-$pid.map;

• symbolication of AOT symbols using ELF SHT_SYMTAB and SHT_DYNSYM sections;

• does not ptrace, does not stop the process;

• output similar to the output of objdump and compatible with what Linux perf expects.

Compatibility

• currently working on Linux 3.2 (process_vm_readv()) and a suitable libc

Limitations

• Currently do not decompile code which does not have an associated symbol.

Usage

Basic usage

unjit -p $pid> dis.txt

1. Find the JIT-ed function from a process from /tmp/perf-$pid.map;

2. Read the corresponding instructions from the remote process memory;

3. Disassemble them to stdout.

Using with perf

perf top -p $pid --objdump ./perfobjdump

Discussion

Linux perf map (/tmp/perf-${pid}.map)

The /tmp/perf-${pid}.map is a file used by JIT compilers to tell Linux perf the location and name of JITed subprograms. The format is:

$startAddressInHexa $sizeInHexa $name

Example:

41f3ae82 34 foo
41f3aec6 52 bar

Roadmap

Without any specific order:

• better detection of modules (DT_DEBUG);

• disassemble by symbol name;

• symbolicate GOT and PLT addresses;

• load symbols from DT_SYMTAB;

• load symbols from DWARF (optional);

• load DWARF info from a separate file;

• do not hardcode the CPU model (CLI option);

• select the native CPU model by default;

• Capstone support.