Print a program's arguments, environment, and ELF aux vector with GDB

showstack.py

"""Print a program's arguments, environment, and ELF aux vector with GDB

Run with:

    gdb-multiarch -n -q -batch -ex 'source showstack.py'
"""

from __future__ import print_function

import gdb
from gdb import Breakpoint

# From glibc/elf/elf.h
_ATS = {
    "AT_NULL": 0,
    "AT_IGNORE": 1,
    "AT_EXECFD": 2,
    "AT_PHDR": 3,
    "AT_PHENT": 4,
    "AT_PHNUM": 5,
    "AT_PAGESZ": 6,
    "AT_BASE": 7,
    "AT_FLAGS": 8,
    "AT_ENTRY": 9,
    "AT_NOTELF": 10,
    "AT_UID": 11,
    "AT_EUID": 12,
    "AT_GID": 13,
    "AT_EGID": 14,
    "AT_CLKTCK": 17,
    "AT_PLATFORM": 15,
    "AT_HWCAP": 16,
    "AT_FPUCW": 18,
    "AT_DCACHEBSIZE": 19,
    "AT_ICACHEBSIZE": 20,
    "AT_UCACHEBSIZE": 21,
    "AT_IGNOREPPC": 22,
    "AT_SECURE": 23,
    "AT_BASE_PLATFORM": 24,
    "AT_RANDOM": 25,
    "AT_HWCAP2": 26,
    "AT_EXECFN": 31,
    "AT_SYSINFO": 32,
    "AT_SYSINFO_EHDR": 33,
    "AT_L1I_CACHESHAPE": 34,
    "AT_L1D_CACHESHAPE": 35,
    "AT_L2_CACHESHAPE": 36,
    "AT_L3_CACHESHAPE": 37,
    "AT_L1I_CACHESIZE": 40,
    "AT_L1I_CACHEGEOMETRY": 41,
    "AT_L1D_CACHESIZE": 42,
    "AT_L1D_CACHEGEOMETRY": 43,
    "AT_L2_CACHESIZE": 44,
    "AT_L2_CACHEGEOMETRY": 45,
    "AT_L3_CACHESIZE": 46,
    "AT_L3_CACHEGEOMETRY": 47,
    "AT_MINSIGSTKSZ": 51,
}
_ATS_REVERSE = {v: k for (k, v) in _ATS.items()}

_LIBC_START_MAIN = "__libc_start_main"

_CHAR_STAR = gdb.lookup_type("char").pointer()
_INT = gdb.lookup_type("int")


def header(s):
    print()
    print(s)
    print("-"*len(s))


def show_stack():
    frame = gdb.newest_frame()
    assert frame.is_valid()
    assert frame.type() == gdb.NORMAL_FRAME

    header("ARGUMENTS")
    argc = frame.read_register("r1")
    argv = frame.read_register("r2").cast(_CHAR_STAR.pointer())
    print("argc", "=", argc)
    for index in range(argc):
        print("arg", index, "=", (argv + index).dereference().string())

    header("ENVIRONMENT")
    envp = argv + argc + 1
    try:
        while True:
            envvar = envp.dereference().string()
            assert "=" in envvar
            print(envvar)
            envp += 1
    except gdb.MemoryError:
        pass

    header("AUX VECTOR")
    # 1 = inclusive upper bound, where lower bound is 0
    auxvp = (envp + 1).cast(_INT.array(1).pointer())
    while True:
        auxv_entry = auxvp.dereference()
        ty = int(auxv_entry[0])
        print(_ATS_REVERSE[ty], "=", "{0:#x}".format(int(auxv_entry[1])))
        auxvp += 1
        if ty == _ATS["AT_NULL"]:
            break


gdb.execute("set arch arm")
gdb.execute("set endian little")
gdb.execute("target remote localhost:12345")

class MyBreakpoint(Breakpoint):
    def stop(self):
        show_stack()

breakpoint = MyBreakpoint(_LIBC_START_MAIN)
assert breakpoint.is_valid()
breakpoint.enabled = True
assert breakpoint.enabled is True

gdb.execute("continue")