Python scripting
This will give more flexibility than GDB scripting to achieve your crazy ideas.
The main problem here, just like with GDB scripts, is that this will likely be too slow for most applications without target hardware support, e.g.: a C hello world takes 1 minute for only 18k instructions.
gdb.py
class TraceAsm(gdb.Command):
def __init__(self):
super().__init__(
'trace-asm',
gdb.COMMAND_BREAKPOINTS,
gdb.COMPLETE_NONE,
False
)
def invoke(self, argument, from_tty):
argv = gdb.string_to_argv(argument)
if argv:
gdb.write('Does not take any arguments.\n')
else:
done = False
thread = gdb.inferiors()[0].threads()[0]
last_path = None
last_line = None
with open('trace.tmp', 'w') as f:
while thread.is_valid():
frame = gdb.selected_frame()
sal = frame.find_sal()
symtab = sal.symtab
if symtab:
path = symtab.fullname()
line = sal.line
else:
path = None
line = None
if path != last_path:
f.write("path {}{}".format(path, os.linesep))
last_path = path
if line != last_line:
f.write("line {}{}".format(line, os.linesep))
last_line = line
pc = frame.pc()
f.write("{} {} {}".format(hex(pc), frame.architecture().disassemble(pc)[0]['asm'], os.linesep))
gdb.execute('si', to_string=True)
TraceAsm()
GitHub upstream.
main.S
global _start
_start:
; Write.
mov rax, 1
mov rdi, 1
mov rsi, hello_world
mov rdx, hello_world_len
syscall
; Exit.
mov rax, 60
mov rdi, 0
syscall
hello_world db "hello world", 10
hello_world_len equ $ - hello_world
GitHub upstream.
Assemble and run:
as -o main.o main.S
ld -o main.out main.o
gdb -nh -batch -ex 'source ~/test/gdb.py' -ex 'starti' -ex 'trace-asm' ./main.out
cat trace.tmp
Output:
0x401000 mov $0x1,%rax
0x401007 mov $0x1,%rdi
0x40100e mov $0x402000,%rsi
0x401015 mov $0xc,%rdx
0x40101c syscall
0x40101e mov $0x3c,%rax
0x401025 mov $0x0,%rdi
0x40102c syscall
QEMU emulation
Edit: -d in_asm alone shows only translation chunks, so if a chunk gets executed multiple times, it won't show multiple times. There are some extra flags that make it more accurate, see: What instructions does qemu trace? QEMU's exec_tb trace backend might however do it: How to use QEMU's simple trace backend?
This performed much faster than the GDB python solution, the C hello works runs instantaneously! However, the log was only 10k instructions long instead of 18k on the same executable, so it must be skipping something that normally gets run TODO understand.
E.g. in user mode simulation:
qemu-x86_64 -d in_asm ./main.out
Output:
warning: TCG doesn't support requested feature: CPUID.01H:ECX.vmx [bit 5]
----------------
IN:
0x0000000000401000: mov $0x1,%rax
0x0000000000401007: mov $0x1,%rdi
0x000000000040100e: mov $0x402000,%rsi
0x0000000000401015: mov $0xc,%rdx
0x000000000040101c: syscall
hello world
----------------
IN:
0x000000000040101e: mov $0x3c,%rax
0x0000000000401025: mov $0x0,%rdi
0x000000000040102c: syscall
See also.
Tested in Ubuntu 18.10, GDB 8.2, QEMU 2.12.0.
