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# gdb script: identify the vtable slot that returns 999 in ctx bring-up.
#
# Run #3 found the failing store at file 0x275cec: the indirect call at
# 0x275ce6, slot +0x4580 of the table at [ctx+0x40], called with
# (ctx, r15+0xb8), returned 0x3e7. The table slot is installed by one of the
# architecture vtable installers; this script prints the runtime target so it
# can be mapped to its decompiled body, plus the call arguments.
#
# Run: sudo gdb -p <cdt-pid> -batch -x /tmp/bpz4.py
import gdb
import time
out = gdb.execute("info proc mappings", to_string=True)
base = None
for line in out.splitlines():
if "libcuda" in line and "r-xp" in line:
f = line.split()
base = int(f[0], 16) - int(f[3], 16)
break
print("BASE=0x%x" % (base or 0))
if base is None:
print("NO_LIBCUDA")
raise SystemExit
gdb.execute("set pagination off")
gdb.execute("set confirm off")
for off in (0x275ce6, 0x275cec):
gdb.execute("break *0x%x" % (base + off))
t0 = time.time()
for hit in range(20):
try:
gdb.execute("continue")
except gdb.error as e:
print("CONTINUE_END %s" % e)
break
rip = int(gdb.parse_and_eval("$rip")) & 0xffffffffffffffff
off = rip - base
print("HIT %d t=%.3f off=0x%x" % (hit, time.time() - t0, off))
try:
r12 = int(gdb.parse_and_eval("$r12")) & 0xffffffffffffffff
r15 = int(gdb.parse_and_eval("$r15")) & 0xffffffffffffffff
vec = int(gdb.parse_and_eval("*(unsigned long *)0x%x" % (r12 + 0x40)))
tgt = int(gdb.parse_and_eval("*(unsigned long *)0x%x" % (vec + 0x4580)))
print(" r12=0x%x r15=0x%x vec=0x%x TARGET=0x%x target_off=0x%x" %
(r12, r15, vec, tgt, tgt - base))
print(" r15+0xb8 words: " + gdb.execute(
"x/8gx 0x%x" % (r15 + 0xb8), to_string=True).strip())
except Exception as e:
print(" deref_fail %s" % e)
if off == 0x275cec:
try:
print(" call returned eax=0x%x" % (int(gdb.parse_and_eval("$rax")) & 0xffffffff))
except Exception:
pass
try:
print(gdb.execute("bt 8", to_string=True))
except Exception as e:
print("bt_fail %s" % e)
try:
gdb.execute("detach")
except Exception:
pass
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