# This implements the "diagnose-nsstring" command, usually installed in the debug session like
# command script import lldb.diagnose
# it is used when NSString summary formatter fails to replicate the logic that went into LLDB making the
# decisions it did and providing some useful context information that can
# be used for improving the formatter
import lldb
def read_memory(process, location, size):
data = ""
error = lldb.SBError()
for x in range(0, size - 1):
byte = process.ReadUnsignedFromMemory(x + location, 1, error)
if error.fail:
data = data + "err%s" % "" if x == size - 2 else ":"
else:
try:
data = data + "0x%x" % byte
if byte == 0:
data = data + "(\\0)"
elif byte == 0xA:
data = data + "(\\a)"
elif byte == 0xB:
data = data + "(\\b)"
elif byte == 0xC:
data = data + "(\\c)"
elif byte == "\n":
data = data + "(\\n)"
else:
data = data + "(%s)" % chr(byte)
if x < size - 2:
data = data + ":"
except Exception as e:
print(e)
return data
def diagnose_nsstring_Command_Impl(debugger, command, result, internal_dict):
"""
A command to diagnose the LLDB NSString data formatter
invoke as
(lldb) diagnose-nsstring <expr returning NSString>
e.g.
(lldb) diagnose-nsstring @"Hello world"
"""
target = debugger.GetSelectedTarget()
process = target.GetProcess()
thread = process.GetSelectedThread()
frame = thread.GetSelectedFrame()
if not target.IsValid() or not process.IsValid():
return "unable to get target/process - cannot proceed"
options = lldb.SBExpressionOptions()
options.SetFetchDynamicValue()
error = lldb.SBError()
if frame.IsValid():
nsstring = frame.EvaluateExpression(command, options)
else:
nsstring = target.EvaluateExpression(command, options)
print(str(nsstring), file=result)
nsstring_address = nsstring.GetValueAsUnsigned(0)
if nsstring_address == 0:
return "unable to obtain the string - cannot proceed"
expression = "\
struct $__lldb__notInlineMutable {\
char* buffer;\
signed long length;\
signed long capacity;\
unsigned int hasGap:1;\
unsigned int isFixedCapacity:1;\
unsigned int isExternalMutable:1;\
unsigned int capacityProvidedExternally:1;\n\
#if __LP64__\n\
unsigned long desiredCapacity:60;\n\
#else\n\
unsigned long desiredCapacity:28;\n\
#endif\n\
void* contentsAllocator;\
};\
\
struct $__lldb__CFString {\
void* _cfisa;\
uint8_t _cfinfo[4];\
uint32_t _rc;\
union {\
struct __inline1 {\
signed long length;\
} inline1;\
struct __notInlineImmutable1 {\
char* buffer;\
signed long length;\
void* contentsDeallocator;\
} notInlineImmutable1;\
struct __notInlineImmutable2 {\
char* buffer;\
void* contentsDeallocator;\
} notInlineImmutable2;\
struct $__lldb__notInlineMutable notInlineMutable;\
} variants;\
};\
"
expression = expression + "*(($__lldb__CFString*) %d)" % nsstring_address
# print expression
dumped = target.EvaluateExpression(expression, options)
print(str(dumped), file=result)
little_endian = target.byte_order == lldb.eByteOrderLittle
ptr_size = target.addr_size
info_bits = (
dumped.GetChildMemberWithName("_cfinfo")
.GetChildAtIndex(0 if little_endian else 3)
.GetValueAsUnsigned(0)
)
is_mutable = (info_bits & 1) == 1
is_inline = (info_bits & 0x60) == 0
has_explicit_length = (info_bits & (1 | 4)) != 4
is_unicode = (info_bits & 0x10) == 0x10
is_special = (
nsstring.GetDynamicValue(lldb.eDynamicCanRunTarget).GetTypeName()
== "NSPathStore2"
)
has_null = (info_bits & 8) == 8
print(
"\nInfo=%d\nMutable=%s\nInline=%s\nExplicit=%s\nUnicode=%s\nSpecial=%s\nNull=%s\n"
% (
info_bits,
"yes" if is_mutable else "no",
"yes" if is_inline else "no",
"yes" if has_explicit_length else "no",
"yes" if is_unicode else "no",
"yes" if is_special else "no",
"yes" if has_null else "no",
),
file=result,
)
explicit_length_offset = 0
if not has_null and has_explicit_length and not is_special:
explicit_length_offset = 2 * ptr_size
if is_mutable and not is_inline:
explicit_length_offset = explicit_length_offset + ptr_size
elif is_inline:
pass
elif not is_inline and not is_mutable:
explicit_length_offset = explicit_length_offset + ptr_size
else:
explicit_length_offset = 0
if explicit_length_offset == 0:
print("There is no explicit length marker - skipping this step\n", file=result)
else:
explicit_length_offset = nsstring_address + explicit_length_offset
explicit_length = process.ReadUnsignedFromMemory(
explicit_length_offset, 4, error
)
print(
"Explicit length location is at 0x%x - read value is %d\n"
% (explicit_length_offset, explicit_length),
file=result,
)
if is_mutable:
location = 2 * ptr_size + nsstring_address
location = process.ReadPointerFromMemory(location, error)
elif (
is_inline
and has_explicit_length
and not is_unicode
and not is_special
and not is_mutable
):
location = 3 * ptr_size + nsstring_address
elif is_unicode:
location = 2 * ptr_size + nsstring_address
if is_inline:
if not has_explicit_length:
print(
"Unicode & Inline & !Explicit is a new combo - no formula for it",
file=result,
)
else:
location += ptr_size
else:
location = process.ReadPointerFromMemory(location, error)
elif is_special:
location = nsstring_address + ptr_size + 4
elif is_inline:
location = 2 * ptr_size + nsstring_address
if not has_explicit_length:
location += 1
else:
location = 2 * ptr_size + nsstring_address
location = process.ReadPointerFromMemory(location, error)
print("Expected data location: 0x%x\n" % (location), file=result)
print(
"1K of data around location: %s\n" % read_memory(process, location, 1024),
file=result,
)
print(
"5K of data around string pointer: %s\n"
% read_memory(process, nsstring_address, 1024 * 5),
file=result,
)
def __lldb_init_module(debugger, internal_dict):
debugger.HandleCommand(
"command script add -o -f %s.diagnose_nsstring_Command_Impl diagnose-nsstring"
% __name__
)
print(
'The "diagnose-nsstring" command has been installed, type "help diagnose-nsstring" for detailed help.'
)
__lldb_init_module(lldb.debugger, None)
__lldb_init_module = None
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