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LLDB: Extend the dump_page methods #4420

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merged 3 commits into from
Apr 27, 2021
Merged

LLDB: Extend the dump_page methods #4420

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e0632cb
lldb: Add Freelist Index to dump_page output
eightbitraptor Apr 27, 2021
28cb836
lldb: dump_page_rvalue - dump a heap page containing an RVALUE
eightbitraptor Apr 27, 2021
5d2e409
lldb: highlight the slot when using dump_page_rvalue
eightbitraptor Apr 27, 2021
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87 changes: 74 additions & 13 deletions misc/lldb_cruby.py
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Original file line number Diff line number Diff line change
Expand Up @@ -527,10 +527,68 @@ def dump_bits(target, result, page, object_address, end = "\n"):
check_bits(page, "wb_unprotected_bits", bitmap_index, bitmap_bit, "U"),
), end=end, file=result)

def dump_page(debugger, command, result, internal_dict):
class HeapPageIter:
def __init__(self, page, target):
self.page = page
self.target = target
self.start = page.GetChildMemberWithName('start').GetValueAsUnsigned();
self.num_slots = page.GetChildMemberWithName('total_slots').unsigned
self.counter = 0
self.tRBasic = target.FindFirstType("struct RBasic")
self.tRValue = target.FindFirstType("struct RVALUE")

def __iter__(self):
return self

def __next__(self):
if self.counter < self.num_slots:
obj_addr_i = self.start + (self.counter * self.tRValue.GetByteSize())
obj_addr = lldb.SBAddress(obj_addr_i, self.target)
slot_info = (self.counter, obj_addr_i, self.target.CreateValueFromAddress("object", obj_addr, self.tRBasic))
self.counter += 1

return slot_info
else:
raise StopIteration


def dump_page_internal(page, target, process, thread, frame, result, debugger, highlight=None):
if not ('RUBY_Qfalse' in globals()):
lldb_init(debugger)

ruby_type_map = ruby_types(debugger)

freelist = []
fl_start = page.GetChildMemberWithName('freelist').GetValueAsUnsigned()
tRVALUE = target.FindFirstType("struct RVALUE")

while fl_start > 0:
freelist.append(fl_start)
obj_addr = lldb.SBAddress(fl_start, target)
obj = target.CreateValueFromAddress("object", obj_addr, tRVALUE)
fl_start = obj.GetChildMemberWithName("as").GetChildMemberWithName("free").GetChildMemberWithName("next").GetValueAsUnsigned()

for (page_index, obj_addr, obj) in HeapPageIter(page, target):
dump_bits(target, result, page, obj_addr, end= " ")
flags = obj.GetChildMemberWithName('flags').GetValueAsUnsigned()
flType = flags & RUBY_T_MASK

flidx = ' '
if flType == RUBY_T_NONE:
try:
flidx = "%3d" % freelist.index(obj_addr)
except ValueError:
flidx = ' '
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It looks like objects that are not T_NONE will get an empty { } in the output for flidx. I think this is some confusing output for objects that are not T_NONE.

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Yup, that was the intended behaviour. It allows you to easily visualise which slots are part of the freelist and which ones aren't. Like this:

bits: [     ] T_NONE     [401]: {  2} Addr: 0x1007ebed0 (flags: 0x0)
bits: [     ] T_NONE     [402]: {  1} Addr: 0x1007ebef8 (flags: 0x0)
bits: [     ] T_NONE     [403]: {  0} Addr: 0x1007ebf20 (flags: 0x0)
bits: [LM   ] T_CLASS    [404]: {   } Addr: 0x1007ebf48 (flags: 0x100001062)
bits: [LM   ] T_PAYLOAD  [405]: {   } Addr: 0x1007ebf70 (flags: 0x3077)

It's easy to see where slots have been assigned values and where the freelist pointer (and list) is going. Although I suspect we could make it more obvious in the output that { } was the freelist index? How about:

bits: [     ] T_NONE     idx: [401] freelist_idx: {  2} Addr: 0x1007ebed0 (flags: 0x0)
bits: [     ] T_NONE     idx: [402] freelist_idx: {  1} Addr: 0x1007ebef8 (flags: 0x0)
bits: [     ] T_NONE     idx: [403] freelist_idx: {  0} Addr: 0x1007ebf20 (flags: 0x0)
bits: [LM   ] T_CLASS    idx: [404] freelist_idx: {   } Addr: 0x1007ebf48 (flags: 0x100001062)
bits: [LM   ] T_PAYLOAD  idx: [405] freelist_idx: {   } Addr: 0x1007ebf70 (flags: 0x3077)

the empty { } mirrors the behaviour of rp - it shows an empty [ ] section when no bits are set

bits: [     ]
T_NONE: (RBasic) *$35 = (flags = 0x0000000000000000, klass = 0x00000001007ebea8)

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I like your second one 👍

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👍 I'll patch that and push it up.


result_str = "%s idx: [%3d] freelist_idx: {%s} Addr: %0#x (flags: %0#x)" % (rb_type(flags, ruby_type_map), page_index, flidx, obj_addr, flags)

if highlight == obj_addr:
result_str = ' '.join([result_str, "<<<<<"])

print(result_str, file=result)


def dump_page(debugger, command, result, internal_dict):
target = debugger.GetSelectedTarget()
process = target.GetProcess()
thread = process.GetSelectedThread()
Expand All @@ -540,21 +598,23 @@ def dump_page(debugger, command, result, internal_dict):
page = frame.EvaluateExpression(command)
page = page.Cast(tHeapPageP)

tRBasic = target.FindFirstType("struct RBasic")
tRValue = target.FindFirstType("struct RVALUE")
dump_page_internal(page, target, process, thread, frame, result, debugger)

obj_address = page.GetChildMemberWithName('start').GetValueAsUnsigned();
num_slots = page.GetChildMemberWithName('total_slots').unsigned

ruby_type_map = ruby_types(debugger)
def dump_page_rvalue(debugger, command, result, internal_dict):
target = debugger.GetSelectedTarget()
process = target.GetProcess()
thread = process.GetSelectedThread()
frame = thread.GetSelectedFrame()

val = frame.EvaluateExpression(command)
page = get_page(lldb, target, val)
page_type = target.FindFirstType("struct heap_page").GetPointerType()
page.Cast(page_type)

dump_page_internal(page, target, process, thread, frame, result, debugger, highlight=val.GetValueAsUnsigned())


for j in range(0, num_slots):
offset = obj_address + (j * tRValue.GetByteSize())
obj_addr = lldb.SBAddress(offset, target)
p = target.CreateValueFromAddress("object", obj_addr, tRBasic)
dump_bits(target, result, page, offset, end = " ")
flags = p.GetChildMemberWithName('flags').GetValueAsUnsigned()
print("%s [%3d]: Addr: %0#x (flags: %0#x)" % (rb_type(flags, ruby_type_map), j, offset, flags), file=result)

def rb_type(flags, ruby_types):
flType = flags & RUBY_T_MASK
Expand Down Expand Up @@ -586,6 +646,7 @@ def __lldb_init_module(debugger, internal_dict):
debugger.HandleCommand("command script add -f lldb_cruby.heap_page_body heap_page_body")
debugger.HandleCommand("command script add -f lldb_cruby.rb_backtrace rbbt")
debugger.HandleCommand("command script add -f lldb_cruby.dump_page dump_page")
debugger.HandleCommand("command script add -f lldb_cruby.dump_page_rvalue dump_page_rvalue")

lldb_init(debugger)
print("lldb scripts for ruby has been installed.")