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#!/usr/bin/env python3
# This Source Code Form is subject to the terms of the Mozilla Public
# License, v. 2.0. If a copy of the MPL was not distributed with this
# From a scan mode DMD log, extract some information about a
# particular block, such as its allocation stack or which other blocks
# contain pointers to it. This can be useful when investigating leaks
# caused by unknown references to refcounted objects.
import argparse
import gzip
import json
import re
import sys
# The DMD output version this script handles.
outputVersion = 5
# If --ignore-alloc-fns is specified, stack frames containing functions that
# match these strings will be removed from the *start* of stack traces. (Once
# we hit a non-matching frame, any subsequent frames won't be removed even if
# they do match.)
allocatorFns = [
"malloc (",
"replace_malloc",
"replace_calloc",
"replace_realloc",
"replace_memalign",
"replace_posix_memalign",
"malloc_zone_malloc",
"moz_xmalloc",
"moz_xcalloc",
"moz_xrealloc",
"operator new(",
"operator new[](",
"g_malloc",
"g_slice_alloc",
"callocCanGC",
"reallocCanGC",
"vpx_malloc",
"vpx_calloc",
"vpx_realloc",
"vpx_memalign",
"js_malloc",
"js_calloc",
"js_realloc",
"pod_malloc",
"pod_calloc",
"pod_realloc",
"nsTArrayInfallibleAllocator::Malloc",
"Allocator<ReplaceMallocBase>::malloc(",
"mozilla::dmd::StackTrace::Get(",
"mozilla::dmd::AllocCallback(",
"mozilla::dom::DOMArena::Allocate(",
# This one necessary to fully filter some sequences of allocation functions
# that happen in practice. Note that ??? entries that follow non-allocation
# functions won't be stripped, as explained above.
"???",
]
####
# Command line arguments
def range_1_24(string):
value = int(string)
if value < 1 or value > 24:
msg = "{:s} is not in the range 1..24".format(string)
raise argparse.ArgumentTypeError(msg)
return value
parser = argparse.ArgumentParser(
description="Analyze the heap graph to find out things about an object. \
By default this prints out information about blocks that point to the given block."
)
parser.add_argument("dmd_log_file_name", help="clamped DMD log file name")
parser.add_argument("block", help="address of the block of interest")
parser.add_argument(
"--info",
dest="info",
action="store_true",
default=False,
help="Print out information about the block.",
)
parser.add_argument(
"-sfl",
"--max-stack-frame-length",
type=int,
default=300,
help="Maximum number of characters to print from each stack frame",
)
parser.add_argument(
"-a",
"--ignore-alloc-fns",
action="store_true",
help="ignore allocation functions at the start of traces",
)
parser.add_argument(
"-f",
"--max-frames",
type=range_1_24,
default=8,
help="maximum number of frames to consider in each trace",
)
parser.add_argument(
"-c",
"--chain-reports",
action="store_true",
help="if only one block is found to hold onto the object, report "
"the next one, too",
)
####
class BlockData:
def __init__(self, json_block):
self.addr = json_block["addr"]
if "contents" in json_block:
contents = json_block["contents"]
else:
contents = []
self.contents = []
for c in contents:
self.contents.append(int(c, 16))
self.req_size = json_block["req"]
self.alloc_stack = json_block["alloc"]
def print_trace_segment(args, stacks, block):
(traceTable, frameTable) = stacks
for l in traceTable[block.alloc_stack]:
# The 5: is to remove the bogus leading "#00: " from the stack frame.
print(" " + frameTable[l][5 : args.max_stack_frame_length])
def show_referrers(args, blocks, stacks, block):
visited = set([])
anyFound = False
while True:
referrers = {}
for b, data in blocks.items():
which_edge = 0
for e in data.contents:
if e == block:
# 8 is the number of bytes per word on a 64-bit system.
# XXX This means that this output will be wrong for logs from 32-bit systems!
referrers.setdefault(b, []).append(8 * which_edge)
anyFound = True
which_edge += 1
for r in referrers:
sys.stdout.write(
"0x{} size = {} bytes".format(blocks[r].addr, blocks[r].req_size)
)
plural = "s" if len(referrers[r]) > 1 else ""
print(
" at byte offset"
+ plural
+ " "
+ (", ".join(str(x) for x in referrers[r]))
)
print_trace_segment(args, stacks, blocks[r])
print("")
if args.chain_reports:
if len(referrers) == 0:
sys.stdout.write("Found no more referrers.\n")
break
if len(referrers) > 1:
sys.stdout.write("Found too many referrers.\n")
break
sys.stdout.write("Chaining to next referrer.\n\n")
for r in referrers:
block = r
if block in visited:
sys.stdout.write("Found a loop.\n")
break
visited.add(block)
else:
break
if not anyFound:
print("No referrers found.")
def show_block_info(args, blocks, stacks, block):
b = blocks[block]
sys.stdout.write("block: 0x{}\n".format(b.addr))
sys.stdout.write("requested size: {} bytes\n".format(b.req_size))
sys.stdout.write("\n")
sys.stdout.write("block contents: ")
for c in b.contents:
v = "0" if c == 0 else blocks[c].addr
sys.stdout.write("0x{} ".format(v))
sys.stdout.write("\n\n")
sys.stdout.write("allocation stack:\n")
print_trace_segment(args, stacks, b)
return
def cleanupTraceTable(args, frameTable, traceTable):
# Remove allocation functions at the start of traces.
if args.ignore_alloc_fns:
# Build a regexp that matches every function in allocatorFns.
escapedAllocatorFns = map(re.escape, allocatorFns)
fn_re = re.compile("|".join(escapedAllocatorFns))
# Remove allocator fns from each stack trace.
for traceKey, frameKeys in traceTable.items():
numSkippedFrames = 0
for frameKey in frameKeys:
frameDesc = frameTable[frameKey]
if re.search(fn_re, frameDesc):
numSkippedFrames += 1
else:
break
if numSkippedFrames > 0:
traceTable[traceKey] = frameKeys[numSkippedFrames:]
# Trim the number of frames.
for traceKey, frameKeys in traceTable.items():
if len(frameKeys) > args.max_frames:
traceTable[traceKey] = frameKeys[: args.max_frames]
def loadGraph(options):
# Handle gzipped input if necessary.
isZipped = options.dmd_log_file_name.endswith(".gz")
opener = gzip.open if isZipped else open
with opener(options.dmd_log_file_name, "rb") as f:
j = json.load(f)
if j["version"] != outputVersion:
raise Exception("'version' property isn't '{:d}'".format(outputVersion))
block_list = j["blockList"]
blocks = {}
for json_block in block_list:
blocks[int(json_block["addr"], 16)] = BlockData(json_block)
traceTable = j["traceTable"]
frameTable = j["frameTable"]
cleanupTraceTable(options, frameTable, traceTable)
return (blocks, (traceTable, frameTable))
def analyzeLogs():
options = parser.parse_args()
(blocks, stacks) = loadGraph(options)
block = int(options.block, 16)
if block not in blocks:
print("Object " + options.block + " not found in traces.")
print("It could still be the target of some nodes.")
return
if options.info:
show_block_info(options, blocks, stacks, block)
return
show_referrers(options, blocks, stacks, block)
if __name__ == "__main__":
analyzeLogs()