compilerplugins/clang/pahole-all-classes.py

   1 #!/usr/bin/python3
   2 #
   3 # Find holes in structures, so that we can pack them and improve our memory density.
   4 #
   5 # In order to make this work, you need to
   6 # (1) Be operating in a workspace where you have a __NON-DEBUG__ build of LibreOffice, but __WITH SYMBOLS__.
   7 #     (A debug build has different sizes for some things in the standard library.)
   8 # (2) First run the unusedfields loplugin to generate a log file
   9 # (3) Install the pahole stuff into your gdb, I used this one:
  10 #     https://github.com/PhilArmstrong/pahole-gdb
  11 # (4) Edit the loop near the top of the script to only produce results for one of our modules.
  12 #     Note that this will make GDB soak up about 8G of RAM, which is why I don't do more than one module at a time
  13 # (5) Run the script
  14 #     ./compilerplugins/clang/pahole-all-classes.py > ./compilerplugins/clang/pahole.results
  15 #
  16
  17 import _thread
  18 import io
  19 import os
  20 import subprocess
  21 import time
  22 import re
  23
  24 # search for all the class names in the file produced by the unusedfields loplugin
  25 #a = subprocess.Popen("grep 'definition:' workdir/loplugin.unusedfields.log | sort -u", stdout=subprocess.PIPE, shell=True)
  26 a = subprocess.Popen("cat ../libo/n1", stdout=subprocess.PIPE, shell=True)
  27
  28 classSourceLocDict = dict()
  29 classSet = set()
  30 with a.stdout as txt:
  31     for line in txt:
  32         tokens = line.decode('utf8').strip().split("\t")
  33         className = tokens[2].strip()
  34         srcLoc = tokens[5].strip()
  35         # ignore things like unions
  36         if "anonymous" in className: continue
  37         # ignore duplicates
  38         if className in classSet: continue
  39         # for now, just check the stuff in /sc/inc
  40         if srcLoc.startswith("a"):
  41             classSourceLocDict[srcLoc] = className
  42             classSet.add(className)
  43 a.terminate()
  44
  45 gdbProc = subprocess.Popen("gdb", stdin=subprocess.PIPE, stdout=subprocess.PIPE, stderr=subprocess.STDOUT, shell=True)
  46
  47 stdin = io.TextIOWrapper(gdbProc.stdin, 'utf-8')
  48
  49 # make gdb load all the debugging info
  50 stdin.write("set confirm off\n")
  51 for filename in sorted(os.listdir('instdir/program')):
  52     if filename.endswith(".so"):
  53         stdin.write("add-symbol-file instdir/program/" + filename + "\n")
  54 stdin.flush()
  55
  56
  57 # Some of the pahole commands are going to fail, and I cannot read the error stream and the input stream
  58 # together because python has no way of (easily) doing a non-blocking read.
  59 # So I have to write the commands out using a background thread, and then read the entire resulting
  60 # stream out below.
  61 def write_pahole_commands():
  62     for srcLoc in sorted(classSourceLocDict.keys()):
  63         className = classSourceLocDict[srcLoc]
  64         stdin.write("echo " + className + " " + srcLoc + "\n")
  65         stdin.write("pahole " + className + "\n")
  66         stdin.flush()
  67     stdin.write("echo all-done\n")
  68     stdin.flush()
  69     stdin.close() # only way to make it flush the last echo command
  70
  71 _thread.start_new_thread( write_pahole_commands, () )
  72
  73 # Use generator because lines often end up merged together in gdb's output, and we need
  74 # to split them up, and that creates a mess in the parsing logic.
  75 def read_generator():
  76     while True:
  77         line = gdbProc.stdout.readline().decode('utf8').strip()
  78         for split in line.split("(gdb)"):
  79             split = split.strip()
  80             if len(split) == 0: continue
  81             if "all-done" in split: return
  82             yield split
  83
  84 firstLineRegex = re.compile("/\*\s+(\d+)\s+\*/ struct")
  85 fieldLineRegex = re.compile("/\*\s+(\d+)\s+(\d+)\s+\*/ ")
  86 holeLineRegex = re.compile("/\* XXX (\d+) bit hole, try to pack \*/")
  87 # sometimes pahole can't determine the size of a sub-struct, and then it returns bad data
  88 bogusLineRegex = re.compile("/\*\s+\d+\s+0\s+\*/")
  89 structLines = list()
  90 foundHole = False
  91 cumulativeHoleBits = 0
  92 structSize = 0
  93 foundBogusLine = False
  94 # pahole doesn't report space at the end of the structure, so work it out myself
  95 sizeOfFields = 0
  96 for line in read_generator():
  97     structLines.append(line)
  98     firstLineMatch = firstLineRegex.match(line)
  99     if firstLineMatch:
 100         structSize = int(firstLineMatch.group(1))
 101     holeLineMatch = holeLineRegex.match(line)
 102     if holeLineMatch:
 103         foundHole = True
 104         cumulativeHoleBits += int(holeLineMatch.group(1))
 105     fieldLineMatch = fieldLineRegex.match(line)
 106     if fieldLineMatch:
 107         fieldSize = int(fieldLineMatch.group(2))
 108         sizeOfFields = int(fieldLineMatch.group(1)) + fieldSize
 109     if bogusLineRegex.match(line):
 110         foundBogusLine = True
 111     if line == "}":
 112         # Ignore very large structs, packing those is not going to help much, and
 113         # re-organising them can make them much less readable.
 114         if foundHole and len(structLines) < 12 and structSize < 100 and not foundBogusLine:
 115             # Verify that we have enough hole-space that removing it will result in a structure
 116             # that still satisfies alignment requirements, otherwise the compiler will just put empty
 117             # space at the end of the struct.
 118             # TODO improve detection of the required alignment for a structure
 119             potentialSpace = (cumulativeHoleBits / 8) + (sizeOfFields - structSize)
 120             if potentialSpace >= 8:
 121                 for line in structLines:
 122                     print(line)
 123                 if (sizeOfFields - structSize) > 0:
 124                     print("hole at end of struct: " + str(sizeOfFields - structSize))
 125         #  reset state
 126         structLines.clear()
 127         foundHole = False
 128         cumulativeHoleBits = 0
 129         structSize = 0
 130         foundBogusLine = False
 131         actualStructSize = 0
 132
 133 gdbProc.terminate()