office-gobmx/compilerplugins/clang/pahole-all-classes.py

#!/usr/bin/python3
#
# Find holes in structures, so that we can pack them and improve our memory density.
#
# In order to make this work, you need to
# (1) Be operating in a workspace where you have a __NON-DEBUG__ build of LibreOffice, but __WITH SYMBOLS__.
#     (A debug build has different sizes for some things in the standard library.)
# (2) First run the unusedfields loplugin to generate a log file
# (3) Install the pahole stuff into your gdb, I used this one:
#     https://github.com/PhilArmstrong/pahole-gdb
# (4) Edit the loop near the top of the script to only produce results for one of our modules.
#     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
# (5) Run the script
#     ./compilerplugins/clang/pahole-all-classes.py > ./compilerplugins/clang/pahole.results
#

import _thread
import io
import os
import subprocess
import time
import re

# search for all the class names in the file produced by the unusedfields loplugin
#a = subprocess.Popen("grep 'definition:' workdir/loplugin.unusedfields.log | sort -u", stdout=subprocess.PIPE, shell=True)
a = subprocess.Popen("cat n1", stdout=subprocess.PIPE, shell=True)

classSet = set()
classSourceLocDict = dict()
with a.stdout as txt:
    for line in txt:
        tokens = line.decode('utf8').strip().split("\t")
        className = tokens[2].strip()
        srcLoc = tokens[5].strip()
        # ignore things like unions
        if "anonymous" in className: continue
        # ignore duplicates
        if className in classSet: continue
        classSet.add(className)
        classSourceLocDict[className] = srcLoc
a.terminate()

# Some of the pahole commands are going to fail, and I cannot read the error stream and the input stream
# together because python has no way of (easily) doing a non-blocking read.
# So I have to write the commands out using a background thread, and then read the entire resulting
# stream out below.
def write_pahole_commands(classes):
    for className in classes:
        stdin.write("echo " + className + " " + classSourceLocDict[className] + "\n")
        stdin.write("pahole " + className + "\n")
        stdin.flush()
    stdin.write("echo all-done\n")
    stdin.flush()
    stdin.close() # only way to make it flush the last echo command

# Use generator because lines often end up merged together in gdb's output, and we need
# to split them up, and that creates a mess in the parsing logic.
def read_generator(gdbOutput):
    while True:
        line = gdbOutput.readline().decode('utf8').strip()
        for split in line.split("(gdb)"):
            split = split.strip()
            if len(split) == 0: continue
            if "all-done" in split: return
            yield split

classList = sorted(classSet)

# Process 200 classes at a time, otherwise gdb's memory usage blows up and kills the machine
#
while len(classList) > 0:

    currClassList = classList[1:200];
    classList = classList[200:]

    gdbProc = subprocess.Popen("gdb", stdin=subprocess.PIPE, stdout=subprocess.PIPE, stderr=subprocess.STDOUT, shell=True)

    stdin = io.TextIOWrapper(gdbProc.stdin, 'utf-8')

    # make gdb load all the debugging info
    stdin.write("set confirm off\n")
    for filename in sorted(os.listdir('instdir/program')):
        if filename.endswith(".so"):
            stdin.write("add-symbol-file instdir/program/" + filename + "\n")
    stdin.flush()


    _thread.start_new_thread( write_pahole_commands, (currClassList,) )

    firstLineRegex = re.compile("/\*\s+(\d+)\s+\*/ struct")
    fieldLineRegex = re.compile("/\*\s+(\d+)\s+(\d+)\s+\*/ ")
    holeLineRegex = re.compile("/\* XXX (\d+) bit hole, try to pack \*/")
    # sometimes pahole can't determine the size of a sub-struct, and then it returns bad data
    bogusLineRegex = re.compile("/\*\s+\d+\s+0\s+\*/")
    structLines = list()
    foundHole = False
    cumulativeHoleBits = 0
    structSize = 0
    foundBogusLine = False
    # pahole doesn't report space at the end of the structure, so work it out myself
    sizeOfFields = 0
    for line in read_generator(gdbProc.stdout):
        structLines.append(line)
        firstLineMatch = firstLineRegex.match(line)
        if firstLineMatch:
            structSize = int(firstLineMatch.group(1))
        holeLineMatch = holeLineRegex.match(line)
        if holeLineMatch:
            foundHole = True
            cumulativeHoleBits += int(holeLineMatch.group(1))
        fieldLineMatch = fieldLineRegex.match(line)
        if fieldLineMatch:
            fieldSize = int(fieldLineMatch.group(2))
            sizeOfFields = int(fieldLineMatch.group(1)) + fieldSize
        if bogusLineRegex.match(line):
            foundBogusLine = True
        if line == "}":
            # Ignore very large structs, packing those is not going to help much, and
            # re-organising them can make them much less readable.
            if foundHole and len(structLines) < 12 and structSize < 100 and not foundBogusLine:
                # Verify that we have enough hole-space that removing it will result in a structure
                # that still satisfies alignment requirements, otherwise the compiler will just put empty
                # space at the end of the struct.
                # TODO improve detection of the required alignment for a structure
                potentialSpace = (cumulativeHoleBits / 8) + (sizeOfFields - structSize)
                if potentialSpace >= 8:
                    for line in structLines:
                        print(line)
                    if (sizeOfFields - structSize) > 0:
                        print("hole at end of struct: " + str(sizeOfFields - structSize))
            #  reset state
            structLines.clear()
            foundHole = False
            cumulativeHoleBits = 0
            structSize = 0
            foundBogusLine = False
            actualStructSize = 0

    gdbProc.terminate()