Tag: Symbols

Just as the previous post about stripping symbols from a Mach-O binary, here’s one about stripping them from an ELF binary.

The syntax to execute the script is the same as in the previous post, only the called function changes:

cerpro -c -r path/to/strip.py:stripELF source destination

Here’s the code:

from Pro.Core import *
from Pro.ELF import *

def stripELF(srcname, dstname):
    oldc = createContainerFromFile(srcname)
    if oldc.isNull():
        print("error: couldn't open '%s'" % (srcname,))
        return
    obj = ELFObject()
    if not obj.Load(oldc):
        print("error: could't load ELF")
        return
    newc = oldc.copyToNewContainer()

    sects = obj.Sections()

    count = 0
    it = obj.SymbolTableSections().iterator()
    it.next()
    while it.hasNext():
        s = sects.At(it.next())
        # only the .symtab section
        if s.Num("sh_type") != 2:
            continue
        strtaboffs = sects.At(s.Num("sh_link")).Num("sh_offset")
        sit = obj.Symbols(s).iterator()
        while sit.hasNext():
            sym = sit.next()
            # only local symbols
            if sym.Num("st_shndx") == 0:
                continue
            nameoffs = sym.Num("st_name") + strtaboffs
            name, ret = obj.ReadUInt8String(nameoffs, 0x10000)
            newc.fill(nameoffs, 0, len(name))
            count += 1

    if newc.save(dstname):
        print("successfully stripped all %d local symbols!" % (count,))
    else:
        print("error: couldn't save stripped binary to '%s'" % (dstname,))

That’s it!

And here again the complete script which you can use to strip both a Mach-O and an ELF binary.

# strip.py

from Pro.Core import *
from Pro.MachO import *
from Pro.ELF import *

def stripMachO(srcname, dstname):
    oldc = createContainerFromFile(srcname)
    if oldc.isNull():
        print("error: couldn't open '%s'" % (srcname,))
        return
    obj = MachObject()
    if not obj.Load(oldc):
        print("error: could't load Mach-O")
        return
    obj.ProcessLoadCommands()
    newc = oldc.copyToNewContainer()

    symlc = obj.SymTableLC()
    stroffs = symlc.Num("stroff")

    count = 0
    it = obj.SymbolNList(symlc).iterator()
    while it.hasNext():
        syms = it.next()
        # only local symbols
        if syms.Num("sect") == 0:
            continue
        nameoffs = obj.AddressToOffset(syms.Num("strx") + stroffs)
        name, ret = obj.ReadUInt8String(nameoffs, 0x10000)
        newc.fill(nameoffs, 0, len(name))
        count += 1

    if newc.save(dstname):
        print("successfully stripped all %d local symbols!" % (count,))
    else:
        print("error: couldn't save stripped binary to '%s'" % (dstname,))

def stripELF(srcname, dstname):
    oldc = createContainerFromFile(srcname)
    if oldc.isNull():
        print("error: couldn't open '%s'" % (srcname,))
        return
    obj = ELFObject()
    if not obj.Load(oldc):
        print("error: could't load ELF")
        return
    newc = oldc.copyToNewContainer()

    sects = obj.Sections()

    count = 0
    it = obj.SymbolTableSections().iterator()
    it.next()
    while it.hasNext():
        s = sects.At(it.next())
        # only the .symtab section
        if s.Num("sh_type") != 2:
            continue
        strtaboffs = sects.At(s.Num("sh_link")).Num("sh_offset")
        sit = obj.Symbols(s).iterator()
        while sit.hasNext():
            sym = sit.next()
            # only local symbols
            if sym.Num("st_shndx") == 0:
                continue
            nameoffs = sym.Num("st_name") + strtaboffs
            name, ret = obj.ReadUInt8String(nameoffs, 0x10000)
            newc.fill(nameoffs, 0, len(name))
            count += 1

    if newc.save(dstname):
        print("successfully stripped all %d local symbols!" % (count,))
    else:
        print("error: couldn't save stripped binary to '%s'" % (dstname,))

The Linux x64 version of Profiler should be released soon. So stay tuned!

A common mistake many developers do is to leave names of local symbols inside applications built on OS X. Using the strip utility combined with the compiler visibility flags is, unfortunately, not enough.

So I wrote a small script for Profiler to be run from the command line and I integrated it in the build process.

The syntax to execute the script is:

cerpro -c -r path/to/strip.py:stripMachO source destination

Here’s the whole code:

# name: strip.py

from Pro.Core import *
from Pro.MachO import *

def stripMachO(srcname, dstname):
    oldc = createContainerFromFile(srcname)
    if oldc.isNull():
        print("error: couldn't open '%s'" % (srcname,))
        return
    obj = MachObject()
    if not obj.Load(oldc):
        print("error: could't load Mach-o")
        return
    obj.ProcessLoadCommands()
    newc = oldc.copyToNewContainer()

    symlc = obj.SymTableLC()
    stroffs = symlc.Num("stroff")

    it = obj.SymbolNList(symlc).iterator()
    while it.hasNext():
        syms = it.next()
        # only local symbols
        if syms.Num("sect") == 0:
            continue
        nameoffs = obj.AddressToOffset(syms.Num("strx") + stroffs)
        name, ret = obj.ReadUInt8String(nameoffs, 0x10000)
        newc.fill(nameoffs, 0, len(name))

    if newc.save(dstname):
        print("successfully stripped all local symbols!")
    else:
        print("error: couldn't save stripped binary to '%s'" % (dstname,))

The code zeroes names of symbols which are not associated to any section in the binary.

Easy. 🙂