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!addsym Windbg - IDA Symbol extension Redux

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!addsym Windbg - IDA Symbol extension Redux

Post by Kayaker »

!addsym Windbg - IDA Symbol extension Redux

Once upon a time in days of yore, a young hobbit created a Windbg extension of great value and mystery, forged in hardship and sacrifice, and was all but forgotten.

This is to be a retelling of that tale and where it takes us today.

It begins with a blog post by Blabberer six years ago and ends with my rebuilding of the extension in Visual Studio 2013 and the results.

viewtopic.php?f=46&t=15503-addsym-windb ... to-windbg)

I think this extension is a great idea, I'd like to see it evolve. I'm having a problem, some of the symbols are loaded into Windbg but not all and not correctly.

The extension was borrowed by at least two others, with credit, one with a few minor changes and another released as an IDAPython script

Adds IDA symbols as WinDbg synthetic symbols

IDAScript to create Symbol file which can be loaded in WinDbg via AddSyntheticSymbol


I started with the EngExtCpp-style extension sample project extcpp.cpp provided in the Windows Kits 8.1 x64, and popped it into VisualStudio 2013. First step was to Upgrade VC++ Compilers
changing Platform Toolset to 'v120' (was 'v110').

Then I copied Blabs extension code (ikonst updated) and added it to the sample project as another export EXT_COMMAND_METHOD(addsym);

The only compile issue I really had was this one

extcpp.cpp(96): error C2678: binary '!=' : no operator found which takes a left-hand operand of type
'std::basic_istream<char,std::char_traits<char>>' (or there is no acceptable conversion)

The error was underlined on the != character on 2 similar lines:

while (getline(ifs, inbuff) != NULL);

The error code doc is here
https://docs.microsoft.com/en-us/cpp/er ... ew=vs-2019

Something to do with the left hand side being a const object, a function declared in <string>, and the value != NULL on the right hand side.

This is wacky C++. I read various solutions involving namespaces, overloading, nothing I wanted to hear or understood. Finally realized that in this case at least, the while{} statement could be changed to eliminate the comparison completely with

} while (getline(ifs, inbuff));

What the hell, the return value NULL is no good with strings?

Anyway, that pretty much fixed it and I could compile the Windbg extension as x32 or x64.


Next step was to create the .idasym file from the IDC script. It's purpose is to transfer the Names ida generated to windbg. I also took that as meaning to include user-defined functions and perhaps variable names. The EngExtCpp extension uses AddSyntheticSymbol to accomplish that.

The idc script itself parses names as such:
symname = Name( segstart+i ) ;

It works as expected, though the code could be modified to exclude certain segments from analysis for example. I don't think it picks up user-defined variable names. The python version above only picks up name changes that you prefix with something, so it limits the symbols to only what you might want.

I did make one change, rather than hardcoding the directory where the .idasym file will be created I used this to just create it in the same IDA exe/database folder:
symfile = GetInputFilePath() + ".idasym";

The .idasym file seems to be correct in producing a list of "names", but the problem seems to be that not all of them are imported into Windbg.


As an example, I disassembled Strings64.exe and renamed the first 2 functions to see if they would be transferred to Windbg.

Code: Select all

.load myextcpp.dll

0:000> .chain
Extension DLL search Path:
    C:\Program Files (x86)\Windows Kits\8.1\Debuggers\x64\winext
Extension DLL chain:
    myextcpp.dll: image 6.3.9600.17336, API 1.0.0, built Mon Apr 27 00:44:48 2020
        [path: C:\Program Files (x86)\Windows Kits\8.1\Debuggers\x64\winext\myextcpp.dll]

0:000> !addsym /?  // btw I didn't know that's how you called the damned built in EngExtCpp help!!

!addsym <MODULE> <path>
  <MODULE> - An expression or address like nt / 0x804d7000 
  <path> - path to idasym file 
           viz c:\idasym\MODULE.EXT.idasym (consumes remainder of input string)
windbg extension to use names that are generated by ida 
do .reload /f MODULE.ext=base,size prior to using this extension

// .reload [Options] [Module [= Address [, Size [, 
0:000> .reload /f image00000001_3f420000.exe=000000013f420000,29000
*** ERROR: Module load completed but symbols could not be loaded for image00000001_3f420000.exe

Note that Strings64.exe is called 'image00000001_3f420000' by Windbg, for some reason it doesn't recognize the process name and uses its base address as an image name.

0:000> lm
start             end                 module name
00000001`3f420000 00000001`3f449000   image00000001_3f420000   (no symbols)    

0:000> !myextcpp.addsym image00000001_3f420000 C:\Utilities\Strings\Strings64.exe.idasym

total symbols in idasym file is 1321 press ctrl+break to interrupt symbol resolving 
500 symbols resolved
1000 symbols resolved
total 1321 symbols resolved 
Good up until this point but here's the beginning addresses of what symbols were imported, only starting at 3f4313e8, which is somewhere in a random proc in the middle of the file, in the middle of an opcode no less, then it starts with names in the .idata section.

0:000> x image00000001_3f420000!*
00000001`3f4313e8 image00000001_3f420000!_positive = <no type information>
00000001`3f433000 image00000001_3f420000!RegQueryValueExW = <no type information>
00000001`3f433008 image00000001_3f420000!RegQueryValueExA = <no type information>

Here are the first 5 lines from the .idasym file, where it should have started to import symbols:


I had a similar problem with a compiled x32 extension on a win32 app, it only began importing names from the .idata section

0:000> x winid!*
00436000 winid!RegQueryValueExA = <no type information>

OK, that's too much writing for now, but I wanted to go over everything I did, and figure out what I did wrong.

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Posts: 1535
Joined: Wed Dec 08, 2004 11:12 am

Post by blabberer »

It Was completely 32bit then (IDAFREE5 ,WIN7X86 , vcvars32 windbg32)

it seems you are testing 64bit so did you recompile the src for x64

yes checking for NULL isn't recommended (string::getline(istream,string) returns a void* converted to a bool so checked for NULL
passed compilation in old compilers newer version don't accept it

what you did By removing the != NULL is the right construct

if you are hell bent on writing super duper error checking read this excellent article

anyway I just recompiled it vs2017 x64 (as usual I use the dev cmd prompt in vscode terminal ) and it seems to work properly

created a new directory and copied the existing src def and bat files

Code: Select all

mkdir addsym64
cd addsym64
copy ..\addsym\addsym.cpp .\addsym64.cpp
copy ..\addsym\addsym.def .\addsym64.def
copied two bat files  one to initialize vs one to compile and link extension
dir contents

Code: Select all

:\>dir /b

added help EXPORTS to addsym64.def and renamed EXPORT addsym to addsym64

Code: Select all

diff addsym64.def ..\addsym\addsym.def
<       help
<     addsym64
>     addsym

included engextcpp.cpp instead of engextcpp.hpp to avoid implementing the mandatory exports (init,uninit,notify,help) in addsym64.cpp

renamed command from addsym to addsym64

removed the != NULL part

Code: Select all

diff addsym64.cpp ..\addsym\addsym.cpp
< #include <engextcpp.cpp>
> #include <engextcpp.hpp>
<     EXT_COMMAND_METHOD(addsym64);
>     EXT_COMMAND_METHOD(addsym);
<     addsym64,
>     addsym,
<     } while (getline(ifs, inbuff));
>     } while (getline(ifs, inbuff) != NULL);
<     while (getline(fs, buff))
>     while (getline(fs, buff) != NULL)
the contents of runvs.bat

Code: Select all

:\>cat runvs64.bat
%comspec% /k "C:\Program Files (x86)\Microsoft Visual Studio\2017\Community\VC\Auxiliary\Build\vcvars64.bat"
the contents of bld.bat

Code: Select all

:\>cat bld.bat
@ECHO off
set INCLUDE=%INCLUDE%;C:\Program Files (x86)\Windows Kits\10\Debuggers\inc
set LIB=%LIB%;C:\Program Files (x86)\Windows Kits\10\Debuggers\lib
set LINKLIBS=dbgeng.lib

cl /LD /Zi /W4  /EHsc /nologo /Od %1.cpp /link /RELEASE /DEF:addsym64.def %LINKLIBS%
we are ready to compile and link a 64 bit extension

Code: Select all


:\>C:\WINDOWS\system32\cmd.exe /k "C:\Program Files (x86)\Microsoft Visual Studio\2017\Community\VC\Auxiliary\Build\vcvars64.bat"
** Visual Studio 2017 Developer Command Prompt v15.9.22
** Copyright (c) 2017 Microsoft Corporation
[vcvarsall.bat] Environment initialized for: 'x64'

:\>bld.bat addsym64
C:\Program Files (x86)\Windows Kits\10\Debuggers\inc\engextcpp.cpp(1849): warning C4245: 'argument': conversion from 'int' to 'ULONG64', signed/unsigned mismatch
   Creating library addsym64.lib and object addsym64.exp

:\>dir /s /b *.dll
ok it built it seems lets test

open strings.exe in idafree 7 run the idc

creating idasym file c:\IDASYM\strings64.exe.idasym

Code: Select all

:\>cdb -c ".load .\addsym64.dll;!addsym64 strings64 c:\idasym\strings64.exe.idasym;x strings64!main;q" f:\sysint\strings64.exe | f:\git\usr\bin\awk.exe "/Reading/,/quit/"
0:000> cdb: Reading initial command '.load .\addsym64.dll;!addsym64 strings64 c:\idasym\strings64.exe.idasym;x strings64!main;q'
total symbols in idasym file is 1319 press ctrl+break to interrupt symbol resolving
*** ERROR: Module load completed but symbols could not be loaded for f:\sysint\strings64.exe
500 symbols resolved
1000 symbols resolved
total 1319 symbols resolved
00007ff6`2cc03310 strings64!main = <no type information>


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Post by Kayaker »

Well that works great now on an x64 app! I went back and used your original code, which I apologize for not doing first. I had used the ikonst version which was said to be modified to work with kernel drivers whereas the original code did not (which doesn't really make sense considering your example in the blog post), but I guess it didn't work for me. I haven't tried a kernel driver yet. This was all done with IDA 7 free on Win7.

Functions as well as variables renamed in IDA now show up as symbols in Windbg, very useful. Nice work Blabs :)
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Posts: 1000
Joined: Tue Apr 06, 2004 11:00 am

Re: !addsym Windbg - IDA Symbol extension Redux

Post by WaxfordSqueers »

Just wondering if the extensions in 0cchext.dll are similar, like !dsym? Not the 0cchext.dll in the windbg directory, the 0cchext at this github addy. The file is twice the size of the one in the windbg\ext directory.

I think Blabbs may have pointed me to this extension since it has a !hwnd extension.

https://github.com/0cch/0cchext/release ... .
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