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Part of my daily job involves getting dirty at the assembler level, generally to debug segfaults, FPE, deadlocks and similar stuff. It's a fascinating challenge which makes me feel extremely powerful and in control of the hard, low-level technicalities of the OS, libraries and hardware I use. Most of my effort, however, would be impossible without a few tools I learned to appreciate and love through hours of solid dependency. I'm posting them here, and while the list is certainly not exhaustive, it's a starting kit for the hardcore debugger.

Linux

c++filt

This nifty utility converts C++ mangled symbols into the unmangled form. A simple example is the following

$ c++filt _ZNK3MPI4File19Get_position_sharedEv
MPI::File::Get_position_shared() const

More complex symbols can become unreadable in the mangled form, especially when they arise from template instantiation. A quick pass with c++filt will make everything much clearer.

pmap

Another nifty utility in the Linux arsenal, this easy program reports the VM layout of a running process.

$ pmap  21102
21102:   cat
0000000000400000     44K r-x--  /bin/cat
000000000060a000      4K r----  /bin/cat
000000000060b000      4K rw---  /bin/cat
0000000001969000    132K rw---    [ anon ]
00007f3b98aa9000   7068K r----  /usr/lib/locale/locale-archive
00007f3b99190000   1748K r-x--  /lib/x86_64-linux-gnu/libc-2.15.so
00007f3b99345000   2048K -----  /lib/x86_64-linux-gnu/libc-2.15.so
00007f3b99545000     16K r----  /lib/x86_64-linux-gnu/libc-2.15.so
00007f3b99549000      8K rw---  /lib/x86_64-linux-gnu/libc-2.15.so
00007f3b9954b000     20K rw---    [ anon ]
00007f3b99550000    136K r-x--  /lib/x86_64-linux-gnu/ld-2.15.so
00007f3b99749000     12K rw---    [ anon ]
00007f3b99770000      8K rw---    [ anon ]
00007f3b99772000      4K r----  /lib/x86_64-linux-gnu/ld-2.15.so
00007f3b99773000      8K rw---  /lib/x86_64-linux-gnu/ld-2.15.so
00007fff18ae9000    136K rw---    [ stack ]
00007fff18bff000      4K r-x--    [ anon ]
ffffffffff600000      4K r-x--    [ anon ]
 total            11404K

To achieve the same with a post-mortem core file, the gdb commands "info files" and "maintenance info sections" are your friends. When running, "info proc mappings" can achieve the same.

lddtree

lddtree is like ldd, but it traverses the full hierarchy, building a tree diagram of all dependencies. It is available on Ubuntu in the package pax-utils.

$ lddtree /bin/ls
ls => /bin/ls (interpreter => /lib64/ld-linux-x86-64.so.2)
    libselinux.so.1 => /lib/i386-linux-gnu/libselinux.so.1
        libdl.so.2 => /lib/i386-linux-gnu/libdl.so.2
        ld-linux.so.2 => /lib/i386-linux-gnu/ld-linux.so.2
    librt.so.1 => /lib/i386-linux-gnu/librt.so.1
        libpthread.so.0 => /lib/i386-linux-gnu/libpthread.so.0
    libacl.so.1 => /lib/x86_64-linux-gnu/libacl.so.1
        libattr.so.1 => /lib/x86_64-linux-gnu/libattr.so.1
    libc.so.6 => /lib/i386-linux-gnu/libc.so.6

Windows

I am not a Windows person, but I build and debug on it rather often. With time, I gathered a few essential tools to understand the source of your problems during build, deployment and execution.

Process monitor

Reports events of different nature from all the processes in your system, such as disk access, registry access, and so on. I found this utility fundamental to track a strange crash that occurred in a third party closed-source library. The problem turned out to be an attempt to write to a directory that was not writable. From the website:

Process Monitor is an advanced monitoring tool for Windows that shows real-time file system, Registry and process/thread activity. It combines the features of two legacy Sysinternals utilities, Filemon and Regmon, and adds an extensive list of enhancements including rich and non-destructive filtering, comprehensive event properties such session IDs and user names, reliable process information, full thread stacks with integrated symbol support for each operation, simultaneous logging to a file, and much more. Its uniquely powerful features will make Process Monitor a core utility in your system troubleshooting and malware hunting toolkit.

Process Explorer

An equivalent of fuser on Linux. From the website:

Ever wondered which program has a particular file or directory open? Now you can find out. Process Explorer shows you information about which handles and DLLs processes have opened or loaded.

VMMap

Extremely useful tool to see the Virtual Memory layout. It is precious to check potential fragmentation scenarios that could lead to invalid allocations.

From the website:

VMMap is a process virtual and physical memory analysis utility. It shows a breakdown of a process's committed virtual memory types as well as the amount of physical memory (working set) assigned by the operating system to those types. Besides graphical representations of memory usage, VMMap also shows summary information and a detailed process memory map.

Dependency walker

Performs more or less the task of lddtree on Linux and otool on Mac. It's invaluable to figure our which libraries or symbols are unresolved. I soon discovered that Windows is not very verbose when it comes to unresolved dependencies at startup. From the website:

Dependency Walker is a free utility that scans any 32-bit or 64-bit Windows module (exe, dll, ocx, sys, etc.) and builds a hierarchical tree diagram of all dependent modules. For each module found, it lists all the functions that are exported by that module, and which of those functions are actually being called by other modules. Another view displays the minimum set of required files, along with detailed information about each file including a full path to the file, base address, version numbers, machine type, debug information, and more.

Event Viewer

Provided on a standard windows 7 installation. Another invaluable tool to understand what's going on in your program, reports error and anomalous conditions that prevent an application to start, and much more.


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