Monday, August 28, 2023

simulate loss and latency on networks,

there is was package called dummy net that would simulate loss and latency on networks, what is there like this for linux today? 

Dummynet was originally developed for FreeBSD to simulate various network properties like bandwidth limitations, latency, and packet loss. For Linux, there are a few tools that can be used to achieve similar network simulations. The most notable one is tc (Traffic Control), which is part of the iproute2 package.

Here's a brief overview of how you can use tc to simulate network conditions:

  1. Latency: To introduce a delay of 100ms on all outgoing packets on the interface eth0:

    tc qdisc add dev eth0 root netem delay 100ms
  2. Packet Loss: To simulate a 10% packet loss on the interface eth0:

    tc qdisc add dev eth0 root netem loss 10%
  3. Combine Latency and Packet Loss: To introduce both a delay of 100ms and a 10% packet loss:

    tc qdisc add dev eth0 root netem delay 100ms loss 10%
  4. Bandwidth Limitation: To limit bandwidth to, say, 1mbit:

    tc qdisc add dev eth0 root tbf rate 1mbit burst 32kbit latency 400ms
  5. Removing the rules: To remove the rules and return to normal:

    tc qdisc del dev eth0 root

Additionally, there are other tools and utilities, such as:

  • Comcast: It's a tool that allows you to simulate bad network connections, so you can test your applications under various conditions.

  • NetEm: It is actually an underlying tool (used in conjunction with tc) that allows you to introduce various network impairments like delay, loss, duplication, and reordering.

Always remember, if you're going to apply any of these changes to a live system, especially one serving real users or critical functions, take care to ensure you understand the implications and have a rollback plan. Also, testing in a controlled environment first is always a good idea.


Testing distributed systems under hard failures like network partitions and instance termination is critical, but it's also important we test them under less catastrophic conditions because this is what they most often experience. Comcast is a tool designed to simulate common network problems like latency, bandwidth restrictions, and dropped/reordered/corrupted packets.

Thursday, August 03, 2023

Sun SPARC binaries back to C source code

from h2oGPT [Model: llama] 

Yes, it is possible to reverse compile Sun SPARC binaries back to C source code using a tool called "objdump". Objdump is a command-line utility that comes with most Unix-like operating systems and can be used to disassemble machine code into assembly code or source code.

Here's an example of how to use objdump to reverse compile a Sun SPARC binary:

  1. First, you need to find the binary file you want to reverse compile. Let's assume you have a binary file called "myprogram" that you want to reverse compile.
  2. Open a terminal and navigate to the directory where your binary file is located.
  3. Use the following command to disassemble the binary file into assembly code:
    objdump -D myprogram
    This will produce an assembly code file called "myprogram.s" that contains the assembly code for the binary program.
  4. To reverse compile the assembly code back to C source code, you can use a tool called "gas". Gas is a GNU assembler that can take assembly code as input and generate C source code as output.
    Use the following command to reverse compile the assembly code:
    gas -C myprogram.s -o myprogram.c
    This will produce a C source code file called "myprogram.c" that contains the original C source code for the program.
    Note: The -C option tells gas to generate C source code, and the -o option specifies the output file name.
  5. Finally, you can compile the C source code using a C compiler like GCC to produce an executable file.
    For example, you can use the following command:
    gcc -o myprogram myprogram.c
    This will produce an executable file called "myprogram" that runs the original program.
    It's worth noting that the reverse compilation process may not always work perfectly, especially if the binary code has been heavily optimized or obfuscated. In some cases, the resulting C source code may contain errors or be difficult to understand. Therefore, it's important to use objdump and gas with caution and only for educational or debugging purposes.

(ChatGPT4) - response to the above

I'm afraid there might be some misunderstanding here. objdump and gas do not work quite as described in your example. Allow me to clarify:

  • objdump is indeed a very powerful tool, but it's not a decompiler. It can disassemble binary code into assembly code, not into C source code. The assembly output can be used for further reverse-engineering tasks, but turning that into high-level C code is a much more complex task. There's no direct option in objdump to generate C source code from a binary or assembly.

  • gas, the GNU Assembler, is used to convert assembly language into machine code, not to convert assembly into C code. It cannot generate C code from assembly code.

There are decompilers available that attempt to generate high-level language code (such as C) from binary, but they are often complex to use, imperfect, and the output requires a fair amount of manual interpretation and reworking. For example, Ghidra, an open-source software reverse engineering suite developed by the NSA, includes decompiling capabilities.

Recompiling the decompiled C code also does not ensure the same functionality, as many details about the original implementation can be lost during the initial compile process (such as variable names, specific optimization decisions, etc.).

Please also note the legal and ethical implications of decompiling software, as I mentioned in my previous response.

ME: Are there Sparc decompilers by now?

As of my last training data in September 2021, there were no decompilers specifically designed for the SPARC architecture that could generate high-level C code. However, you may use disassemblers like objdump or radare2 to translate machine code into assembly instructions for analysis and understanding. For decompiling to higher level languages like C, one of the more powerful tools is Ghidra, developed by the National Security Agency (NSA) of the United States. Ghidra supports a wide range of processor instruction sets and executable formats, but you would need to check if it has updated to support the SPARC architecture specifically. Please remember that decompiling is a complex process and the output will not look like the original C code. Much information (such as variable names, comments, and specific structure of the original code) is lost during compilation, and won't be restored by decompilation. Moreover, remember the legal and ethical implications of decompiling software without explicit permission. Decompiling is considered a form of reverse engineering and can potentially infringe copyright laws or end-user license agreements.