3 ms·

> Since go doesn’t inline assembly i decided to include the search loop into the assembly itself and to return the index of the non matching character. Sadly i

by ajross 2y ago

> Since go doesn’t inline assembly i decided to include the search loop into the assembly itself and to return the index of the non matching character. Sadly i didn’t get it to work fully because i’m missing tools to actually debug the assembly itself. Um... "gdb <my_binary>", "break <my_function>", "run", just like any other tool. Then "disassemble" to see the instructions around the PC, "stepi" to execute one instruction. "info register" to get current state (or use registers in an expression as e.g. "print $rax" or "print $r11"). And that's it. Debuggers are actually natively tools operating at the level of machine instructions. The language syntax support is a level on top.

xyzzy_plugh 2y ago
Assembly is one of those things that is feared by so many engineers, but is actually incredibly accessible. Whenever I find an excuse to drop down to assembly my colleagues have looked at me like I'm a wizard with 3 heads. The tooling to debug, dump or inspect, or to link or otherwise glue bits of assembly together has existed for decades. It's all right there!
- RicoElectrico 2y ago
  It's one of these areas LLMs really help to get started. Not much invention needed, but quite involved setup if you don't know what you're precisely looking for. Having them spit out boilerplate and needed invocations lowers the barrier substantially.
  - dragontamer 2y ago
    Assuming you have a C compiler, you should use C to get basic boilerplate and use asm or volatile asm to drop down to assembly level. This is true for GPUs, CPUs like x86 and ARM, and more. Only on the smallest of embedded systems like AVR with 4kB RAM have I ever found dropping to raw assembly to be useful. Bonus points: input/output/clobbers works well with the GCC and CLang optimizers. Though it's not intuitive how compilers can still move your assembly around, it's surprisingly full featured for how to get info into and out of registers. There are rare times where the C boilerplate is counterproductive. I guess OS level setup is another spot where raw non-C assembly is useful.
    - david-gpu 2y ago
      Intrinsics, when available, are a convenient tool. But even then, I think assembly these days has very limited applications and most programmers don't need to know any assembly to be effective. Preemptive disclaimer: all my jobs were the exception to the rule and I sadly had to work with various assembly languages on a daily basis. Still not a fan.
      - AlotOfReading 2y ago
        You should be able to read assembly, not least because understanding what's generated by the compiler or jit is pretty important to performance optimization.
        david-gpu 2y ago
        Aren't there many other steps with better bang for your buck to be done before that? Libraries, better algorithms and data structures, parallelism, etc.
        AlotOfReading 2y ago
        Reading assembly, like compiler explorer or in a debugger.
        david-gpu 2y ago
        Yes, I understand. But the only way that gives you good bang for your buck is if you have already exhausted a number of other areas earlier. I.e. it is marginal gains. How many programmers out there would be better served by spending time learning more about those other areas before they even start thinking about whether the compiler is generating slightly suboptimal assembly?
        boris-smidt 2y ago
        I suspect it depends, when you would write a yaml/json parser you can only change the algorithm up to a point. After that you will have to start doing some bit fiddling and then being able to see the assembly can be really valuable.
- dist1ll 2y ago
  I agree it's unnecessarily feared. At its core, it lacks a lot of complexity. But actually writing asm is an experience straight from the 80s. Compared to modern languages, the tooling is simply antiquated. I noticed this once I started writing larger sections of asm at a time. It's "fine" in the same sense that writing makefiles is "fine" - it becomes a PITA after a certain size. I think there's lots to improve on the current state of asm, but it's just too niche. The only power users I know are hobbyists working on operating systems and games for retro hardware.
  - boris-smidt 2y ago
    Also add cryptographical people to that list. A friend of mine told me that they create 'constant' time algorithms. These have to written in assembly otherwise the compiler will try to speed up the algorithm. But then you can theoretically measure the execution time of encrypting and reverse engineer the possible keys.
pm215 2y ago
I also like "disp /3i $pc", which tells gdb to disassemble the next three instructions whenever it stops (including after stepi). Though I'm sure you can configure it to give you more sophisticated disassembly display and context, especially with the tui interface, this is usually "good enough" for me when I run into something I want to step through at the assembly level in the middle of debugging a program that's primarily C.
- purplesyringa 2y ago
  On a related note, https://hugsy.github.io/gef/ https://hugsy.github.io/gef/ provides a TUI interface like that.

by ajross 2y ago

xyzzy_plugh 2y ago

Assembly is one of those things that is feared by so many engineers, but is actually incredibly accessible. Whenever I find an excuse to drop down to assembly my colleagues have looked at me like I'm a wizard with 3 heads. The tooling to debug, dump or inspect, or to link or otherwise glue bits of assembly together has existed for decades. It's all right there!

RicoElectrico 2y ago
It's one of these areas LLMs really help to get started. Not much invention needed, but quite involved setup if you don't know what you're precisely looking for. Having them spit out boilerplate and needed invocations lowers the barrier substantially.
- dragontamer 2y ago
  Assuming you have a C compiler, you should use C to get basic boilerplate and use asm or volatile asm to drop down to assembly level. This is true for GPUs, CPUs like x86 and ARM, and more. Only on the smallest of embedded systems like AVR with 4kB RAM have I ever found dropping to raw assembly to be useful. Bonus points: input/output/clobbers works well with the GCC and CLang optimizers. Though it's not intuitive how compilers can still move your assembly around, it's surprisingly full featured for how to get info into and out of registers. There are rare times where the C boilerplate is counterproductive. I guess OS level setup is another spot where raw non-C assembly is useful.
  - david-gpu 2y ago
    Intrinsics, when available, are a convenient tool. But even then, I think assembly these days has very limited applications and most programmers don't need to know any assembly to be effective. Preemptive disclaimer: all my jobs were the exception to the rule and I sadly had to work with various assembly languages on a daily basis. Still not a fan.
    - AlotOfReading 2y ago
      You should be able to read assembly, not least because understanding what's generated by the compiler or jit is pretty important to performance optimization.
      - david-gpu 2y ago
        Aren't there many other steps with better bang for your buck to be done before that? Libraries, better algorithms and data structures, parallelism, etc.
        AlotOfReading 2y ago
        Reading assembly, like compiler explorer or in a debugger.
        david-gpu 2y ago
        Yes, I understand. But the only way that gives you good bang for your buck is if you have already exhausted a number of other areas earlier. I.e. it is marginal gains. How many programmers out there would be better served by spending time learning more about those other areas before they even start thinking about whether the compiler is generating slightly suboptimal assembly?
        boris-smidt 2y ago
        I suspect it depends, when you would write a yaml/json parser you can only change the algorithm up to a point. After that you will have to start doing some bit fiddling and then being able to see the assembly can be really valuable.
dist1ll 2y ago
I agree it's unnecessarily feared. At its core, it lacks a lot of complexity. But actually writing asm is an experience straight from the 80s. Compared to modern languages, the tooling is simply antiquated. I noticed this once I started writing larger sections of asm at a time. It's "fine" in the same sense that writing makefiles is "fine" - it becomes a PITA after a certain size. I think there's lots to improve on the current state of asm, but it's just too niche. The only power users I know are hobbyists working on operating systems and games for retro hardware.
- boris-smidt 2y ago
  Also add cryptographical people to that list. A friend of mine told me that they create 'constant' time algorithms. These have to written in assembly otherwise the compiler will try to speed up the algorithm. But then you can theoretically measure the execution time of encrypting and reverse engineer the possible keys.

pm215 2y ago

I also like "disp /3i $pc", which tells gdb to disassemble the next three instructions whenever it stops (including after stepi). Though I'm sure you can configure it to give you more sophisticated disassembly display and context, especially with the tui interface, this is usually "good enough" for me when I run into something I want to step through at the assembly level in the middle of debugging a program that's primarily C.

purplesyringa 2y ago
On a related note, https://hugsy.github.io/gef/ https://hugsy.github.io/gef/ provides a TUI interface like that.