7 ms·

Lensm, a tool for viewing disassembly

156 points by jtolds 3y ago

vardump 3y ago
Wow, having to stare at disassembly too often, I really like this. Makes it much faster to follow branches and can easily see what instructions correspond to source code lines, even though it's not very exact at higher optimization levels. This should be integrated in all IDEs.
- mananaysiempre 3y ago
  With recent versions of GNU objdump, you can use --source --visualize-jumps=color and perhaps also --reloc or --dynamic-reloc for a similar experience with the native toolchain. (Unfortunately, -S/--source absolutely sucks for executables compiled at -O2.) Other tricks include --no-addresses --no-show-raw-insn, which make the disassembly decently diffable.
  - beeburrt 3y ago
    Nice. Thanks for the tip
- PhilipRoman 3y ago
  If you don't care about source lines, I find radare2 has a really good disassembler (in graph mode) It's meant for reverse engineering but I use it for debugging purposes too
c7DJTLrn 3y ago
It would probably be worth mentioning that this is for Go in the title.
- jcul 3y ago
  I'd imagine it would work for any binary with debug symbols, even though the tool is written in go? Though I haven't tried it, on mobile right now.
  - liamwire 3y ago
    I’m not so sure. From the article, the author mentions that they’re using an internal library from the Go compiler for the disassembly.
  - Conscat 3y ago
    Can it demangle non-Go identifiers?
  - vzaliva 3y ago
    I tried it with C and it does not work. So I guess it is go-specific indeed.
    - MobiusHorizons 3y ago
      Did you have debug symbols? I assume you probably passed -g, but the debug info can still not be compatible sometimes. I know when using lldb I sometimes have to force dwarf debug info or -ggdb to get it working.
    - jcul 3y ago
      Yeah I just tried it too. It did disassemble it and showed jumps, but no source code. It also didn't resolve calls to functions like printf.
  - egonelbre 3y ago
    Yeah, at the moment, unfortunately only works for Go. But implementing a different backend (e.g. llvm-symbolizer, objdump etc.) shouldn't be too difficult. The main things it needs to do are 1. list the decompilable symbols in the file, 2. disassemble and pull in the relevant source code. The UI part doesn't care whether it's Go or not.
deleted 3y ago
[deleted]
throwaway29303 3y ago
Previous threads about lensm https://news.ycombinator.com/item?id=32138111 https://news.ycombinator.com/item?id=32138111 - Lensm, a Tool for Viewing Disassembly (2022) https://news.ycombinator.com/item?id=32133394 https://news.ycombinator.com/item?id=32133394 - Lensm: Go Assembly and Source Viewer (2022)
speps 3y ago
Looks a lot like the P4Merge diffing window: https://www.perforce.com/manuals/p4merge/Content/P4Merge/diff-merge.text_diff.html https://www.perforce.com/manuals/p4merge/Content/P4Merge/dif...
brancz 3y ago
Love lensm! I've used it on several occasions to teach people about inlining, bounds check removals, and other performance related topics that are best highlighted by actually seeing differences in assembly. I find it's easier for people to understand what is actually happening under the hood than just tell them "do this and it's faster". I also highly recommend following the creator. I'm always impressed with anything Egon creates.
djmips 3y ago
I like the name, it reminds me of Lensman - the classic sci-fi series that inspired the first video game Spacewar!
fitz-re 3y ago
This would be great for reversing tools such as IDA and Binary Ninja!

156 points by jtolds 3y ago

Wow, having to stare at disassembly too often, I really like this. Makes it much faster to follow branches and can easily see what instructions correspond to source code lines, even though it's not very exact at higher optimization levels. This should be integrated in all IDEs.

mananaysiempre 3y ago
With recent versions of GNU objdump, you can use --source --visualize-jumps=color and perhaps also --reloc or --dynamic-reloc for a similar experience with the native toolchain. (Unfortunately, -S/--source absolutely sucks for executables compiled at -O2.) Other tricks include --no-addresses --no-show-raw-insn, which make the disassembly decently diffable.
- beeburrt 3y ago
  Nice. Thanks for the tip
PhilipRoman 3y ago
If you don't care about source lines, I find radare2 has a really good disassembler (in graph mode) It's meant for reverse engineering but I use it for debugging purposes too

c7DJTLrn 3y ago

It would probably be worth mentioning that this is for Go in the title.

jcul 3y ago
I'd imagine it would work for any binary with debug symbols, even though the tool is written in go? Though I haven't tried it, on mobile right now.
- liamwire 3y ago
  I’m not so sure. From the article, the author mentions that they’re using an internal library from the Go compiler for the disassembly.
- Conscat 3y ago
  Can it demangle non-Go identifiers?
- vzaliva 3y ago
  I tried it with C and it does not work. So I guess it is go-specific indeed.
  - MobiusHorizons 3y ago
    Did you have debug symbols? I assume you probably passed -g, but the debug info can still not be compatible sometimes. I know when using lldb I sometimes have to force dwarf debug info or -ggdb to get it working.
  - jcul 3y ago
    Yeah I just tried it too. It did disassemble it and showed jumps, but no source code. It also didn't resolve calls to functions like printf.
- egonelbre 3y ago
  Yeah, at the moment, unfortunately only works for Go. But implementing a different backend (e.g. llvm-symbolizer, objdump etc.) shouldn't be too difficult. The main things it needs to do are 1. list the decompilable symbols in the file, 2. disassemble and pull in the relevant source code. The UI part doesn't care whether it's Go or not.

deleted 3y ago

[deleted]

throwaway29303 3y ago

Previous threads about lensm https://news.ycombinator.com/item?id=32138111 https://news.ycombinator.com/item?id=32138111 - Lensm, a Tool for Viewing Disassembly (2022) https://news.ycombinator.com/item?id=32133394 https://news.ycombinator.com/item?id=32133394 - Lensm: Go Assembly and Source Viewer (2022)

speps 3y ago

Looks a lot like the P4Merge diffing window: https://www.perforce.com/manuals/p4merge/Content/P4Merge/diff-merge.text_diff.html https://www.perforce.com/manuals/p4merge/Content/P4Merge/dif...

brancz 3y ago

Love lensm! I've used it on several occasions to teach people about inlining, bounds check removals, and other performance related topics that are best highlighted by actually seeing differences in assembly. I find it's easier for people to understand what is actually happening under the hood than just tell them "do this and it's faster". I also highly recommend following the creator. I'm always impressed with anything Egon creates.

djmips 3y ago

I like the name, it reminds me of Lensman - the classic sci-fi series that inspired the first video game Spacewar!

fitz-re 3y ago

This would be great for reversing tools such as IDA and Binary Ninja!