LTO is not working, again

[pacak]

Hi, I'm having this issue trying to run the tool with https://github.com/louis-e/arnis. I've disabled the (Tauri) GUI feature, so in theory it's just a CLI application with ~500 dependencies.

❯ rustup show
Default host: x86_64-unknown-linux-gnu
rustup home:  /home/benjamin/.rustup

stable-x86_64-unknown-linux-gnu (default)
rustc 1.84.0 (9fc6b4312 2025-01-07)

❯ cargo asm --version
Version: 0.2.47

❯ cargo asm --bin arnis --no-default-features

<lots of output since it is compiling...>

Error: Cannot locate the path to the asm file

The current version of cargo-show-asm works in a brand-new cargo new foo project, but it doesn't work here. What's going on?

Originally posted by @benjamin051000 in #82

[pacak]

Blocked on cargo rust-lang/cargo#13672

[pacak]

Thin LTO for arnis crate makes rustc to produce about 950 .s files:

arnis-3243b349208c302c.8qi3mr8qju3xmfjsf34x3m992.rcgu.s
arnis-3243b349208c302c.addr2line-bea85df8985bb2f0.addr2line.257eabc222133535-cgu.0.rcgu.o.rcgu.s
arnis-3243b349208c302c.adler-7edbe936f6124018.adler.c05167120aaaa11-cgu.0.rcgu.o.rcgu.s
arnis-3243b349208c302c.ahash-5f4e9db20a685a8b.ahash.9ea151b83c359a1d-cgu.0.rcgu.o.rcgu.s
...
arnis-3243b349208c302c.console-c85db5ed6c6839da.console.b89a0426d30cb582-cgu.6.rcgu.o.rcgu.s
arnis-3243b349208c302c.console-c85db5ed6c6839da.console.b89a0426d30cb582-cgu.7.rcgu.o.rcgu.s
arnis-3243b349208c302c.core-1e6496089ac34c68.core.9e3ec3a99e20741e-cgu.0.rcgu.o.rcgu.s
arnis-3243b349208c302c.crc32fast-e2cdbd16bb066f34.crc32fast.a5f7f5e1cc329c1d-cgu.0.rcgu.o.rcgu.s
arnis-3243b349208c302c.crossbeam_deque-f35b3fcb74c4667c.crossbeam_deque.a044f344000c4a51-cgu.0.rcgu.o.rcgu.s
arnis-3243b349208c302c.crossbeam_epoch-a8dd3a9032740fa4.crossbeam_epoch.e375ac55259ef9a0-cgu.0.rcgu.o.rcgu.s
...

Usually generated asm is located in a file that starts with the executable name (arnis-3243b349208c302c), contains a hash and ends with .s - here it is arnis-3243b349208c302c.8qi3mr8qju3xmfjsf34x3m992.rcgu.s, but in this case it is mostly empty, and the contents are inside of arnis-3243b349208c302c.core-1e6496089ac34c68.core.9e3ec3a99e20741e-cgu.0.rcgu.o.rcgu.s

[pacak]

and the contents are inside of arnis-3243b349208c302c.core-1e6496089ac34c68.core.9e3ec3a99e20741e-cgu.0.rcgu.o.rcgu.s

But since code will be optimized at the link time later - this might not be the final code.

Should we try to detect the presence of LTO and propose either disabling it or using --disasm?

[corneliusroemer]

I'm hitting Error: Cannot locate the path to the asm file - when switching off LTO (was "thin") this error disappears

[pacak]

--disasm is probably the best solution at the moment.