pacak/cargo-show-asm

No support for lto build modes? after 1.67.1

redbaron opened this issue · 17 comments

redbaron commented

When I enable lto = "thin" in the release profile cargo asm stops showing assembly output for my binary:

warning: ignoring emit path because multiple .s files were produced
Error: Cannot locate the path to the asm file
pacak commented

Is it the most recent version? What platform? Do you have your project available somewhere or can you make a minimal example? Works for me...

redbaron commented

I am on latest 1.67.1 stable on ARM64. I'll try to prepare minimal reproducer

pacak commented

Is it the most recent version of cargo-show-asm?

redbaron commented

yes, latest released 0.2.14

reisnera commented

This is happening to me in linux (well, WSL). Latest rust, latest cargo-show-asm. Minimal reproducible example:

  1. Make a new empty project with cargo new
  2. Add to Cargo.toml:
[profile.release]
lto = "thin"
  1. Try to do anything with cargo asm

Edit: I should specify, I got the same error as @redbaron

  • 👀1
pacak commented

@reisnera this works for me fine on linux. Can you nuke target (cargo clean), run it with cargo asm -vvv and attach the full output here? Also a list of all the files in target would be great.

reisnera commented

Sure, see attached flies
output.txt
filelist.txt

pacak commented

@reisnera

  • Is it working fine for other rust projects?
  • Do you have incremental compilation enabled by any chance?
  • Can you try clearing CARGO_INCREMENTAL env variable if you have one?
pacak commented

This seems to be related rust-lang/cargo#7765

reisnera commented

Hey @pacak thanks for the reply. If I don't try to use lto in this new/empty project it works just fine. I tried disabling incremental compilation by setting CARGO_INCREMENTAL=0 and it still doesn't work (I do not have this set to anything normally, which I assume means incremental compilation is enabled by default).

pacak commented

Managed to reproduce it locally by upgrading rustc to 1.67.1, was working fine with 1.66.0. Will poke around.

pacak commented

rust-lang/rust#103610 - caused by this it seems

pacak commented

A workaround is to pass -C lto=no or -C lto=fat, need to figure out how to detect if it failed due to lto and try again without it automagically...

pacak commented

need to figure out how to detect if it failed due to lto and try again without it automagically...

Actually cargo-show-asm only looks at what rustc generates so lto settings should not affect the results. Always using -Clto=no works. Released 0.2.15.

reisnera commented

Awesome thanks! Great tool btw!

Question for my learning: wouldn't lto affect the generated asm as it would affect inlining and subsequent optimizations?

pacak commented

It might affect the final result in some cases - cross crate inlining perhaps, it should still produce the same results for a single create code because of -Ccodegen-units=1. Situation can probably be improved but for now I'm just fixing a regression.

reisnera commented