No support for lto build modes? after 1.67.1

[redbaron]

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]

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]

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

[pacak]

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

[redbaron]

yes, latest released 0.2.14

[reisnera]

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"

3. Try to do anything with cargo asm

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

[pacak]

@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]

Sure, see attached flies
output.txt
filelist.txt

[pacak]

@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]

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

[reisnera]

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]

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

[pacak]

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

[pacak]

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]

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]

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]

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]

Makes sense, thank you again!

…

On Thu, Mar 9, 2023, 8:51 AM pacak ***@***.***> wrote: 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. — Reply to this email directly, view it on GitHub <#146 (comment)>, or unsubscribe <https://github.com/notifications/unsubscribe-auth/AAM3DYII6H3VEJJRO4I33VLW3HU6FANCNFSM6AAAAAAVQXDC54> . You are receiving this because you were mentioned.Message ID: ***@***.***>