[BUG] Llvm-plugins failed when build the same nightly rustc to stage2 rustc

[llooFlashooll]

Hi guys, I try to use these commands to build the rustc compiler from the source and link its stage2. I just modified the nightly config in the config.toml, and found it cannot -Z llvm-plugins= load the passes. However, I can do it successfully in the same version of the rustup install nightly-x compiler.

cp config.example.toml config.toml
python3 x.py build --stage 2 -j 8

Here is the rustc --version --verbose message of both nightly and stage2 versions:

rustc 1.76.0-nightly (3f28fe133 2023-12-18)
binary: rustc
commit-hash: 3f28fe133475ec5faf3413b556bf3cfb0d51336c
commit-date: 2023-12-18
host: x86_64-unknown-linux-gnu
release: 1.76.0-nightly
LLVM version: 17.0.6

Here is the error message of the stage2 compiler. The nightly-installed one can successfully execute.

RUSTFLAGS="-Z unstable-options -Z llvm-plugins=../../afl-llvm-pass.so" cargo build

error: failed to run LLVM passes: Failed to load pass plugin../../afl-llvm-pass.so <- It can be any .so file.

What is the correct config.example.toml setting and the procedure?

[jieyouxu]

rustc 1.76.0-nightly (3f28fe1 2023-12-18)

Does this repro on a rustc built on latest master? And what rustc is the cargo build actually running?

[llooFlashooll]

No. I build from scratch of the nightly (3f28fe1) compiler by git reset to the commit hash.
cargo build applies to any Rust program, when you try to -Z llvm-plugins=.

This bug can be reproduced I think, and looks strange. I don't know how to address it.

[jieyouxu]

That commit is ancient. Like, more than a year ago. I ask what rustc cargo build is running because you could be running idk stable rustc and not whatever rustc you built. What does cargo -vV say?

[llooFlashooll]

cargo build -> I build the rust-url project. But actually this case applies to HelloWorld Rust program.
-Z llvm-plugins= -> I want to load my own afl-fuzz.so to fuzz the rust-url project.

I don't think the commit is old. Just close to a year. Besides, for example, a lot of projects rely on llvm. Usually we cannot update to too recent llvm version. This rustc supports llvm-17, which is already quite new. The rustc is also quite new. (We all know that a project undergoes one year is so common.)

Here is cargo -vV.

cargo 1.85.0-nightly (4c39aaff6 2024-11-25)
release: 1.85.0-nightly
commit-hash: 4c39aaff66862cc0da52fe529aa1990bb8bb9a22
commit-date: 2024-11-25
host: x86_64-unknown-linux-gnu
libgit2: 1.8.1 (sys:0.19.0 vendored)
libcurl: 8.9.0-DEV (sys:0.4.74+curl-8.9.0 vendored ssl:OpenSSL/1.1.1w)
ssl: OpenSSL 1.1.1w  11 Sep 2023
os: Ubuntu 22.4.0 (jammy) [64-bit]

[llooFlashooll]

Another way is that maybe I want to know, how to build a rustc compiler from scratch as the same as nightly-installed compiler?
There are so many configurations in the config.toml.example.

[jieyouxu]

You are not using the rustc you built. This cargo build invocation is using the nightly rustc shipped with the nightly 2024-11-25 toolchain. Did you link the stage2 rustc via https://rustc-dev-guide.rust-lang.org/building/how-to-build-and-run.html?highlight=rustup%20link#creating-a-rustup-toolchain? Then, I would've expected your cargo invocation to look sth like cargo +stage2 build.

[jieyouxu]

cc @nikic @ZuseZ4 since you may have any ideas (I don't test this configuration at all)... Do you happen to know if this configuration is possible?

cc #127577.

[ZuseZ4]

I can cinfirm that I used -Z llvm-plugins just a month ago successfully with Enzyme on a self-build rustc. I can share more details later today.

I did use the configure command mentioned here:
https://enzyme.mit.edu/index.fcgi/rust/installation.html#build-instructions

I am pretty sure llvm.enable_plugins isn't set to true by default.

[jieyouxu]

Oh right. You may need to explicitly build LLVM and also configure config.toml with

[llvm]
plugins = true

But I'm not 100% sure, because I've never used this myself.

[llooFlashooll]

Sorry, I tried the instructions you provided, and still triggered this bug. @jieyouxu. Let me try the instructions by @ZuseZ4.

[llooFlashooll]

Hi @ZuseZ4 , the configuration setting works, and it fixes the issue. Thanks.