rust-analyzer fails to expand proc-macro when mold linker is used

[pacak]

I'm using stable rustc, most recent rust-analyzer and static build of mold as of a week ago or so.

config.toml:

[build]
rustflags = "-C target-feature=+fma,+avx2"

[target.x86_64-unknown-linux-gnu]
linker = "/usr/bin/clang"
rustflags = ["-Clink-arg=-fuse-ld=/path/to/mold"]

When deriving via proc macro is used (here serde, but any other proc macro fails

use serde::Serialize;

#[derive(Debug, Serialize)]
pub enum Distance {
    Long,
    Short,
}

rust analyzer fails to expand the macro with an error like this:
(this error is most likely about some different proc macro)

proc-macro /path/target/debug/deps/libtracing_attributes-7c1265016b85e087.so failed to find the given version. Reason: Invalid ELF section header offset/size/alignment                                                       
Failed to find proc macros. Error: ExpansionError(                                                                                                                                                                                            
    "Cannot create expander for /path/target/debug/deps/libtracing_attributes-7c1265016b85e087.so: Custom { kind: InvalidData, error: Error(\"Invalid ELF section header offset/size/alignment\") }",
)

You can invoke rust analyzer like this

rust-analyzer analysis-stats . 

The same code works as expected when compiled in a usual way

[rui314]

I created a new Rust project on my machine, copy-n-paste your code and build it with mold. I also built rust-analyzer with mold. But I couldn't reproduce the issue -- rust-analyzer analysis-stats . works with and without mold. Is there more hidden conditions to reproduce the issue? Did you observe the same issue when building programs that are publicly available? (If so, I can try that too)

[pacak]

I saw (and still see) this problem only when running rust-analyzer on a project that uses mold. The same code links and runs fine. I guess I'll try to upgrade all the things first and if it's still not working - to make a better reproduction, maybe a docker imagine or something like that.

…

On Wed, Jul 7, 2021, 21:55 Rui Ueyama ***@***.***> wrote: I created a new Rust project on my machine, copy-n-paste your code and build it with mold. I also built rust-analyzer with mold. But I couldn't reproduce the issue -- rust-analyzer analysis-stats . works with and without mold. Is there more hidden conditions to reproduce the issue? Did you observe the same issue when building programs that are publicly available? (If so, I can try that too) — You are receiving this because you authored the thread. Reply to this email directly, view it on GitHub <#80 (comment)>, or unsubscribe <https://github.com/notifications/unsubscribe-auth/AAAQFI4HMEDBS2ZI4GXKAY3TWRMGHANCNFSM473SW6OQ> .

[rui314]

Yeah, it's great if you can reproduce the issue in a Docker.

[nehaljwani]

Steps to reproduce the problem:

# cat Cargo.toml 
[package]
name = "dummy"
version = "0.0.0"
edition = "2018"

[dependencies]
object = { version = "0.25.3", default-features = false, features = ["read_core", "elf"] }
memmap2 = "0.3.0"

# cat src/main.rs 
use std::env;

use std::fs::File;
use memmap2::MmapOptions;
use object::read::{File as BinaryFile};

fn main() {
    let args: Vec<String> = env::args().collect();
    let file = File::open(&args[1]).expect(":'(\t");
    let mmap = unsafe { MmapOptions::new().map(&file).expect(":'(\t") };
    BinaryFile::parse(&*mmap).expect(":(\t");
}

# ~/.cargo/bin/cargo build
    Finished dev [unoptimized + debuginfo] target(s) in 0.02s

# echo 'void foo() {};' | clang -xc - -fuse-ld=/root/mold/mold -shared -o libfoo.so

# ./target/debug/dummy /lib/x86_64-linux-gnu/libc.so.6
# echo $?
0

# ./target/debug/dummy $(readlink -f libfoo.so)
thread 'main' panicked at ':(	: Error("Invalid ELF section header offset/size/alignment")', src/main.rs:11:31
note: run with `RUST_BACKTRACE=1` environment variable to display a backtrace

# echo $?
101

[nehaljwani]

Update: If I add the "unaligned" feature to the object dependency, then it works. This is not present at https://github.com/rust-analyzer/rust-analyzer/search?l=TOML&q=object . I don't know why it works though.

[pacak]

Let me know if an example above is working for you. If not - I'll try to make something in docker.

[rui314]

@nehaljwani Thank you very much for the detailed instructions on how to reproduce the issue! With that, I could easily reproduce it and found the cause of the issue. The bug was a little bit surprising -- we haven't aligned the section header to a 4 or 8 byte boundaries until now. x86 isn't sensitive to data alignments, so it happened to work. The problem has been fixed.