Segfault in argv::iter when linked with musl

[nikclayton-dfinity]

argv segfaults in unsafe code when compiled using musl instead of glibc.

Reproduction code

Cargo.toml:

[package]
name = "argv_musl_bug"
version = "0.1.0"
edition = "2018"

[dependencies]
argv = "0.1"

src/main.rs:

fn main() {
    for arg in argv::iter() {
        println!("{}", arg.to_string_lossy());
    }

    println!("After argument parsing, exiting");
}

Results

Works: On a Mac:

% uname -a
Darwin Niks-MBP 19.6.0 Darwin Kernel Version 19.6.0: Thu Jun 18 20:49:00 PDT 2020; root:xnu-6153.141.1~1/RELEASE_X86_64 x86_64 i386 MacBookPro15,1 Darwin

% cargo --version
cargo 1.45.1

% cargo run
[...]
After argument parsing, exiting

Works: In the official Rust docker container:

Note: Run docker from the crate's root, this will mount the crate's files at /crate in the container.

% docker run -it --mount type=bind,source=$(pwd),target=/crate rust:1.46
root% uname -a
Linux 8928eecdcc46 4.19.76-linuxkit #1 SMP Tue May 26 11:42:35 UTC 2020 x86_64 GNU/Linux

root% cd /crate

root% rm -rf target # just in case it's there from the Mac build

root% cargo run
[...]
After argument parsing, exiting

Fails: Static linking against musl

Still in the docker container from the previous step, follow the instructions at https://doc.rust-lang.org/edition-guide/rust-2018/platform-and-target-support/musl-support-for-fully-static-binaries.html to add the musl target

root% rustup target add x86_64-unknown-linux-musl
info: downloading component 'rust-std' for 'x86_64-unknown-linux-musl'
info: installing component 'rust-std' for 'x86_64-unknown-linux-musl'
info: Defaulting to 500.0 MiB unpack ram
 15.3 MiB /  15.3 MiB (100 %)   9.7 MiB/s in  1s ETA:  0s

Then try and build and run that target.

root% cargo run --target x86_64-unknown-linux-musl
   Compiling argv v0.1.2
   Compiling argv_musl_bug v0.1.0 (/crate)
    Finished dev [unoptimized + debuginfo] target(s) in 5.49s
     Running `target/x86_64-unknown-linux-musl/debug/argv_musl_bug`
Segmentation fault

Setting RUST_BACKTRACE=full doesn't work, you need to install gdb and run it under there, so:

root% apt-get update
[...]

root% apt-get install gdb
[...]

root% gdb target/x86_64-unknown-linux-musl/debug/argv_musl_bug
[...]
(gdb) run
Starting program: /crate/target/x86_64-unknown-linux-musl/debug/argv_musl_bug
warning: Error disabling address space randomization: Operation not permitted

Program received signal SIGSEGV, Segmentation fault.
0x00007f5406f1e02f in <argv::impl::Iter as core::iter::traits::iterator::Iterator>::next (
    self=0x7ffdf6ea4b48)
    at /usr/local/cargo/registry/src/github.com-1ecc6299db9ec823/argv-0.1.2/src/lib.rs:119
119	                let ptr = unsafe { *self.next };
(gdb) bt
#0  0x00007f5406f1e02f in <argv::impl::Iter as core::iter::traits::iterator::Iterator>::next (
    self=0x7ffdf6ea4b48)
    at /usr/local/cargo/registry/src/github.com-1ecc6299db9ec823/argv-0.1.2/src/lib.rs:119
#1  0x00007f5406f1de9f in <argv::Iter as core::iter::traits::iterator::Iterator>::next (
    self=0x7ffdf6ea4b48)
    at /usr/local/cargo/registry/src/github.com-1ecc6299db9ec823/argv-0.1.2/src/lib.rs:56
#2  0x00007f5406f1da83 in argv_musl_bug::main () at src/main.rs:2

This obviously affects anything that tries to use argv, including gflags.

[nikclayton-dfinity]

Based on golang/go#13492, musl appears to believe that libraries don't get access to argv/argc, and the equivalent of main() should pass the values to the library.

[nikclayton-dfinity]

https://inbox.vuxu.org/musl/20200715023432.GC14669@brightrain.aerifal.cx/ has more context.

[dtolnay]

Thanks! I published 0.1.3 with a fix.

[nikclayton-dfinity]

Thanks, that was quick. Please can you also publish a new version of gflags that bumps the argv dependency (which is currently pinned to 1.1.1).

[dtolnay]

Done.

[nikclayton-dfinity]

That is great -- thanks again.