rustc "unexpected panic"; no /proc/self/exe inside a debootstrap chroot

Opened by Nigel Tao at 2022-05-25 07:10:38

I installed rustc in a Debian chroot, as per https://wiki.debian.org/Debootstrap

sudo debootstrap testing /debian-testing-chroot https://deb.debian.org/debian/

Inside that chroot, rustc crashes.

# rustc hello.rs
Can't read /proc/cpuinfo: No such file or directory
error: internal compiler error: unexpected panic

note: the compiler unexpectedly panicked. this is a bug.

note: we would appreciate a bug report: https://github.com/rust-lang/rust/blob/master/CONTRIBUTING.md#bug-reports

note: rustc 1.21.0 running on x86_64-unknown-linux-gnu

thread 'rustc' panicked at 'failed to get current_exe: no /proc/self/exe available. Is /proc mounted?', src/librustc/session/filesearch.rs:169:22
note: Run with `RUST_BACKTRACE=1` for a backtrace.

# ls /proc
#

Sure, I can tinker with my chroot configuration to flesh out /proc, but as rustc's output said, "the compiler unexpectedly panicked. this is a bug".

RUST_BACKTRACE=1 doesn't give much information.

# RUST_BACKTRACE=1 rustc hello.rs
Can't read /proc/cpuinfo: No such file or directory
error: internal compiler error: unexpected panic

note: the compiler unexpectedly panicked. this is a bug.

note: we would appreciate a bug report: https://github.com/rust-lang/rust/blob/master/CONTRIBUTING.md#bug-reports

note: rustc 1.21.0 running on x86_64-unknown-linux-gnu

note: run with `RUST_BACKTRACE=1` for a backtrace

thread 'rustc' panicked at 'failed to get current_exe: no /proc/self/exe available. Is /proc mounted?', src/librustc/session/filesearch.rs:169:22
stack backtrace:
   0: <unknown>
   1: <unknown>
   2: <unknown>
   3: <unknown>
   4: <unknown>
   5: <unknown>
   6: <unknown>
   7: <unknown>
   8: <unknown>
   9: <unknown>
  10: <unknown>
  11: <unknown>
  12: <unknown>
  13: <unknown>
  14: <unknown>
  15: <unknown>

Nigel Tao at 2017-11-19 02:19:02

Getting the same when building cryptography for python.
```
rustc' panicked at 'failed to get current_exe: no /proc/self/exe available. Is /proc mounted
```
Source at this project: https://github.com/guysoft/MagicMirrorOS
Guy Sheffer at 2021-04-08 15:46:12
I'm having the same issue when compiling a simple rust program inside a sandbox. The error I get is:
```
error: Unable to proceed. Could not locate working directory.: no /proc/self/exe available. Is /proc mounted?
```
The simple rust program I'm trying to compile is:
```
fn main() { 
    println!("Hey there!"); 
}
```
Is there any workaround to avoid mounting proc inside the sandbox?

Source of the sandbox: https://github.com/alerighi/tabox
filippoSelvatici at 2021-09-30 09:03:47
We need /proc/self/exe to implement std::env::current_exe() which rustc uses to locate the sysroot.
bjorn3 at 2022-05-15 17:26:43
@bjorn3 that is going to be a problem, because some sandboxes (such as Sandstorm) deliberately avoid mounting /proc to reduce attack surface. I think rustc should have a compiled-in fallback if /proc is not mounted.
Demi Marie Obenour at 2022-05-25 04:01:27
You can pass --sysroot to manually specify the sysroot location. Rustc can't have a builtin fallback as there is no stamdard location to install it. Some put it in /usr, others in /usr/local amd rustup puts it in ~/.rustup/toolchains/<toolchain name>.
bjorn3 at 2022-05-25 06:49:02
Also note that libc itself needs /proc to be mounted for certain things. For example musl libc needs it for ttyname and both glibc and musl need it for fchmodat. In both cases to pass an fd to a syscall expecting a path using /proc/self/fd.
bjorn3 at 2022-05-25 07:10:38