nix 0.26 can't work on ubuntu16.04

[rise0chen]

fn main() {
    println!("{:?}", nix::unistd::gethostname());
}

= note: /root/build/release/deps/libnix-fca8cee73dd370df.rlib(nix-fca8cee73dd370df.nix.9961a42b-cgu.2.rcgu.o): In function `nix::sys::memfd::memfd_create::hbef039c9926ba4f0':
          nix.9961a42b-cgu.2:(.text._ZN3nix3sys5memfd12memfd_create17hbef039c9926ba4f0E+0x5): undefined reference to `memfd_create'
          collect2: error: ld returned 1 exit status
          
  = help: some `extern` functions couldn't be found; some native libraries may need to be installed or have their path specified
  = note: use the `-l` flag to specify native libraries to link
  = note: use the `cargo:rustc-link-lib` directive to specify the native libraries to link with Cargo (see https://doc.rust-lang.org/cargo/reference/build-scripts.html#cargorustc-link-libkindname)

root@f0fca0e971de:~/rc3.1# gcc -v
Using built-in specs.
COLLECT_GCC=gcc
COLLECT_LTO_WRAPPER=/usr/lib/gcc/x86_64-linux-gnu/5/lto-wrapper
Target: x86_64-linux-gnu
Configured with: ../src/configure -v --with-pkgversion='Ubuntu 5.4.0-6ubuntu1~16.04.12' --with-bugurl=file:///usr/share/doc/gcc-5/README.Bugs --enable-languages=c,ada,c++,java,go,d,fortran,objc,obj-c++ --prefix=/usr --program-suffix=-5 --enable-shared --enable-linker-build-id --libexecdir=/usr/lib --without-included-gettext --enable-threads=posix --libdir=/usr/lib --enable-nls --with-sysroot=/ --enable-clocale=gnu --enable-libstdcxx-debug --enable-libstdcxx-time=yes --with-default-libstdcxx-abi=new --enable-gnu-unique-object --disable-vtable-verify --enable-libmpx --enable-plugin --with-system-zlib --disable-browser-plugin --enable-java-awt=gtk --enable-gtk-cairo --with-java-home=/usr/lib/jvm/java-1.5.0-gcj-5-amd64/jre --enable-java-home --with-jvm-root-dir=/usr/lib/jvm/java-1.5.0-gcj-5-amd64 --with-jvm-jar-dir=/usr/lib/jvm-exports/java-1.5.0-gcj-5-amd64 --with-arch-directory=amd64 --with-ecj-jar=/usr/share/java/eclipse-ecj.jar --enable-objc-gc --enable-multiarch --disable-werror --with-arch-32=i686 --with-abi=m64 --with-multilib-list=m32,m64,mx32 --enable-multilib --with-tune=generic --enable-checking=release --build=x86_64-linux-gnu --host=x86_64-linux-gnu --target=x86_64-linux-gnu
Thread model: posix
gcc version 5.4.0 20160609 (Ubuntu 5.4.0-6ubuntu1~16.04.12) 

[asomers]

According to the online man pages, that function should be available in Ubuntu 16.04. Could you please do objdump -T /lib/x86_64-linux-gnu/libc.so.6 | grep memfd and paste the results?
https://manpages.ubuntu.com/manpages/xenial/man2/memfd_create.2.html

[rise0chen]

root@f0fca0e971de:~/rc3.1# objdump -T /lib/x86_64-linux-gnu/libc.so.6 | grep memfd
root@f0fca0e971de:~/rc3.1# 

It is empty.
You can test it in docker image. https://hub.docker.com/_/ubuntu

[rise0chen]

The problem is caused by this commit cf15c2b

[asomers]

Even if memfd_create isn't included in your libc, I don't understand why the compile would fail. Normally the Rust linker eliminates unused code, so it's no problem if a symbol like memfd_create is undefined, if you don't use it. Are you using any weird compiler settings? And what version of Rust are you using anyway?

[rise0chen]

You can test this code in ubuntu:16.04 with docker.

rustc 1.65.0 (897e37553 2022-11-02)

[rise0chen]

I have updated to the latest stable rust. It also can't work.
stable-x86_64-unknown-linux-gnu updated - rustc 1.67.1 (d5a82bbd2 2023-02-07) (from rustc 1.65.0 (897e37553 2022-11-02))

[jszwedko]

We are seeing this as well for https://github.com/vectordotdev/vector when building on CentOS 7 which has:

$ ldd --version ldd
ldd (GNU libc) 2.17
Copyright (C) 2012 Free Software Foundation, Inc.
This is free software; see the source for copying conditions.  There is NO
warranty; not even for MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.
Written by Roland McGrath and Ulrich Drepper.

We build on CentOS 7 specifically to link against an older libc version for broader platform support.

[asomers]

Ubuntu 16.04 is EoL. Is CentOS 7?

[jszwedko]

I don't think Ubuntu 16.04 is EoL. It seems to be supported through April of 2026 (see https://ubuntu.com/about/release-cycle).

CentOS 7 appears to be supported through 2024-06-30 (see https://wiki.centos.org/About/Product).

[asomers]

But only in Expanded Security Maintenance, it seems.

Anyway, I can reproduce your problem only if I use RUSTFLAGS=-C link-dead-code. I think your linker probably has different default behavior. If you pass --as-needed to the linker, I think it will fix your problem.

[jszwedko]

Thanks for the tip! I tried --as-needed, but am still seeing the same error. For reference, we are using ld as the linker:

$ ld --version
GNU ld version 2.27-44.base.el7
Copyright (C) 2016 Free Software Foundation, Inc.
This program is free software; you may redistribute it under the terms of
the GNU General Public License version 3 or (at your option) a later version.
This program has absolutely no warranty.

To reproduce, you can checkout https://github.com/vectordotdev/vector at 2b28408eae2b3c43a9e88d701e57fc50cd25fad7 and run cargo build --no-default-features --features target-x86_64-unknown-linux-gnu.

Would it be useful for me to bisect nix down to the commit that introduces the issue? Or do you already have an idea of what the change is?