Specify the expected Linux version of the output binary of GCC

Question

I'm helping others doing a lab experiment of the "operating systems concepts" course. The experiment task is to compile Linux 2.6.26 and run it in QEMU.

After compiling the Linux kernel, we're told to write a smallest program to serve as the init program. The example we're presented (and we followed) is:

#include <stdio.h>

int main() {
    while (1) {
        puts("Hello!");
        sleep(2);
    }
}

The compilation command is:

root@ubuntu:/home/vmware/oslab# gcc --version
gcc (Ubuntu 4.8.4-2ubuntu1~14.04.4) 4.8.4
Copyright (C) 2013 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.

root@ubuntu:/home/vmware/oslab# gcc -static -o init hello.c

The host environment should be a freshly-installed Ubuntu 14.04.6 (i386).

The problem is, one of my fellow students followed the instruction carefully, and the init program failed to execute. I asked him for his whole initrd.img, and noticed how his init program looks different:

vmware@ubuntu:~/oslab$ file mnt/init
mnt/init: ELF 32-bit LSB  executable, Intel 80386, version 1 (GNU/Linux), statically linked, for GNU/Linux 2.6.32, BuildID[sha1]=7365ac494ef1d924c171899c169dbd3195d2d209, not stripped

To me, that's clearly not something that can run on Linux 2.6.26. With GCC 4.8 provided in the Ubuntu APT repository (trusty), how can I get GCC to output something that runs on Linux 2.6.26?

FYI: On my own testing VM (also Ubuntu 14.04.6, Linux 4.4, same latest GCC version from Ubuntu APT repo as of April 2, 2019), the compiled program shows Linux 2.6.24 in file output. Also, his binary runs perfectly well in QEMU with my freshly compiled 2.6.32.37 kernel.

It's a glibc thing, not a gcc thing: stackoverflow.com/questions/12236159/… — Shawn
@Shawn How can glibc matter when the binary is statically linked? — iBug
It's statically linked to a particular version of glibc, which in turn was configured to require a particular minimum kernel version. — Shawn
@Shawn Why is it glibc instead of binutils (as, ld etc.)? — iBug

bruno bruno · Accepted Answer · 2019-04-02T13:12:04

Specify the expected Linux version of the output binary of GCC

in your question you speak about the version of libc C but that can also concerns a lot of other libs, and may be you want also produce 32b and/or 64b executable(s).

For me the most secure way is to use pbuilder, I use it to produce BoUML debs for Ubuntu Cosmic (18.10) Bionic (18.04), Artful (17.10) Zesty (17.04) Yakkety (16.10) Xenial (16.04) Trusty (14.04) and Precise (12.04) and that in both 32b and 64b, and I do all of that from my Ubuntu Xenial 64b just doing the appropriate sequence of pbuilder commands (without any reboot to go in each Linux release)

That needs time to generate a version but because this is made in the corresponding Linux version you are sure of the result.

Specify the expected Linux version of the output binary of GCC

2 Answers