From mboxrd@z Thu Jan  1 00:00:00 1970
From: ludo@gnu.org (Ludovic =?utf-8?Q?Court=C3=A8s?=)
Subject: Re: glibc 2.26 refuses to run on CentOS 6.8
Date: Fri, 23 Feb 2018 23:26:12 +0100
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In-Reply-To: <87eflgstqt.fsf@mdc-berlin.de> (Ricardo Wurmus's message of "Mon,
	19 Feb 2018 19:46:02 +0100")
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To: Ricardo Wurmus <ricardo.wurmus@mdc-berlin.de>
Cc: guix-devel@gnu.org, 30537@debbugs.gnu.org

Hello,

Ricardo Wurmus <ricardo.wurmus@mdc-berlin.de> skribis:

> I have a bad day.  After the upgrade to glibc 2.26 none of the
> Guix-installed software runs on the HPC cluster running CentOS 6.8.

Bah.  :-(

> The glibc 2.26 expects a minimum kernel version of 3.x on x86_64, but
> CentOS 6.8 only comes with a heavily patched 2.6.32.

It=E2=80=99s annoying, but we can surely apply the patch you sent (though r=
ather
by passing =E2=80=98--enable-kernel=E2=80=99 if possible, as Danny suggeste=
d.)


personality(2) has a knob to change the kernel version reported by
uname(2) to 2.6.  Here it=E2=80=99s a case where we=E2=80=99d need the reve=
rse:
reporting 3.2 instead of 2.6.  That doesn=E2=80=99t seem to exist.

Looking for other hacks (or kludges), I found the kernel module below at
<https://www.linuxquestions.org/questions/linux-general-1/uname-hack-module=
s-in-kernel-2-6-a-172167/>,
which could be adjusted to report a different kernel version:

--8<---------------cut here---------------start------------->8---
#include <linux/kernel.h>
#include <linux/module.h>
#include <linux/utsname.h>

#ifndef UNAME_DUMB_STEPPING
#define UNAME_DUMB_STEPPING '5';
#endif

MODULE_AUTHOR("The one who invented the uname hack");
MODULE_DESCRIPTION("Changes the uname output");
MODULE_LICENSE("GPL");

static int uname_hack_init() {
	save =3D system_utsname.machine[1];
	system_utsname.machine[1] =3D UNAME_DUMB_STEPPING;
	return 0;
}

static void uname_hack_cleanup() {
	system_utsname.machine[1] =3D save;
}

module_init(uname_hack_init);
module_exit(uname_hack_cleanup);
--8<---------------cut here---------------end--------------->8---

Another option would be to ptrace processes, handle the first =E2=80=98unam=
e=E2=80=99
call, and then PTRACE_DETACH.  Ugly.

Ludo=E2=80=99.