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Re: custom kernel on lemote-3a-itx (Loongson-3A) crashes in userspace

To: Mike Frysinger <>
Subject: Re: custom kernel on lemote-3a-itx (Loongson-3A) crashes in userspace
From: Huacai Chen <>
Date: Thu, 26 Feb 2015 15:47:44 +0800
Cc: Linux MIPS Mailing List <>
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Please try the toolchain here:

On Fri, Feb 20, 2015 at 3:46 AM, Mike Frysinger <> wrote:
> i've got a lemote desktop with a quad core Loongson-3A in it:
> i'm trying to build my own kernel for it, but userspace just crashes on me :(.
> the current kernel is a precompiled one from lemote themselves, and things are
> compiling/running fine with it.  but it's a bit stale and missing features i
> want (like namespaces & seccomp).
> $ uname -a
> Linux lemote 3.5.0-9.lemote #1465 SMP PREEMPT Mon Aug 26 14:23:38 CST 2013 
> mips64 ICT Loongson-3A V0.5 FPU V0.1 lemote-3a-itx-a1101 GNU/Linux
> the userland is Gentoo.  it's an o32/n32/n64 multilib with n32 as the default.
> most (if not all) of userland has been built with gcc-4.8.2 using
> "-O2 -march=mips64 -mplt -pipe".
> $ file /bin/bash
> /bin/bash: ELF 32-bit LSB executable, MIPS, N32 MIPS64 version 1 (SYSV), 
> dynamically linked, interpreter /lib32/, for GNU/Linux 2.6.16, stripped
> $ /lib/
> GNU C Library (Gentoo 2.19-r1 p3) stable release version 2.19, by Roland 
> McGrath et al.
> Copyright (C) 2014 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
> Compiled by GNU CC version 4.8.2.
> Compiled on a Linux 3.14.0 system on 2014-09-09.
> Available extensions:
>         C stubs add-on version 2.1.2
>         crypt add-on version 2.1 by Michael Glad and others
>         GNU Libidn by Simon Josefsson
>         Native POSIX Threads Library by Ulrich Drepper et al
>         BIND-8.2.3-T5B
> For bug reporting instructions, please see:
> <>.
> i first tried lemote's sources, which i grabbed their git tree from
>  i started at the same git tag (3.5.0-9.lemote) and used the
> same .config as their precompiled kernel.  once it booted, most userland progs
> would crash.  some would survive (like simple ones), but most would crash.
> i moved up to vanilla linux-3.18, starting with the same config, but got the
> same behavior.
> i tried booting with the nofpu command line, but that didn't help.  i also
> tried manually setting cpu_has_fpu to 0 in
> arch/mips/include/asm/mach-loongson/cpu-feature-overrides.h, but that didn't
> help.
> i tried gcc-4.7.4, gcc-4.8.4, and gcc-4.9.2, but none of that helped.
> i enabled the debugging in arch/mips/mm/fault.c, and you can see the attached
> dmesg with some of the example crashes.  when i looked at proc maps from other
> binaries, it looks like those crashing addresses are close to real ones, but
> slightly off (like a byte shift?).  i'm just guessing since i'm not actually
> looking at the crashing app itself ... just assuming the maps are largely 
> stable
> (since they seem to be in other ones).
> i tried to use strace/gdb to narrow things down, but those both crash early, 
> so
> couldn't get anywhere :).
> any pointers ?
> -mike

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