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Re: recent SIGBUS/SIGSEGV mips kernel bug

To: David Daney <ddaney@caviumnetworks.com>
Subject: Re: recent SIGBUS/SIGSEGV mips kernel bug
From: Camm Maguire <camm@maguirefamily.org>
Date: Thu, 21 Oct 2010 15:07:57 -0400
Cc: debian-mips@lists.debian.org, Frederick Isaac <freddyisaac@gmail.com>, gcl-devel@gnu.org, linux-mips <linux-mips@linux-mips.org>
In-reply-to: <4CC0787C.2040902@caviumnetworks.com> (David Daney's message of "Thu\, 21 Oct 2010 10\:29\:32 -0700")
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Greetings!

David Daney <ddaney@caviumnetworks.com> writes:

> On 10/21/2010 09:19 AM, David Daney wrote:
>> On 10/20/2010 02:31 PM, Camm Maguire wrote:
>>> Greetings!
>>>
>>> Does this suffice?
>>>
>>> (sid)camm@gabrielli:~/maxima-5.22.1/tests$ uname -a
>>> Linux gabrielli 2.6.35.4-dsa-octeon #1 SMP Fri Sep 17 21:15:34 UTC
>>> 2010 mips64 GNU/Linux
>>> (sid)camm@gabrielli:~/maxima-5.22.1/tests$ cat /proc/cpuinfo
>>> system type : CUST_WSX16 (CN3860p3.X-500-EXP)
>>> processor : 0
>>> cpu model : Cavium Octeon V0.3
>> [...]
>>
>> Hah! I have those things piled up all around me.
>>
>> No guarantees, but I will try to reproduce it. If I can reproduce it, it
>> should be easy to fix.
>>
>
> Definitely a kernel bug.  Consider this program:
>
> ------------8<--------sigbus.c-------
> #include <stdio.h>
> #include <stdlib.h>
> #include <unistd.h>
>
> #include <sys/mman.h>
>
> int main(int argc, char *argv[])
> {
>   int pgsize;
>   float *p1;
>   float *p2;
>   int r;
>
>   pgsize = getpagesize();
>
>   p1 = mmap(NULL, pgsize, PROT_READ | PROT_WRITE,
>           MAP_PRIVATE | MAP_ANONYMOUS, -1, 0);
>
>   if (p1 == MAP_FAILED) {
>     perror("mmap p1 failed");
>     exit(1);
>   }
>
>   p2 = mmap(NULL, pgsize, PROT_READ | PROT_WRITE,
>           MAP_PRIVATE | MAP_ANONYMOUS, -1, 0);
>
>   if (p2 == MAP_FAILED) {
>     perror("mmap p2 failed");
>     exit(1);
>   }
>
>   *p1 = 2.5;
>   *p2 = 3.5;
>
>   r = mprotect(p1, pgsize, PROT_READ);
>   if (r) {
>     perror("mprotect p1 failed");
>     exit(1);
>   }
>
>   r = mprotect(p2, pgsize, PROT_READ);
>   if (r) {
>     perror("mprotect p2 failed");
>     exit(1);
>   }
>
>   *p2 = *p1;
>
>   asm volatile("" ::: "memory");
>
>   puts("All done!");
>
>   exit(0);
> }
> ------------8<-----------------------
>
> $ mips64-octeon-linux-gnu-gcc -Wall -mhard-float -march=mips64 -O3 -o 
> sigbus sigbus.c
> $ mips64-octeon-linux-gnu-objdump -d sigbus > sigbus.dis
>
> The float copy '*p2 = *p1;' dissassembles as:
>
>    120000b30: c6400000        lwc1    $f0,0(s2)
>    120000b34: e6000000        swc1    $f0,0(s0)
>
> When run on an FPU-less system I get:
>
> ~ # ./sigbus
> Bus error
>
> When run on my x86_64 workstation:
>
> $ ./sigbus
> Segmentation fault (core dumped)
>
> I will fix this kernel bug.
>

Great!  Thanks!  If you have time to drop a quick note when done, that
would be awesome.

Separately, do you know where I can find pre-built gdb binaries for
mips64, i.e. to debug -mabi=64?  I'm assuming that is the 'official
one' going foward.  (I have an account on the gcc compile farm.)

Thanks so much!

> David Daney
>
>
>
>

-- 
Camm Maguire                                        camm@maguirefamily.org
==========================================================================
"The earth is but one country, and mankind its citizens."  --  Baha'u'llah

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