Graphical desktop, l4con, mag

[Leslie Zhai]

Hi Jean,

Thanks for your help!


在 2017年06月03日 04:56, Jean Wolter 写道:
> Hello Leslie,
>
> On 02/06/17 11:33, Jean Wolter wrote:
>> I replaced my "ned" binary with yours and the system boots up fine.
>>
>> Now I wonder how I could reproduce your problem. It looks like I
>>
>>   * either need all binaries or
>>   * need to build them the same way you are building them. I used a
>>     fresh checkout from the svn repositories and use  gcc version
>>     4.9.2 (Debian 4.9.2-10) to build the components.
>>
>
> Since I neither have your binaries nor know how you build them
I follow the http://os.inf.tu-dresden.de/fiasco/build.html and 
http://l4re.org/build.html
and my environment is Fedora 24, gcc 6.3.1, qemu 2.6.2 and clang-5.0svn.
hello example is able to work :)


> I thought about how you could diagnose the problem further. To 
> demonstrate how to do this I intentionally added a null pointer 
> dereference to ned and would like to discuss how I would diagnose this.
>
>     --- ned/server/src/main.cc    (revision 72)
>     +++ ned/server/src/main.cc    (working copy)
>     @@ -35,6 +35,8 @@
>        Dbg::set_level(Dbg::Warn);
>        info.printf("Hello from Ned\n");
>
>     +  *(int *)0 = 0;
>     +
>        boot_info.printf("cmdline: ");
>        for (int i = 0; i < argc; ++i)
>          boot_info.cprintf("%s ", argv[i]);
>
> 1. Add -serial_esc -wait to kernel options in conf/modules.list
>
>     --- modules.list    (revision 72)
>     +++ modules.list    (working copy)
>     @@ -80,6 +80,7 @@
>      module libuc_c.so
>
>      entry framebuffer-example-x86
>     +kernel fiasco -serial_esc -wait
>      roottask moe rom/x86-fb.cfg
>      module x86-fb.cfg
>      module l4re
>
> If you boot this the kernel will enter the kernel debugger before 
> doing anything else. Enter the following commands:
>
>   * P+  /* show every pagefault before forwarding it to the pager */
>   * Prx0<space>100<space>  /* restrict pagefault logging to pagefaults
>     between [0-100] */.
>   * g  /* go */
>
> The kernel should stop when the access to 0x18 happens, then you can 
> enter the kernel debugger using 'i' and can check who is responsible 
> and maybe get a correct instruction pointer. If I do this here it 
> looks like follows (I added -serial stdio to the qemu options):
>
> qemu-system-x86_64 -kernel 
> /home/jw5/build/tmp/l4re/bin/amd64_K8/bootstrap -append "bootstrap 
> -modaddr 0x01100000" -serial stdio -initrd 
> "/home/jw5/build/tmp/fiasco//fiasco -serial_esc 
> -wait,/home/jw5/build/tmp/l4re/bin/amd64_K8/l4f/sigma0 
> ,/home/jw5/build/tmp/l4re/bin/amd64_K8/l4f/moe 
> rom/x86-fb.cfg,/home/jw5/src/l4resvn/src/l4/conf/examples//x86-fb.cfg 
> ,/home/jw5/build/tmp/l4re/bin/amd64_K8/l4f/l4re 
> ,/home/jw5/build/tmp/l4re/bin/amd64_K8/l4f/ned 
> ,/home/jw5/build/tmp/l4re/bin/amd64_K8/l4f/io 
> ,/home/jw5/src/l4resvn/src/l4/pkg/io/io/config//x86-legacy.devs 
> ,/home/jw5/src/l4resvn/src/l4/conf/examples//x86-fb.io 
> ,/home/jw5/build/tmp/l4re/bin/amd64_K8/l4f/fb-drv 
> ,/home/jw5/build/tmp/l4re/bin/amd64_K8/l4f/mag 
> ,/home/jw5/build/tmp/l4re/bin/amd64_K8/l4f/ex_fb_spectrum_cc "
> ...
> Freeing init code/data: 49152 bytes (12 pages)
>
> Calibrating timer loop... done.
>
> ---------------------------------------------------------------------
>     CPU 0 [fffffffff003df99]: Wait
> jdb: P+
when I input p+ then pressed Enter, but jdb did not print out "PF 
logging enabled" to me https://pbs.twimg.com/media/DBcu1DUUwAAkiDl.png


> PF logging enabled
> jdb: Pr restrict to addr in [0-100]     /* pressed 
> Prx0<space>100<space> */
> PF logging enabled, restricted to 0000000000000000 <= pfa <= 
> 0000000000000100
> jdb: g     /* g does no show up in output */
but input g then pressed Enter will continue to go 
https://pbs.twimg.com/media/DBc0XlWUAAAmgSN.png sorry I am not familiar 
with jdb, but have some experience with gdb.


> ...
> MOE: cmdline: /home/jw5/build/tmp/l4re/bin/amd64_K8/l4f/moe rom/x86-fb.cfg
> MOE: Starting: rom/ned rom/x86-fb.cfg
> MOE: loading 'rom/ned'
> pf:  0022 pfa=0000000000000000 ip=00000000010038a2 (w-) 
> spc=0xffffffff807c3dd8
> /* press i */
> ---------------------------------------------------------------------
>     CPU 0 [fffffffff0062116]: LOG
> jdb:
>
> Now you can use the kernel debugger to inspect the current state of 
> the system. Here I simply use addr2line to find the error:
so I failed to debug the on purpose null ptr dereference issue *(int *)0 
= 0; in your patch via jdb.


>     addr2line -p -i -e bin/amd64_K8/l4f/ned -a 10038a2
>     0x00000000010038a2:
>     /home/jw5/src/l4resvn/src/l4/pkg/l4re-core/ned/server/src/main.cc:38
>      (inlined by)
>     /home/jw5/src/l4resvn/src/l4/pkg/l4re-core/ned/server/src/main.cc:77
>
>
> Line 38 is the line with the null pointer dereference.
>
> I hope this helps,
> Jean
>
>
>

-- 
Regards,
Leslie Zhai - a LLVM hacker https://reviews.llvm.org/p/xiangzhai/

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