Re: [BUG] i386 relocable kernel breakes /proc/kcore debugging

Re: [BUG] i386 relocable kernel breakes /proc/kcore debugging

[Eric W. Biederman]

Maxim Levitsky <maximlevitsky@gmail.com> writes:

> Hello,
>
> Today I noticed that gdb gets confused when I try to load a vmlinux image.
> gdb 'thinks' that all kernel symbols are below 0x80000000 , while they are at 
> 0xC000....
>
> Turning CONFIG_RELOCATABLE off fixes that, so I assume that is the reason for 
> that.
>
> I am using 2.6.23-rc1, although I don't think that older versions are better.
>
> Best regards,
> 	Maxim Levitsky

Weird.

Vivek could this be related to the problem of problematic core dumps we
were seeing earlier?

Eric


> PS: 
> This is what gdb says:

>
> (gdb) disassemble sys_open
> Dump of assembler code for function sys_open:
> 0x8026fa60 <sys_open+0>:        Cannot access memory at address 0x8026fa60
>
> While real address of sys_open is:
>
> [root@MAIN linux-2.6]# nm ./.obj/vmlinux |  grep sys_open
> .........
> c016ea60 T sys_open
>
> Strange, but gdb recordnizes the above address directly:
>
> (gdb) disassemble 0xc016ea60
> Dump of assembler code for function sys_open:
> 0xc016ea60 <sys_open+0>:        sub    $0x4,%esp
> 0xc016ea63 <sys_open+3>:        mov    0x10(%esp),%eax
> ...............

Re: [BUG] i386 relocable kernel breakes /proc/kcore debugging

[Vivek Goyal]

On Sat, Jul 28, 2007 at 04:43:43AM +0300, Maxim Levitsky wrote:
> Hello,
> 
> Today I noticed that gdb gets confused when I try to load a vmlinux image.
> gdb 'thinks' that all kernel symbols are below 0x80000000 , while they are at 
> 0xC000....
> 
> Turning CONFIG_RELOCATABLE off fixes that, so I assume that is the reason for 
> that.
> 

This is a gdb issue. I had raised it in gdb mailing list some time back.

http://sourceware.org/ml/gdb/2006-08/msg00137.html

What version of gdb you are using? I know it got fixed for gdb shipped
with RHEL5. I am not sure about what upstream version of gdb it got fixed
in.

I think Jan Kratochvil had put a patch to fix the issue. I am copying him
on the mail and he should be able to tell which version of gdb to use.

Thanks
Vivek

Re: [BUG] i386 relocable kernel breakes /proc/kcore debugging

[Jan Kratochvil]

On Mon, 30 Jul 2007 10:03:03 +0200, Vivek Goyal wrote:
> On Sat, Jul 28, 2007 at 04:43:43AM +0300, Maxim Levitsky wrote:
...
> > gdb 'thinks' that all kernel symbols are below 0x80000000 , while they are at 
> > 0xC000....
> > 
> > Turning CONFIG_RELOCATABLE off fixes that, so I assume that is the reason for 
> > that.
> 
> This is a gdb issue. I had raised it in gdb mailing list some time back.
> 
> http://sourceware.org/ml/gdb/2006-08/msg00137.html

There was the patch post:
	http://sources.redhat.com/ml/gdb/2006-08/msg00182.html

> What version of gdb you are using? I know it got fixed for gdb shipped
> with RHEL5. I am not sure about what upstream version of gdb it got fixed
> in.

It did not make it to the upstream as the patch above is an imperfect one.
It is fixed in RH gdb-6.5-5 upwards, therefore Fedora 6 + RHEL-5.
	http://cvs.fedora.redhat.com/viewcvs/*checkout*/devel/gdb/gdb-6.5-bz203661-emit-relocs.patch?root=core


Regards,
Jan

Re: [BUG] i386 relocable kernel breakes /proc/kcore debugging

[Maxim Levitsky]

On Monday 30 July 2007 11:41, Jan Kratochvil wrote:
> On Mon, 30 Jul 2007 10:03:03 +0200, Vivek Goyal wrote:
> > On Sat, Jul 28, 2007 at 04:43:43AM +0300, Maxim Levitsky wrote:
>
> ...
>
> > > gdb 'thinks' that all kernel symbols are below 0x80000000 , while they
> > > are at 0xC000....
> > >
> > > Turning CONFIG_RELOCATABLE off fixes that, so I assume that is the
> > > reason for that.
> >
> > This is a gdb issue. I had raised it in gdb mailing list some time back.
> >
> > http://sourceware.org/ml/gdb/2006-08/msg00137.html
>
> There was the patch post:
> 	http://sources.redhat.com/ml/gdb/2006-08/msg00182.html
>
> > What version of gdb you are using? I know it got fixed for gdb shipped
> > with RHEL5. I am not sure about what upstream version of gdb it got fixed
> > in.
>
> It did not make it to the upstream as the patch above is an imperfect one.
> It is fixed in RH gdb-6.5-5 upwards, therefore Fedora 6 + RHEL-5.
> 	http://cvs.fedora.redhat.com/viewcvs/*checkout*/devel/gdb/gdb-6.5-bz203661
>-emit-relocs.patch?root=core
>
>
> Regards,
> Jan

Hi,

I am using mandriva 2007 and gdb that come with it ( 6.3 I think)
I also compiled gdb 6.6, but the same issue persist.

Thanks for the info, and I will try to apply the above patch and see if helps,

Will it make into gdb?

By the way, I had another issue with /proc/kcore.
That enabling sparse memory model instead of flat causes /proc/kcore not to 
work at all. I traced that to a "FIXME" in sparcemem.

/* XXX: FIXME -- wli */
#define kern_addr_valid(kaddr)  (0)

Kconfig should contatin a warning for those who select sparcemem 
that /proc/kcore will be disabled.
or maybe this should be implemented (it is not easy since spacemem allows 
memory to be discontinous, and nobody wants to allow user to read reserved 
regions)

Except the above, /proc/kcore works fine, and it is very usefull.

Best regards,
	Maxim Levitsky

Best regards,
	Maxim Levitsky

Re: [BUG] i386 relocable kernel breakes /proc/kcore debugging

[Eric W. Biederman]

Jan Kratochvil <jan.kratochvil@redhat.com> writes:

> On Mon, 30 Jul 2007 10:03:03 +0200, Vivek Goyal wrote:
>> On Sat, Jul 28, 2007 at 04:43:43AM +0300, Maxim Levitsky wrote:
> ...
>> > gdb 'thinks' that all kernel symbols are below 0x80000000 , while they are
> at
>> > 0xC000....
>> > 
>> > Turning CONFIG_RELOCATABLE off fixes that, so I assume that is the reason
> for
>> > that.
>> 
>> This is a gdb issue. I had raised it in gdb mailing list some time back.
>> 
>> http://sourceware.org/ml/gdb/2006-08/msg00137.html
>
> There was the patch post:
> 	http://sources.redhat.com/ml/gdb/2006-08/msg00182.html
>
>> What version of gdb you are using? I know it got fixed for gdb shipped
>> with RHEL5. I am not sure about what upstream version of gdb it got fixed
>> in.
>
> It did not make it to the upstream as the patch above is an imperfect one.
> It is fixed in RH gdb-6.5-5 upwards, therefore Fedora 6 + RHEL-5.
> 	http://cvs.fedora.redhat.com/viewcvs/*checkout*/devel/gdb/gdb-6.5-bz203661-emit-relocs.patch?root=core

Has anyone looked at the filtering by ignoring SHTSYM_TAB?  The other
approach suggested?  The patch above only works for ET_EXEC because
we can safely ignore everything.

Eric