How to redirect the loader to another directory ?

How to redirect the loader to another directory ?

[robert song]

Hi, everyone.
Now I use qemu-arm to execute the target command on host.
But it should be executed as follows:
$ qemu-arm -E LD_LIBRARY_PATH=/target/usr/lib:/target/lib
/target/lib/ld-linux.so.3 /target/usr/bin/ls
Here /target/lib/ld-linux.so.3 should be specified, or else the host
one will be searched.

$ readelf -l /target/usr/bin/ls
(snip)
[Requesting program interpreter: /lib/ld-linux.so.3]
(snip)

Is there any method to redirect the loader to the directory I
specified (for exmaple, the root dir should be /target) without the
method above ?

Best Regards,
  robert

Re: How to redirect the loader to another directory ?

[Goswin von Brederlow]

robert song <robertsong.japan@gmail.com> writes:

> Hi, everyone.
> Now I use qemu-arm to execute the target command on host.
> But it should be executed as follows:
> $ qemu-arm -E LD_LIBRARY_PATH=/target/usr/lib:/target/lib
> /target/lib/ld-linux.so.3 /target/usr/bin/ls
> Here /target/lib/ld-linux.so.3 should be specified, or else the host
> one will be searched.
>
> $ readelf -l /target/usr/bin/ls
> (snip)
> [Requesting program interpreter: /lib/ld-linux.so.3]
> (snip)
>
> Is there any method to redirect the loader to the directory I
> specified (for exmaple, the root dir should be /target) without the
> method above ?
>
> Best Regards,
>   robert

chroot

MfG
        Goswin

Re: How to redirect the loader to another directory ?

[robert song]

> chroot

hi,Goswin,
it can't work.
$ sudo chroot /target/
chroot: cannot run command `/bin/bash': No such file or directory

/target/bin/bash was built by arm gcc.


Regards,
  robert

Re: How to redirect the loader to another directory ?

[Goswin von Brederlow]

robert song <robertsong.japan@gmail.com> writes:

>> chroot
>
> hi,Goswin,
> it can't work.
> $ sudo chroot /target/
> chroot: cannot run command `/bin/bash': No such file or directory
>
> /target/bin/bash was built by arm gcc.
>
>
> Regards,
>   robert

You would have to copy qemu and the required libs into the chroot and
call qemu in there or setup binfmt-misc for arm. Chroot on its own won't
work.

The other way I know would be to alter the linker script and recompile
binaries to use /target/lib/... as their dynamic loader. But that is
hardly practical.

MfG
        Goswin

Re: How to redirect the loader to another directory ?

[robert song]

Thank you very much, Goswin.

> You would have to copy qemu and the required libs into the chroot and
> call qemu in there or setup binfmt-misc for arm. Chroot on its own won't
> work.

the required libs may conflict with the target file. Now I build a
static qemu-arm.

Host> cd qemu-0.12.3
Host> ./configure --target-list=arm-linux-user --static
Host> make
Host> sudo cp arm-linux-user/qemu-arm /target/bin/qemu-arm
Host> sudo cd /target
Host> sudo chroot . /bin/qemu-arm /bin/sh
Host> /bin/qemu-arm /bin/ls

Now, it can work.
Regarding to binfmt-misc, I don't know it.

>
> The other way I know would be to alter the linker script and recompile
> binaries to use /target/lib/... as their dynamic loader. But that is
> hardly practical.
>

Well, it's not a good idea.

Best Regards,
  robert

Re: How to redirect the loader to another directory ?

[Goswin von Brederlow]

robert song <robertsong.japan@gmail.com> writes:

> Thank you very much, Goswin.
>
>> You would have to copy qemu and the required libs into the chroot and
>> call qemu in there or setup binfmt-misc for arm. Chroot on its own won't
>> work.
>
> the required libs may conflict with the target file. Now I build a
> static qemu-arm.

You can use the multiarch directory ([/usr]/lib/<triplet>/) to place
libraries into a unique location. Under debian this directory is
activated through /etc/ld.so.conf.d/<triplet>.conf provided by libc6.
But static building works too.

> Host> cd qemu-0.12.3
> Host> ./configure --target-list=arm-linux-user --static
> Host> make
> Host> sudo cp arm-linux-user/qemu-arm /target/bin/qemu-arm
> Host> sudo cd /target
> Host> sudo chroot . /bin/qemu-arm /bin/sh
> Host> /bin/qemu-arm /bin/ls
>
> Now, it can work.
> Regarding to binfmt-misc, I don't know it.

http://en.wikipedia.org/wiki/Binfmt_misc

  binfmt_misc is a capability of the Linux kernel which allows arbitrary
  executable file formats to be recognized and passed to certain user
  space applications, such as emulators and virtual machines.
  ...

Under Debian the qemu-arm package automatically registers qemu through
this so executing any arm binary will automatically invoke qemu
transparently.

MfG
        Goswin

Re: How to redirect the loader to another directory ?

[Mike Frysinger]

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On Thursday 13 May 2010 07:34:47 robert song wrote:
> Now I use qemu-arm to execute the target command on host.

these questions really should be posted to the qemu list since they have 
nothing to do with binutils
-mike

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Re: How to redirect the loader to another directory ?

[robert song]

hmm, I posted some topics in QEMU before and without any answer, the
QEMU list isn't active.
Now chroot can slove the QEMU problem.
But in the other way, I also want to know how to modify the other
application which execution loader path is different from the loader
path specified during build.
Because in embedded system, sometimes the dir will changed.

Best Regards,
  robert


On 5/20/10, Mike Frysinger <vapier@gentoo.org> wrote:
> On Thursday 13 May 2010 07:34:47 robert song wrote:
>> Now I use qemu-arm to execute the target command on host.
>
> these questions really should be posted to the qemu list since they have
> nothing to do with binutils
> -mike
>

Re: How to redirect the loader to another directory ?

[Mike Frysinger]

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On Wednesday 19 May 2010 23:53:56 robert song wrote:
> hmm, I posted some topics in QEMU before and without any answer, the
> QEMU list isn't active.
> Now chroot can slove the QEMU problem.
> But in the other way, I also want to know how to modify the other
> application which execution loader path is different from the loader
> path specified during build.
> Because in embedded system, sometimes the dir will changed.

telling qemu where to look up alternative paths and such is a qemu issue 
though, not a binutils.  you could relink all your apps with a different ldso 
path, and recompile your C library to use a different prefix, but that isnt 
dynamic like the qemu solution.
-mike

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Re: How to redirect the loader to another directory ?

[robert song]

Mike, you are correct, thank you very much.

Best Regards,
  robert


On 5/20/10, Mike Frysinger <vapier@gentoo.org> wrote:
> On Wednesday 19 May 2010 23:53:56 robert song wrote:
>> hmm, I posted some topics in QEMU before and without any answer, the
>> QEMU list isn't active.
>> Now chroot can slove the QEMU problem.
>> But in the other way, I also want to know how to modify the other
>> application which execution loader path is different from the loader
>> path specified during build.
>> Because in embedded system, sometimes the dir will changed.
>
> telling qemu where to look up alternative paths and such is a qemu issue
> though, not a binutils.  you could relink all your apps with a different
> ldso
> path, and recompile your C library to use a different prefix, but that isnt
> dynamic like the qemu solution.
> -mike
>