Re: BINFMT_FLAT: reloc outside program

Hi Waldemar,

On 05/04/16 20:49, Waldemar Brodkorb wrote:
> Hi uClinux/elf2flt devs,
>
> How can I debug an issue with the following error while
> executing:
> ~ # ./hello
> BINFMT_FLAT: reloc outside program 0xb5890000 (0 - 0x125a4/0x8b0c),
> killing hello!
> SEGV
>
> The target is an ARM Cortex-M4 device. The error is only happening
> when libpthread from uClibc-ng is used in the binary. Non-threading
> applications are working fine. (Linuxthreads.old used)
> The problem was reported by Thomas Petazzoni from Buildroot project.
>
> On the build system I used this example code:
> http://timmurphy.org/2010/05/04/pthreads-in-c-a-minimal-working-example/
>
> $ /usr/bin/arm-openadk-uclinux-uclibceabi-gcc -o hello hello.c -lpthread
> $ /usr/bin/arm-openadk-uclinux-uclibceabi-flthdr -k hello
> $ /usr/bin/arm-openadk-uclinux-uclibceabi-flthdr -p hello
> hello
>      Magic:        bFLT
>      Rev:          4
>      Build Date:   Tue Apr  5 12:28:25 2016
>      Entry:        0x45
>      Data Start:   0x8b4c
>      Data End:     0xe384
>      BSS End:      0x125e0
>      Stack Size:   0x1000
>      Reloc Start:  0xe384
>      Reloc Count:  0x197
>      Flags:        0x11 ( Load-to-Ram Kernel-Traced-Load )
>
> On the target system:
> ~ # ./hello
> BINFMT_FLAT: Loading file: ./hello
> Mapping is 70020000, Entry point is 45, data_start is 8b4c
> Load ./hello: TEXT=70020040-70028b4c DATA=70028b50-7002e388
> BSS=7002e388-700325e4
> BINFMT_FLAT: reloc outside program 0xb5890000 (0 - 0x125a4/0x8b0c),
> killing hello!
> SEGV
>
> You can find readelf, objdump -x, objdump -D and the source of
> hello.c here:
> http://debug.openadk.org/arm-pthreads/

If you compile supplying "-v" in the elf2flt flags then it
will produce a verbose output that contains all the relocation
information. That will be helpful here. (Post it here too if
you want).


> Stracing the process does not work:
> ~ # ./strace ./hello
> BINFMT_FLAT: Loading file: ./hello
> ./strace: Can't attach to 45: No such process
> ~ # Mapping is 70560000, Entry point is 45, data_start is 8b4c
> Load ./hello: TEXT=70560040-70568b4c DATA=70568b50-7056e388
> BSS=7056e388-705725e4
> BINFMT_FLAT: reloc outside program 0xb5890000 (0 - 0x125a4/0x8b0c),
> killing hello!

strace won't help you here. The program isn't running yet, the
relocation failure is at exec time.


> gdbserver (gdb 7.11) does not compile for me as it uses fork():
>         build-gnulib-gdbserver/import/libgnu.a
> build-libiberty-gdbserver/libiberty.a -lthread_db
> linux-low.o: In function `linux_create_inferior':
> linux-low.c:(.text+0x25d2): undefined reference to `fork'
> linux-ptrace.o: In function `linux_child_function':
> linux-ptrace.c:(.text+0x24): undefined reference to `fork'
> linux-ptrace.o: In function `linux_check_ptrace_features':
> linux-ptrace.c:(.text+0x10a): undefined reference to `fork'
> thread-db.o: In function `thread_db_init':
> thread-db.c:(.text+0x520): undefined reference to `td_thr_tlsbase'
> collect2: error: ld returned 1 exit status

That won't help you here either (at least for this specific
problem). It is the exec step this program that is failing.


> I searched the internet and found that it might be stack size
> related. But even compiling example code and C library with
> -Wl,-elf2flt=-s16384 didn't help.

Ok, that is always a good thing to try first.


> Any help is appreciated,

The verbose elf2flt output may give some clues. You may need to
instrument the kernel's fs/binfmt_flat.c code to match up reloc
numbers though if nothing is obviously wrong in the verbose
reloc information.

Regards
Greg


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