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Date: Tue, 17 Feb 2015 01:41:00 +0000
From: David Guillen Fandos <>
Subject: Executable crashes at __libc_start_main


I'm creating an app which is an ARM ELF (linux) which runs in very small
machines (routers). Using buildroot to create my toolchain I can choose
between uClibc and musl. Using uclibc my binary crashes at loading, so I
switched to musl and tried. It fails too.

The problem seems to be at __libc_start_main, in this part:

        uintptr_t a = (uintptr_t)&__init_array_start;
        for (; a<(uintptr_t)&__init_array_end; a+=sizeof(void(*)()))
                (*(void (**)())a)();

I checked a little bit (dumping the map file) and I get:

.init_array     0x0000000000016230        0x4
                0x0000000000016230                PROVIDE
(__init_array_start, .)
 .init_array    0x0000000000016230        0x4
                0x0000000000016234                PROVIDE
(__init_array_end, .)

.fini_array     0x0000000000016234        0x4

Which tells me there is only one function pointer there. Now dumping the

00016230 <__frame_dummy_init_array_entry>:
   16230:       00008210        andeq   r8, r0, r0, lsl r2

Disassembly of section .fini_array:

Which is pointer 0x8210 which points to function:

00008210 <frame_dummy>:
    8210:       e92d4008        push    {r3, lr}
    8214:       e59f3034        ldr     r3, [pc, #52]   ; 8250
    8218:       e3530000        cmp     r3, #0


So far so good. The binary runs OK on a ARM machine running Debian, but
when I run this program on this other machine it crashes. The CPU is:

ARMv6-compatible processor rev 7 (v6l)
CPU implementer	: 0x41
CPU architecture: 6TEJ
CPU variant	: 0x0
CPU part	: 0xb76
CPU revision	: 7

Finally I got a core dump and the program crashes here:

    88c8:       e1550007        cmp     r5, r7
    88cc:       2a000003        bcs     88e0 <__libc_start_main+0x1b0>
    88d0:       e4953004        ldr     r3, [r5], #4
    88d4:       e1a0e00f        mov     lr, pc
    88d8:       e12fff13        bx      r3
    88dc:       eafffff9        b       88c8 <__libc_start_main+0x198>

In the 88d8 instruction to be more exact. Seems that R3 is holding the
value 0xc8000082!!! Where is that 0xC8 at the beginning comming from?
The PC reported by the core dump is 0xc8000080 which I guess it's just
the vlaue of R3 aligned to 4 byte boundary. R5 points to the right
place, it's just the value loaded by the load. Could it be that
something corrupts my ELF? Could it be the OS being really dumb at
loading the ELF? It's a pretty old kernel, 2.6.21.

Thanks a lot!


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