_mainCRTStartup/ctr0.S and thumb

["Torsten at Robitzki dot de" <Torsten at Robitzki dot de>]

Hello,
I try to build software for an arm cortex-m0 (nordic nRF51422) target using binutils (2.24), gcc (4.9) and newlib (2.1.0). I've build newlib using following configure statement:

    CXX=g++-4.8 CC=gcc-4.8 ${PWD}/../configure --target=arm-none-eabi --prefix=/usr/local/arm-none-eabi --enable-interwork --enable-multilib --disable-nls


When I execute a very small C++ binary everything works fine until _mainCRTStartup gets called during startup. When I step through the code, step by step using a jtag debugger, I can follow the flow of execution till the first statement in _mainCRTStartup: 

here the output of arm-none-eabi-objdump -S

    000000c0 <_mainCRTStartup>:
	add	sl, sl, #256
    #endif
    #else
    #ifdef ARM_RDI_MONITOR
	/*  Issue Angel SWI to read stack info.  */
	movs	r0, #AngelSWI_Reason_HeapInfo
      c0:	e3b00016 	movs	r0, #22
	adr	r1, .LC0	/*  Point at ptr to 4 words to receive data.  */
      c4:	e28f10e8 	add	r1, pc, #232	; 0xe8
    ...


and here the output of the debugger:

    00000200:  06 48              LDR     R0, [PC, #+0x18]
    J-Link>s
    00000202:  00 47              BX      R0
    J-Link>s
    000000C0:  16 00              MOV     R6, R2
    J-Link>s
    000000C2:  B0 E3              B       #+0x760
    J-Link>s
    00000826:  C0 46              MOV     R8, R8
    ...

where 00000826 is somewhere in __fp_lock_all(). To me it looks like the cortex-m0 cpu interprets arm32 opcode as thumb code, right?

According to the linker map, /usr/local/arm-none-eabi/lib/gcc/arm-none-eabi/4.9.0/../../../../arm-none-eabi/lib/thumb/crt0.o is used and mapped to address c0. The disassembly of that file (using arm-none-eabi-objdump -S) yields:

    /usr/local/arm-none-eabi/lib/gcc/arm-none-eabi/4.9.0/../../../../arm-none-eabi/lib/thumb/crt0.o:     file format elf32-littlearm


    Disassembly of section .text:

    00000000 <_mainCRTStartup>:
            add     sl, sl, #256
    #endif
    #else
    #ifdef ARM_RDI_MONITOR
        /*  Issue Angel SWI to read stack info.  */
            movs    r0, #AngelSWI_Reason_HeapInfo
       0:   e3b00016        movs    r0, #22
            adr     r1, .LC0        /*  Point at ptr to 4 words to receive data.  */
       4:   e28f10e8        add     r1, pc, #232    ; 0xe8

can someone be so kind and shed some light on this? Any pointers on how to investigate this further are highly appreciated.

Kind regards,

Torsten