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Re: vector.s branch 0 problem


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Alexandre wrote:
> Doesn't the call for "-Ttarget.ld" in the arm-elf-gcc command make the
> link ?
> 
> Those are the commands I use to compile my project under eclipse:
> 
> make
> INSTALL_DIR=/ecos-c/Projets/workspace/eCos-KernelBuild/IAR-LPC2106_install/
> all
> arm-elf-gcc -c -o boot.o
> -I/ecos-c/Projets/workspace/eCos-KernelBuild/IAR-LPC2106_install//include
> -Wa,-adhlns=boot.lst -mcpu=arm7tdmi -mno-short-load-words -Wall
> -Wpointer-arith -Wstrict-prototypes -Winline -Wundef
> -Woverloaded-virtual -g -O2 -ffunction-sections -fdata-sections
> -fno-rtti -fno-exceptions -fvtable-gc -finit-priority boot.c
> arm-elf-gcc -nostartfiles
> -L/ecos-c/Projets/workspace/eCos-KernelBuild/IAR-LPC2106_install//lib
> -Ttarget.ld -Wl,-Map=boot.map -mcpu=arm7tdmi -mno-short-load-words
> -Wl,--gc-sections -Wl,-static -g -nostdlib -o boot boot.o
> arm-elf-objdump -h -S -C boot.o > boot.lss
> 
> yet the boot.lss file I obtain as a result isn't by far resembling the
> vectors.lss i spoke earlier.
> Do i have to add a arm-elf-ld command after the arm-elf-gcc ones ?

No, but you *must* run 'arm-elf-objdumop' on "boot", not "boot.o"

> 
> On 7/2/07, Gary Thomas <gary@mlbassoc.com> wrote:
> Alexandre wrote:
>> Hi everyone,
> 
>> I may have a found why my ecos does not work at all but i'd like so
>> feedback on it.
>> I used the command:
>> arm-elf-objdump -h -S -C vectors.o > vectors.lss
>> to have a clearer view of what was going on at the init scale.
>> Everything seemed nice so far but this morning i noticed that on the
>> rom vectors init:
> 
>> Disassembly of section .vectors:
> 
>> 00000000 <__exception_handlers>:
>>   0:    eafffffe     b    0 <__exception_handlers>
>>   4:    e59ff018     ldr    pc, [pc, #24]    ; 24
> <.undefined_instruction>
>>   8:    e59ff018     ldr    pc, [pc, #24]    ; 28 <.software_interrupt>
>>   c:    e59ff018     ldr    pc, [pc, #24]    ; 2c <.abort_prefetch>
>>  10:    e59ff018     ldr    pc, [pc, #24]    ; 30 <.abort_data>
>>  14:    b4405f62     strltb    r5, [r0], -#3938
>>  18:    e59ff018     ldr    pc, [pc, #24]    ; 38 <.IRQ>
>>  1c:    e59ff018     ldr    pc, [pc, #24]    ; 3c <.FIQ>
> 
>> I'm not a real genius when it come to assembly language but seems to
>> me the thing just loops forever at address 0.
> 
>> I lurked a bit into vector.s and found the code that generated the
>> part above was that:
> 
>>        .global __exception_handlers
>> __exception_handlers:
>> #ifdef CYGSEM_HAL_ROM_RESET_USES_JUMP
>> // Assumption:  ROM code has these vectors at the hardware reset
> address.
>> // A simple jump removes any address-space dependencies [i.e. safer]
>>        b       reset_vector                    // 0x00
>> #else
>>        ldr     pc,.reset_vector                // 0x00
>> #endif
>>        ldr     pc,.undefined_instruction       // 0x04
>>        ldr     pc,.software_interrupt          // 0x08 start &&
> software
>> int
>>        ldr     pc,.abort_prefetch              // 0x0C
>>        ldr     pc,.abort_data                  // 0x10
>> #ifdef CYGNUM_HAL_ARM_VECTOR_0x14
>>        .word   CYGNUM_HAL_ARM_VECTOR_0x14
>> #else
>>        .word   0                               // unused
>> #endif
>>        ldr     pc,.IRQ                         // 0x18
>>        ldr     pc,.FIQ                         // 0x1C
> 
>> Now if we take a closer look at the code at 0, it is supposed to
>> branch to the start of the reset_vector. I noticed there's isn't a "."
>> (dot) at the start of the name, don't know if it's important or not
>> but as those are right from the cvs i thought it would be improper to
>> change it.
> 
>> Do you guys have any idea what comes wrong here ?
> 
> You're looking at "vectors.o", correct?  This doesn't work
> because the instruction you are looking at needs some additional
> "relocation" - in particular the address of 'reset_vector' - to
> be added into it.   This is done by the linker (arm-elf-ld).
> 
> Try looking at the same piece of code in the final ELF
> image and you'll see that it's quite different.
> 
> 
> 
>>

- --
- ------------------------------------------------------------
Gary Thomas                 |  Consulting for the
MLB Associates              |    Embedded world
- ------------------------------------------------------------
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