[SOLVED] Ozone script: Resolving vector address from elf file fails with GCC 5.0

rals · July 12, 2019 at 10:27 AM

Hello,

I'm having an issue debugging using an elf file compiled and linked with GNU ARM Embedded toolchain using GCC >= 5 (). The issue is not present in GNU ARM toolchain using GCC 4.9.

I'm not sure if this is the right forum, but at least I can share my findings with you.

Our flash layout reserves 0x8000 bytes at the start of the flash (0x08000000) for a bootloader.

Code

...


    bootloader (NOLOAD) :
    {
       _bootloader_start = .;
       /* Bootloader reservation */
       . = ORIGIN(flash) + _application_offset;
    } >flash
    .vectors :
    {
       . = ALIGN(0x100);
       _applicationBegin = .; 
       KEEP(*(.vectors))            /* Startup code */
    } >flash


...

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When debugging the application directly (ie. the bootloader is not executed) we expect the PC to be set to the application Reset_Handler function in the Ozone Event handler AfterTargetDownload()

Code

void AfterTargetDownload (void) {
  unsigned int SP;
  unsigned int PC;                                  
  unsigned int VectorTableAddr;                              
  VectorTableAddr = Elf.GetBaseAddr();
  if (VectorTableAddr == 0xFFFFFFFF) {
    Util.Log("Project file error: failed to get program base"); 
  } else {                                                        
    SP = Target.ReadU32(VectorTableAddr);                         
    Target.SetReg("SP", SP);                                    
    PC = Target.ReadU32(VectorTableAddr + 4);                     
    Target.SetReg("PC", PC);                                    
  }
}

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However, both PC and SP is set to zero.

Ozone console:
Elf.GetBaseAddr();
Target.SetReg ("SP", 0x0);
Target.SetReg ("PC", 0x0);

Here's a dump from readelf()

Code

arm-none-eabi-readelf -h artifacts\app_gcc_5.2.elf
ELF Header:
  Magic:   7f 45 4c 46 01 01 01 00 00 00 00 00 00 00 00 00
  Class:                             ELF32
  Data:                              2's complement, little endian
  Version:                           1 (current)
  OS/ABI:                            UNIX - System V
  ABI Version:                       0
  Type:                              EXEC (Executable file)
  Machine:                           ARM
  Version:                           0x1
  Entry point address:               0x803e859
  Start of program headers:          52 (bytes into file)
  Start of section headers:          15229296 (bytes into file)
  Flags:                             0x5000400, Version5 EABI, hard-float ABI
  Size of this header:               52 (bytes)
  Size of program headers:           32 (bytes)
  Number of program headers:         7
  Size of section headers:           40 (bytes)
  Number of section headers:         41
  Section header string table index: 38

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I'm no expert on elf files, but it seems that "Flags" is missing the "has entry point" (Flags should have been 0x5000402) which might cause Elf.GetBaseAddr() to return 0. When using GCC 4.9 using the same source/linker script "has entry point" is set.

As a workaround, I hardcoded VectorTableAddr to 0x08008000 in the Ozone project file, but it would be nice to know if I am doing anything wrong or missing an obvious gotcha.

SEGGER - Nino · July 12, 2019 at 3:55 PM

Hello,

Thank you for your inquiry.
It is possible that some markers are missing from the elf files depending on the compiler version.
Could you provide the elf file for reproduction?

Best regards,
Nino

rals · August 12, 2019 at 10:16 AM

Sorry for the delay - I've been on vacation.

I've attached an elf-file compiled with GCC 5.2 (https://launchpad.net/gcc-arm-embedded/5.0/5-2015-q4-major)

Best regards,

Rune

SEGGER - Nino · August 13, 2019 at 9:41 AM

Hello,

Thank you for providing the elf file.
There seems to be a misconception on how the Elf.GetBaseAddr(); command works. We have addressed this in the next revision of the manual so it is more clear.
Esentially GetBaseAddr will simply return the lowest address of your elf image. This can be the beginning of a vector table but can also be some kind of bootloader or other data.

To get the value of the Reset_Handler PC you can use ELF.GetEntryPointPC instead.

I hope this is more clear now.

Best regards,
Nino

[SOLVED] Ozone script: Resolving vector address from elf file fails with GCC 5.0

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