Appending a checksum for application self‐checking - iarsystems/cmake-tutorial GitHub Wiki

This interactive example describes how to append a checksum for application self-checking.

• add_custom_target()
• Checksum calculation for verifying image integrity Arm | RH850 | RISC-V | RL78 | RX

A CMake project example is provided at examples/checksum:

The project links the executable target using the linker configuration from generic_cortex.icf for a Generic Arm Cortex device. In the linker configuration, a block is defined to hold all the read-only data followed by a a section named .checksum:

// This if() block is the relevant change for ielftool's checksum placement
if (!isempty(ROM_region))
{
  // Application block with ielftool checksum placeholder at end
  define block APP with fixed order {
    readonly,
    ro section .checksum
  };

  place in ROM_region  { block APP };
}

So that the checksum symbol will be placed right after the application ends.

The application uses the crc32() function from crc32.c to perform self-checking at initialization.

The .checksum placeholder should then be filled at build-time by the IAR ELF Tool (${CMAKE_IAR_ELFTOOL}) so that it can be downloaded into the target alongside the application. The interactive exercise will be to insert the IAR ELF Tool command to generate the checksum at build-time so that the application can perform self-check during the runtime.

• Perform the following task on CMakeLists.txt (click to show/hide answers):

add_custom_target(checksummed ALL
  DEPENDS checksum
  COMMAND ${CMAKE_IAR_ELFTOOL} 
    --silent #--verbose
    --fill="0xFF\;0x0000'0000-0x0007'FFFF"
    --checksum="__checksum:4,crc32:Li,0xFFFFFFFF\;0x0000'0000-__checksum"
    $<TARGET_FILE:checksum>
    $<TARGET_FILE:checksum>
)

• Build and test the project. Refer to the tutorial for more information.

• Perform the following task on main.c (click to show/hide answers):

__root const uint8_t data[16384] = { 0, 1 }; 

• Rebuild and test the project. Changing the data vector contents modified the application, hence a new checksum should be calculated, and yet, the consistency should be kept between the checksum etched to the application image at build time and the value yielded at runtime.

• Invoking IAR binary utilities