niklasad1/elf2tab

elf2tab is a tool that converts Tock userland apps from .elf files to Tock Application Bundles (TABs or .tab files). TABs are Tock apps that have been compiled for the various architectures that Tock runs on.

Usage

Usage: elf2tab [-o OUTFILE] ELFFILE [ELFFILE...]

Options:
    -o OUTFILE                      set output file name
    -n PACKAGE_NAME                 set package name
    --stack STACK_SIZE              set stack size in bytes
    --app-heap APP_HEAP_SIZE        set app heap size in bytes
    --kernel-heap KERNEL_HEAP_SIZE  set kernel heap size in bytes
    -v, --verbose                   be verbose

For example, converting a "blink" app from a compiled .elf file (for a Cortex-M4 device) with this tool would look like:

$ elf2tab -o blink.tab -n blink --stack 1024 --app-heap 1024 --kernel-heap 1024 cortex-m4.elf

It also supports (and encourages!) combing .elf files for multiple architectures into a single tab:

$ elf2tab -o blink.tab -n blink --stack 1024 --app-heap 1024 --kernel-heap 1024 cortex-m0.elf cortex-m3.elf cortex-m4.elf

Compiling elf2tab

With rustup installed, simply run:

cargo build

elf2tab Details

elf2tab tries to be as generic as possible for creating apps that can be flashed onto a Tock board. It does three main things:

Extracts the various sections in each .elf file and creates a binary file per .elf from the sections.
Prepends a Tock Binary Format header to each binary.
Creates the TAB file by creating a tar file with each of the Tock binaries.

Creating binary files from .elf files

elf2tab tries to process .elf files in as generic of a way as possible. To create the binary file, elf2tab iterates through the sections in the .elf file in their offset order that are writeable, executable, or allocated, have nonzero length, and are of type PROGBITS. The binary data for each of these sections are concatenated into the output file.

Next, elf2tab appends to the binary all writeable or allocated sections that contain the string .rel in their name. Because of how these sections are created for PIC code by the linker, it seems these sections have to be special cased and not grouped into the first step.

Creating the TBF Header

All Tock apps must start with a Tock Binary Format header so that the kernel knows how big the app is, how much memory it requires, and other important properties. elf2tab handles creating this header automatically, and mostly just requires the --stack, --app-heap, and --kernel-heap flags so it knows the memory requirements.

However, the TBF header also contains information about "writeable flash regions", or portions of the application's address space in flash that the app intends to use to store persistent data. This information is added to the header so that the kernel and other tools know that there is persistent that should be maintained intact. To specify to elf2tab that a linker section is one of these writeable flash regions, the name of the section should include the string .wfr. Any sections in the .elf that include .wfr in their name will have their relative address offset included in the TBF header via the TbfHeaderWriteableFlashRegions TLV.

Creating the TAB file

After generating the program binary and TBF header for each .elf file specified in the command line, elf2tab will store those files along side the .elf files (using the .tbf extension), and create a TAB file containing each .tbf file. These .tab files are used by tools like Tockloader to load Tock apps on to boards.

Inspecting TABs

Tockloader can show some details of a .tab file. Simply:

$ tockloader inspect-tab <tab file name>

niklasad1 / elf2tab