Meaning
Placement of data and code segments at specific byte addresses within an executable file ensures that the hardware can load and execute them efficiently. Modern processors often require that instruction blocks start at addresses divisible by four or eight. If elf section alignment is incorrect, the memory management unit might trigger a fault or suffer a performance penalty during access.
Boundary Calculation
Compilers insert padding bytes between sections to meet the requirements of the target architecture. When the executable and linkable format (elf) file is parsed, the loader expects these sections to sit on specific page boundaries. This layout allows the operating system to apply different memory protections to code and data.
A code section might be marked read-only while the data section remains read-write.
Processor Efficiency
Fetching data from an unaligned address forces the CPU to perform multiple memory cycles. Correct elf section alignment enables single-cycle access for instructions and variables. In low-power devices, these extra cycles consume battery life and increase the execution time of critical radio tasks.
Linker Scripting
Control over the final layout of the binary is exercised through the configuration of the linking tool. The script specifies the start and end points for every section while enforcing the necessary padding. By tuning the elf section alignment, an engineer can optimize the use of internal SRAM and external flash.
Precision in these settings ensures the firmware fits within the constraints of the hardware module.
