Why is that binary so big?

CodeSizer is a static code size profiling tool.

In size-focused embedded firmware development, the final binary is heavily inlined and link-time-optimised. A single function symbol may cover dozens of inlinees. CodeSizer uses objdump and addr2line to unwind the inline call stack at every instruction address, so code size can be attributed to the correct node in the inline call tree within each function.

The output is a static HTML report file, with a small amount of JavaScript for UI features like toggling expand/collapse of the tree view.

From the interactive help:

usage: codesizer.py [-h] [--cross-prefix CROSS_PREFIX] [--section SECTION]
                    elf output

Analyse static code size of an ELF file. Disassemble via objdump, unwind inline
call stacks via addr2line, and emit a static HTML report.

positional arguments:
  elf                   input ELF file
  output                output HTML file

options:
  -h, --help            show this help message and exit
  --cross-prefix CROSS_PREFIX
                        prefix for objdump and addr2line (default: riscv32-unknown-
                        elf-)
  --section, -j SECTION
                        Specify ELF section. Pass multiple times for multiple
                        sections. If unspecified, .text is used.

The correct toolchain must be present on your $PATH with the given prefix, or you must specify a full file path to the toolchain binaries. For example:

• If you've installed the gcc-arm-none-eabi package on Ubuntu, then use --cross-prefix=arm-none-eabi-.

• If you've installed a riscv-gnu-toolchain build at /opt/riscv/gcc15, then use --cross-prefix=/opt/riscv/gcc15/bin/riscv32-unknown-elf-.

This HTML report was generated by the following command:

./codesizer.py --cross-prefix arm-none-eabi- arm-bootrom.elf arm-bootrom.html -j .text -j .secure_gateways

The ELF file comes from the RP2350 A4 bootrom release.