Asymmetric partition sizes for monolithic self-updates

[bigbrett]

Allows UPDATE to be sized independently from BOOT to save a huge amount of flash when using monolithic self-updates. Without this fix, the BOOT partition wastes sizeof(wolfBoot) bytes, since only UPDATE needs to store the full monolithic payload.

[Copilot]

Pull request overview

This pull request adds support for asymmetric BOOT vs UPDATE partition sizing specifically for monolithic self-updates, so the UPDATE slot can stage a full monolithic payload without forcing the BOOT slot to be the same (larger) size.

Changes:

• Introduces WOLFBOOT_PARTITION_UPDATE_SIZE (defaulting to WOLFBOOT_PARTITION_SIZE) with compile-time constraints to keep swap-based modes symmetric.
• Updates signing/tooling, partition boundary checks, and erase/write logic to use the UPDATE slot size where appropriate.
• Updates documentation and example configurations to describe and demonstrate independent UPDATE sizing.

Reviewed changes

Copilot reviewed 15 out of 15 changed files in this pull request and generated 3 comments.

Show a summary per file

File	Description
tools/test.mk	Simulator self-update test now sizes/places the pBOOT trailer using UPDATE-size when provided.
tools/keytools/sign.c	Sign tool can validate self-update images against UPDATE partition size when set; improves error handling paths.
stage1/Makefile	Propagates WOLFBOOT_PARTITION_UPDATE_SIZE into generated build artifacts via template substitution.
src/update_flash.c	Adds a monolithic self-update size guard to prevent installed span from reaching into the UPDATE staging region.
src/libwolfboot.c	Uses UPDATE partition size for UPDATE erase, NSC range checks, and UPDATE trailer placement.
src/image.c	Makes fixed-partition size checks/trailer pointer depend on whether the image is in BOOT vs UPDATE.
Makefile	Exports WOLFBOOT_PARTITION_UPDATE_SIZE to the signing tool and injects it into include/target.h.
include/wolfboot/wolfboot.h	Defines and constrains WOLFBOOT_PARTITION_UPDATE_SIZE (monolithic-only for asymmetry; disallowed with ENCRYPT).
include/target.h.in	Adds optional UPDATE-size definition and updates overlap checks to use UPDATE-size.
docs/lib.md	Clarifies slot-size enforcement for BOOT vs UPDATE.
docs/flash_partitions.md	Documents the monolithic exception allowing a larger UPDATE partition.
docs/firmware_update.md	Adds detailed guidance for independent partition sizing and sizing math/constraints.
docs/compile.md	Documents WOLFBOOT_PARTITION_UPDATE_SIZE and its constraints.
config/examples/sim-self-update-monolithic.config	Updates the simulator example to an asymmetric BOOT/UPDATE layout.
config/examples/aurix-tc375-hsm-monolithic-update-wolfHSM-certs-rsa4096.config	Adds a new example configuration demonstrating asymmetric monolithic layout on AURIX TC375 + HSM.

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[wolfSSL-Fenrir-bot]

Fenrir Automated Review — PR #861

Scan targets checked: wolfboot-bugs, wolfboot-src

Findings: 4
4 finding(s) posted as inline comments (see file-level comments below)

This review was generated automatically by Fenrir. Findings are non-blocking.

[wolfSSL-Fenrir-bot]

Fenrir Automated Review — PR #861

Scan targets checked: none
Failed targets: wolfboot-bugs, wolfboot-src

⚠️ Review incomplete — one or more scan targets failed before findings could be produced. See the Fenrir PR review detail page for logs.

[wolfSSL-Fenrir-bot]

Fenrir Automated Review — PR #861

Scan targets checked: none
Failed targets: wolfboot-bugs, wolfboot-src

⚠️ Review incomplete — one or more scan targets failed before findings could be produced. See the Fenrir PR review detail page for logs.