[PATCH 0/7] firmware: add FW_DYNAMIC_APPEND firmware type

[Zong Li]

On Tue, Jul 7, 2026 at 11:39 AM Zong Li <zong.li at sifive.com> wrote:
>
> This series adds a fourth OpenSBI firmware type, FW_DYNAMIC_APPEND, next to
> the existing FW_DYNAMIC, FW_JUMP and FW_PAYLOAD.
>
> Motivation
> ==========
>
> FW_DYNAMIC requires the previous booting stage to build a struct
> fw_dynamic_info in memory and pass its address in a2. Some booting stages
> cannot easily allocate and pass such a structure, but they can load the
> OpenSBI image and patch a few words at a known location before jumping to
> it. FW_DYNAMIC_APPEND targets exactly that case: the struct fw_dynamic_info
> is appended into the OpenSBI binary and patched in place by the previous
> stage. For example, the previous boot stage runs on a dedicated hart.
> Therefore, it cannot set up CSRs of another hart that runs OpenSBI.
> This scenario will occurs in server systems with secure boot.
>
> Key design points
> =================
>
>   - The appended struct fw_dynamic_info is placed immediately before .bss.
>     .bss is NOBITS and is dropped by 'objcopy -O binary', so a structure
>     after it would not be part of the flat .bin. Placing it before .bss
>     makes it the last PROGBITS content, i.e. it sits at the tail of the
>     .bin and can be located from the image size. The previous booting
>     tage can therefore find the structure at:
>
>         load_address + binary_file_size - sizeof(struct fw_dynamic_info)
>
>   - struct fw_dynamic_info gains a new 'boot_dtb' field (info version 3)
>     to carry the DTB address. Existing offsets are unchanged.
>
>   - The previous booting stage patches every field at runtime. The
>     reservation is a KEEP() PROGBITS section, so the zero-initialised
>     bytes still land at the tail of the .bin.
>
>   - On the cold-boot path (guarded by FW_DYNAMIC_APPEND), fw_base.S calls
>     fw_dynamic_append_boot_args() in fw_dynamic_append.S. The helper sets
>     a0 = mhartid, a2 = &appended struct, and a1 = boot_dtb, and clears the
>     reserved a3/a4 that fw_platform_init consumes. Only a0-a4 are handled
>     here, the remaining GPRs are already cleared by the existing _reset_regs
>     later on the cold path. The boot_dtb load is gated on info version 3, so
>     an older layout leaves a1 = 0 instead of reading past the struct.
>
> Backward compatibility
> ======================
>
> All changes for the existing three firmware types are compiled out: the
> fw_base.S fixup and the .fw_dynamic_info output section are under
> #ifdef FW_DYNAMIC_APPEND, which is defined only by fw_dynamic_append.S and
> fw_dynamic_append.elf.ldS. FW_DYNAMIC, FW_JUMP and FW_PAYLOAD binaries are
> byte-for-byte unchanged.
>
> Build
> =====
>
>   make PLATFORM=<platform_subdir> FW_DYNAMIC_APPEND=y
>
> On the generic platform FW_DYNAMIC_APPEND=y is set in
> platform/generic/objects.mk, so it is built by default.
>
> Zong Li (7):
>   firmware: fw_dynamic: add boot_dtb field to struct fw_dynamic_info
>   firmware: fw_base.ldS: add .fw_dynamic_info output section before .bss
>   firmware: add fw_dynamic_append firmware type
>   firmware: fw_base.S: call fw_dynamic_append_boot_args on cold boot
>   firmware: build and enable the FW_DYNAMIC_APPEND firmware type
>   docs: firmware: document the FW_DYNAMIC_APPEND firmware type
>   docs: firmware: list FW_DYNAMIC_APPEND in fw.md
>
>  docs/firmware/fw.md                |  19 ++++-
>  docs/firmware/fw_dynamic_append.md | 110 +++++++++++++++++++++++++++++
>  firmware/external_deps.mk          |   1 +
>  firmware/fw_base.S                 |  11 +++
>  firmware/fw_base.ldS               |  24 +++++++
>  firmware/fw_dynamic_append.S       | 106 +++++++++++++++++++++++++++
>  firmware/fw_dynamic_append.elf.ldS |  24 +++++++
>  firmware/objects.mk                |   2 +
>  include/sbi/fw_dynamic.h           |  17 ++++-
>  platform/generic/objects.mk        |   1 +
>  platform/template/objects.mk       |   9 +++
>  11 files changed, 322 insertions(+), 2 deletions(-)
>  create mode 100644 docs/firmware/fw_dynamic_append.md
>  create mode 100644 firmware/fw_dynamic_append.S
>  create mode 100644 firmware/fw_dynamic_append.elf.ldS
>
> --
> 2.43.7
>

Hi Anup,
Could I know your perspective on this series. I would appreciate it if
you could let me know if it is ready to move forward. Thanks