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

[Zong Li]

On Wed, Jul 22, 2026 at 11:56 AM Zong Li <zong.li at sifive.com> wrote:
>
> 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

Hi Anup,
Would you mind taking a look at this series when you have a moment?
Thanks