mirror of
https://github.com/riscv-software-src/opensbi.git
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d4d2582eef
Now opensbi can run at any address via dynamic relocation. We can remove FW_TEXT_START. Signed-off-by: Xiang W <wxjstz@126.com> Reviewed-by: Anup Patel <anup@brainfault.org> Tested-by: Anup Patel <anup@brainfault.org>
79 lines
3.6 KiB
Markdown
79 lines
3.6 KiB
Markdown
OpenSBI Firmware with Jump Address (FW_JUMP)
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============================================
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OpenSBI **firmware with Jump Address (FW_JUMP)** is a firmware which only
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handles the address of the next booting stage entry, e.g. a bootloader or an OS
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kernel, without directly including the binary code for this next stage.
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A *FW_JUMP* firmware is particularly useful when the booting stage executed
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prior to the OpenSBI firmware is capable of loading both the OpenSBI firmware
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and the booting stage binary to follow the OpenSBI firmware.
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*FW_JUMP* Compilation
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---------------------
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A platform *FW_JUMP* firmware can be enabled by any of the following methods:
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1. Specifying `FW_JUMP=y` on the top level `make` command line.
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2. Specifying `FW_JUMP=y` in the target platform *objects.mk* configuration file.
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The compiled *FW_JUMP* firmware ELF file is named *fw_jump.elf*. Its expanded
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image file is *fw_jump.bin*. Both files are created in the platform-specific
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build directory under the *build/platform/<platform_subdir>/firmware* directory.
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*FW_JUMP* Firmware Configuration Options
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----------------------------------------
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To operate correctly, a *FW_JUMP* firmware requires some configuration
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parameters to be defined using either the top level `make` command line or the
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target platform *objects.mk* configuration file. The possible parameters are as
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follows:
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* **FW_JUMP_ADDR** - Address of the entry point of the booting stage to be
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executed following OpenSBI firmware. This address generally corresponds
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exactly to the address where this next booting stage was loaded.
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At least one of *FW_JUMP_ADDR* and *FW_JUMP_OFFSET* (see below) should be
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defined. Compilation errors will result from not defining one of them.
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* **FW_JUMP_OFFSET** - Address offset from the opensbi load address where the
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entry point of the next booting stage is located. This offset is used as
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relocatable address of the next booting stage entry point. If *FW_JUMP_ADDR*
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is also defined, the firmware will prefer *FW_JUMP_ADDR*.
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* **FW_JUMP_FDT_ADDR** - Address where the *flattened device tree (FDT file)*
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passed by the prior booting stage will be placed in memory before executing
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the booting stage following the OpenSBI firmware. If this option is not
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provided, then the OpenSBI firmware will pass the FDT address passed by the
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previous booting stage to the next booting stage.
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When using the default *FW_JUMP_FDT_ADDR* with *PLATFORM=generic*, you must
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ensure *FW_JUMP_FDT_ADDR* is set high enough to avoid overwriting the kernel.
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You can use the following method (e.g., using bash or zsh):
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```
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${CROSS_COMPILE}objdump -h $KERNEL_ELF | sort -k 5,5 | awk -n '
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/^ +[0-9]+ / {addr="0x"$3; size="0x"$5; printf "0x""%x\n",addr+size}' |
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(( `tail -1` > (FW_JUMP_FDT_ADDR - FW_JUMP_ADDR) )) &&
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echo fdt overlaps kernel, increase FW_JUMP_FDT_ADDR
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${LLVM}objdump -h --show-lma $KERNEL_ELF | sort -k 5,5 | awk -n '
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/^ +[0-9]+ / {addr="0x"$3; size="0x"$5; printf "0x""%x\n",addr+size}' |
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(( `tail -1` > (FW_JUMP_FDT_ADDR - FW_JUMP_ADDR) )) &&
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echo fdt overlaps kernel, increase FW_JUMP_FDT_ADDR
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```
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* **FW_JUMP_FDT_OFFSET** - Address offset from the opensbi load address where
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the FDT will be passed to the next booting stage. This offset is used
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as relocatable address of the FDT passed to the next booting stage. If
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*FW_JUMP_FDT_ADDR* is also defined, the firmware will prefer
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*FW_JUMP_FDT_ADDR*.
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*FW_JUMP* Example
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-----------------
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The *[qemu/virt]* platform illustrates how to configure and use a *FW_JUMP*
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firmware. Detailed information regarding these platforms can be found in the
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platform documentation files.
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[qemu/virt]: ../platform/qemu_virt.md
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