[PATCH 1/1] docs/firmware: Update FW_JUMP documentation

[Jessica Clarke]

On 13 Sept 2022, at 06:46, Nylon Chen <nylon.chen at sifive.com> wrote:
> 
> From: "Nylon.Chen" <nylon.chen at sifive.com>
> 
> Add a tip for OpenSBI's Jump mode.
> 
> help user avoids the kernel overwritten.
> 
> Signed-off-by: Nylon Chen <nylon.chen at sifive.com>
> Signed-off-by: Nylon.Chen <nylon.chen at sifive.com>
> ---
> docs/firmware/fw_jump.md | 18 ++++++++++++++++++
> 1 file changed, 18 insertions(+)
> 
> diff --git a/docs/firmware/fw_jump.md b/docs/firmware/fw_jump.md
> index 35a4301..c20d722 100644
> --- a/docs/firmware/fw_jump.md
> +++ b/docs/firmware/fw_jump.md
> @@ -40,6 +40,24 @@ follows:
>   the booting stage following the OpenSBI firmware. If this option is not
>   provided, then the OpenSBI firmware will pass the FDT address passed by the
>   previous booting stage to the next booting stage.
> +  
> +  If your *PLATFORM=generic* and your *FW_JUMP_FDT_ADDR* is default, you must check
> +  your Linux size because Linux will be overwritten in OpneSBI's FDT copy loop.
> +  You can use the following method.

Use kernel not Linux, OpenSBI should be OS-agnostic.

> +
> +  ```
> +  LAST_SECTION=`${CROSS_COMPILE}objdump -h vmlinux | grep "00*" | awk '{print $5,$3}'\
> +  | sort -rfu | head -n 1 | awk '{split($0,addr," ");print addr[1]}'` \
> +  && LAST_SECTION_SIZE=`${CROSS_COMPILE}objdump -h vmlinux | grep "00*" |awk '{print $5,$3}'\
> +  | sort -rfu | head -n 1 | awk '{split($0,addr,"")}'` \
> +  && OFFSET_ADDR=$(( 16#$LAST_SECTION_SIZE + 16#$LAST_SECTION)) \
> +  && printf "The LMA of the last section of the Kernel is 0x%X\n" ${OFFSET_ADDR}
> +  ```

This uses GNU names for the tools, so won’t work with LLVM.

> +  
> +  If the result is bigger than the default of FW_JUMP_FDT_ADDR(0x2200000), 
> +  you must change it to avoid the problem of being overwritten.
> +
> +
> 
> *FW_JUMP* Example
> -----------------
> -- 
> 2.36.1
> 
> 
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