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

[Andrew Jones]

On Tue, Sep 13, 2022 at 01:46:05PM +0800, Nylon Chen 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.

Ensure FW_JUMP_FDT_ADDR is set high enough to avoid overwriting the
kernel.  The following method may be used to check if the default
(0x2200000) is sufficient:

> +
> +  ```
> +  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}
> +  ```

Once we've decided to use awk, we might as well use all of it

${CROSS_COMPILE}objdump -h $KERNEL_ELF | sort -k 5,5 |
        awk '/^ +[0-9]+ /                                                       \
        { s = strtonum("0x"$3) + strtonum("0x"$5) }                             \
        END {                                                                   \
                if (s > 0x2200000) {                                            \
                        print "fdt overlaps kernel, increase FW_JUMP_FDT_ADDR"; \
                        exit(1)                                                 \
                }                                                               \
        }'

Thanks,
drew

> +  
> +  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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