[PATCH v3] docs: Correct FW_JUMP_FDT_ADDR calculation example

[Andrew Jones]

On Thu, Mar 30, 2023 at 10:46:57AM +0200, Andrew Jones wrote:
> T+cdxBr0t+JJwe at errol.ini.cmu.edu>
>  <261bbbfc531fa4a479e97e70933d5e722e7a8ab6.camel at 126.com>
>  <3be5bff68835974783ecf7231dc4eac0140d9be1.camel at 126.com>
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> In-Reply-To: <3be5bff68835974783ecf7231dc4eac0140d9be1.camel at 126.com>
> 
> On Thu, Mar 30, 2023 at 04:20:30PM +0800, Xiang W wrote:
> > 在 2023-03-30星期四的 16:13 +0800，Xiang W写道：
> > > 在 2023-03-29星期三的 23:13 -0400，Gabriel L. Somlo写道：
> > > > On Thu, Mar 30, 2023 at 10:15:59AM +0800, Xiang W wrote:
> > > > > 在 2023-03-24星期五的 08:07 -0400，Gabriel Somlo写道：
> > > > > > When using `PLATFORM=generic` defaults, the kernel is loaded at
> > > > > > `FW_JUMP_ADDR`, and the FDT is loaded at `FW_JUMP_FDT_ADDR.
> > > > > > 
> > > > > > Therefore, the maximum kernel size before `FW_JUMP_FDT_ADDR` must
> > > > > > be increased is `$(( FW_JUMP_FDT_ADDR - FW_JUMP_ADDR ))`.
> > > > > > 
> > > > > > The example calculation assumes `rv64`, and is wrong to boot
> > > > > > (off by 0x200000). Fix it and update it for the general case.
> > > > > > 
> > > > > > Signed-off-by: Gabriel Somlo <gsomlo at gmail.com>
> > > > > > ---
> > > > > >  docs/firmware/fw_jump.md | 16 ++++++++--------
> > > > > >  1 file changed, 8 insertions(+), 8 deletions(-)
> > > > > > 
> > > > > > diff --git a/docs/firmware/fw_jump.md b/docs/firmware/fw_jump.md
> > > > > > index 956897e..ed3a43e 100644
> > > > > > --- a/docs/firmware/fw_jump.md
> > > > > > +++ b/docs/firmware/fw_jump.md
> > > > > > @@ -46,15 +46,15 @@ follows:
> > > > > >    You can use the following method.
> > > > > >  
> > > > > >    ```
> > > > > > -  ${CROSS_COMPILE}objdump -h $KERNEL_ELF | sort -k 5,5 | awk -n '/^ +[0-9]+ /\
> > > > > > -  {addr="0x"$3; size="0x"$5; printf "0x""%x\n",addr+size}' \
> > > > > > -  | (( `tail -1` > 0x2200000 )) && echo fdt overlaps kernel,\
> > > > > > -  increase FW_JUMP_FDT_ADDR
> > > > > > +  ${CROSS_COMPILE}objdump -h $KERNEL_ELF | sort -k 5,5 | awk -n '
> > > > > > +  /^ +[0-9]+ / {addr="0x"$3; size="0x"$5; printf "0x""%x\n",addr+size}' |
> > > > > > +  (( `tail -1` > (FW_JUMP_FDT_ADDR - FW_JUMP_ADDR) )) &&
> > > > > FW_JUMP_FDT_ADDR and FW_JUMP_ADDR should be variables in the shell,
> > > > > and references need to use $ as the starting char.
> > > > 
> > > > AFAIK, "ARITHMETIC EVALUATION" rules in bash allow shell variables to
> > > > be referenced without the "parameter expansion syntax" (i.e., $FOO),
> > > > when they are within an expression (e.g., "(( FOO + BAR ))").
> > > 
> > > It is better to use POSIX shell, if want to use BASH it is better to
> > > add some text description
> > Sorry!!! This is POSIX grammar!!!
> 
> ((..)) is undefined for POSIX, only $((..)) is defined, but do we care?
> This is just an example in a document, not a script expected to run as
> part of the build on multiple platforms. Maybe we could change the
> sentence above to point out Bash though,
> 
>    ensure *FW_JUMP_FDT_ADDR* is set high enough to avoid overwriting the kernel.
> -  You can use the following method.
> +  Using Bash, you can use the following method:
> 
>    ```

Or, we can make more use of [posix] awk and make everything posix
compatible

${CROSS_COMPILE}objdump -h $KERNEL_ELF | sort -k 5,5 |
awk -P -v maxsize=$((FW_JUMP_FDT_ADDR - FW_JUMP_ADDR)) '
/^ +[0-9]+ / {
  addr="0x"$3; size="0x"$5; size+=addr;
}
END {
  if (size > maxsize) {
    print "fdt overlaps kernel, increase FW_JUMP_FDT_ADDR";
  }
}'

Thanks,
drew