Re: [Qemu-devel] [PATCH v9 8/8] docs: Add a generic loader explanation document

[Peter Maydell]

On 14 July 2016 at 01:03, Alistair Francis <address@hidden> wrote:
> Signed-off-by: Alistair Francis <address@hidden>
> ---
> V9:
>  - Clarify the image loading options
> V8:
>  - Improve documentation
> V6:
>  - Fixup documentation
> V4:
>  - Re-write to be more comprehensive
>
>  docs/generic-loader.txt | 63 
> +++++++++++++++++++++++++++++++++++++++++++++++++
>  1 file changed, 63 insertions(+)
>  create mode 100644 docs/generic-loader.txt
>
> diff --git a/docs/generic-loader.txt b/docs/generic-loader.txt
> new file mode 100644
> index 0000000..16c11ee
> --- /dev/null
> +++ b/docs/generic-loader.txt
> @@ -0,0 +1,63 @@
> +Copyright (c) 2016 Xilinx Inc.
> +
> +This work is licensed under the terms of the GNU GPL, version 2 or later.  
> See
> +the COPYING file in the top-level directory.
> +
> +
> +The 'loader' device allows the user to load multiple images or values into
> +QEMU at startup.
> +
> +Loading Memory Values
> +---------------------
> +The loader device allows memory values to be set from the command line. This
> +can be done by following the syntax below:
> +
> +    -device loader,addr=<addr>,data=<data>,data-len=<len>
> +    -device loader,addr=<addr>,cpu-num=<cpu-num>
> +
> +    <addr>      - The address to store the data or the value to use as the
> +                  CPU's PC.
> +    <data>      - The value to be written to the address. The maximum size of
> +                  the data is 8 bytes.
> +    <data-len>  - The length of the data in bytes. This argument must be
> +                  included if the data argument is.
> +    <data-be>   - Set to true if the data to be stored on the guest should be
> +                  written as big endian data. The default is to write little
> +                  endian data.
> +    <cpu-num>   - This will cause the CPU to be reset and the PC to be set to
> +                  the value of addr.
> +
> +For all values both hex and decimal values are allowed. By default the values
> +will be parsed as decimal. To use hex values the user should prefix the 
> number
> +with a '0x'.
> +
> +An example of loading value 0x8000000e to address 0xfd1a0104 is:
> +    -device loader,addr=0xfd1a0104,data=0x8000000e,data-len=4
> +
> +Loading Files
> +-------------
> +The loader device also allows files to be loaded into memory. This can be 
> done
> +similarly to setting memory values. The syntax is shown below:
> +
> +    -device loader,file=<file>,addr=<addr>,cpu-num=<cpu-num>,force-raw=<raw>
> +
> +    <file>      - A file to be loaded into memory
> +    <addr>      - The addr in memory that the file should be loaded. This is
> +                  ignored if you are using an ELF (unless force-raw is true).
> +                  This is required if you aren't loading an ELF.
> +    <cpu-num>   - This specifies the CPU that should be used. This is an
> +                  optional argument and will cause the CPU's PC to be set to
> +                  where the image is stored or in the case of an ELF file to
> +                  the value in the header. This option should only be used
> +                  for the boot image.
> +                  This will also cause the image to be written to the 
> specified
> +                  CPUs address space.
> +    <force-raw> - Forces the file to be treated as a raw image. This can be
> +                  used to specify the load address of ELF files.
> +
> +For all values both hex and decimal values are allowed. By default the values
> +will be parsed as decimal. To use hex values the user should prefix the 
> number
> +with a '0x'.
> +
> +An example of loading an ELF file which CPU0 will boot is shown below:
> +    -device loader,file=./images/boot.elf,cpu-num=0

With this interface, you can specify a file to be loaded to CPU 2's
address space (via file=whatever,cpu-num=2) but you can't specify
a data value to be loaded to CPU 2's address space (because
addr=a,data=x,data-len=y,cpu-num=2 isn't valid). I think we could
usefully make that syntax do that.

This is probably most clearly documented by completely splitting
 -device loader,addr=<addr>,cpu-num=<cpu-num>
   (set the PC)

from
 -device 
loader,addr=<addr>,data=<data>,data-len=<data-len>[,data-be=<data-be>][,cpu-num=<cpu-num>]
   (load raw data values)

in the documentation in the same way that loader,file is split.

(I have a feeling we've been circling around on this option syntax
over the last few revisions so apologies if I've been inconsistent.)

You also can't specify a file to be loaded which doesn't set the
CPU PC, but I'm not sure how important that is. We can always add
it later with a no-set-pc option flag if we need it I guess.

thanks
-- PMM