Re: [Qemu-devel] [PATCH v8 5/5] docs: Add a generic loader explanation document

[Alistair Francis]

On Tue, Jul 12, 2016 at 9:31 AM, Peter Maydell <address@hidden> wrote:
> On 2 July 2016 at 02:07, Alistair Francis <address@hidden> wrote:
>> Signed-off-by: Alistair Francis <address@hidden>
>> ---
>> V8:
>>  - Improve documentation
>> V6:
>>  - Fixup documentation
>> V4:
>>  - Re-write to be more comprehensive
>>
>>  docs/generic-loader.txt | 60 
>> +++++++++++++++++++++++++++++++++++++++++++++++++
>>  1 file changed, 60 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..34684fc
>> --- /dev/null
>> +++ b/docs/generic-loader.txt
>> @@ -0,0 +1,60 @@
>> +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. This option should only be used
>> +                  for the boot image.
>
> For an ELF file we use the start address specified in the ELF header, right?

Yes, I have specified that now in the docs.

>
> We also end up writing to that CPU's address space, but only for ELF files.

Yes, this will apply to all images in the next version.

>
>> +    <force-raw> - Forces the file to be treated as a raw image. This can be
>> +                  used to specify the load address of ELF files.
>
> Presumably it results in the ELF file being dumped into memory as a raw
> image without any regard to what the segment headers say about loading,
> offsets, etc?

Correct, I have made that more clear.

Thanks,

Alistair

>
>> +
>> +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
>
> thanks
> -- PMM
>