Re: [Qemu-devel] [PATCH v12 2/2] docs: Add a generic loader explanation document

[Markus Armbruster]

Alistair Francis <address@hidden> writes:

> Signed-off-by: Alistair Francis <address@hidden>
> Reviewed-by: Peter Maydell <address@hidden>
> ---
> V11:
>  - Fix corrections
> V10:
>  - Split the data loading and PC setting
> V9:
>  - Clarify the image loading options
> V8:
>  - Improve documentation
> V6:
>  - Fixup documentation
> V4:
>  - Re-write to be more comprehensive
>
>  docs/generic-loader.txt | 81 
> +++++++++++++++++++++++++++++++++++++++++++++++++
>  1 file changed, 81 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..d1f8ce3
> --- /dev/null
> +++ b/docs/generic-loader.txt
> @@ -0,0 +1,81 @@
> +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 Data into 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=<data-len>
> +                   [,data-be=<data-be>][,cpu-num=<cpu-num>]
> +
> +    <addr>      - The address to store the data in.
> +    <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>   - The number of the CPU's address space where the data should
> +                  be loaded. If not specified the address space of the first
> +                  CPU is used.
> +
> +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'.

Unless you bypassed QemuOpts number parsing somehow, octal works as
well.  In case you did bypass: don't!  Command line consistency matters.
Follow-up patch reverting the bypass would be required.

Not sure we want to document QemuOpts number syntax everywhere we
explain how a certain feature uses the command line.  A pointer to the
canonical place could be better.  Anyway, not something that needs
fixing before we commit.

> +
> +An example of loading value 0x8000000e to address 0xfd1a0104 is:
> +    -device loader,addr=0xfd1a0104,data=0x8000000e,data-len=4
> +
> +Setting a CPU's Program Counter
> +---------------------
> +The loader device allows the CPU's PC to be set from the command line. This
> +can be done by following the syntax below:
> +
> +     -device loader,addr=<addr>,cpu-num=<cpu-num>
> +
> +    <addr>      - The value to use as the CPU's PC.
> +    <cpu-num>   - The number of the CPU whose PC should be set to the
> +                  specified value.
> +
> +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 setting CPU 0's PC to 0x8000 is:
> +    -device loader,addr=0x8000,cpu-num=0
> +
> +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
> +                  CPU's address space. If not specified, the default is CPU 
> 0.

Using @cpu-num both for further specifying the meaning of @addr and for
setting that CPU's PC is awkward.  Are you sure there will never be a
use case where you need to specify the CPU without also setting its PC?

To be clear: while I feel this is a question we must discuss and
resolve, I don't think we need to hold the series for it.

> +    <force-raw> - Forces the file to be treated as a raw image. This can be
> +                  used to specify the load address of ELF files.

"Specifying the load address of an ELF file" sounds like loading a
position-independent ELF file at a particular address.  But I guess this
is actually for loading a file raw even though it is recognized by QEMU
as ELF.

> +
> +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

Naive question: if you want to more than one thing (where "thing" is one
of the three cases described above), do you need a separate -device for
each, or can you combine them into one?


Again, while my questions may lead to improvements, they can be applied
on top.