xemu/docs/generic-loader.txt

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.

All values are parsed using the standard QemuOps parsing. This allows the user
to specify any values in any format supported. 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

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.

All values are parsed using the standard QemuOps parsing. This allows the user
to specify any values in any format supported. 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. It can load raw
files and ELF executable files.  Raw files are loaded verbatim.  ELF executable
files are loaded by an ELF loader.  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.
    <force-raw> - Setting force-raw=on forces the file to be treated as a raw
                  image.  This can be used to load ELF files as if they were raw.

All values are parsed using the standard QemuOps parsing. This allows the user
to specify any values in any format supported. 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

Restrictions and ToDos
----------------------
 - At the moment it is just assumed that if you specify a cpu-num then you
   want to set the PC as well. This might not always be the case. In future
   the internal state 'set_pc' (which exists in the generic loader now) should
   be exposed to the user so that they can choose if the PC is set or not.