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docs: Add a generic loader explanation document

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Signed-off-by: Alistair Francis <alistair.francis@xilinx.com>
Reviewed-by: Peter Maydell <peter.maydell@linaro.org>
Message-id: 9d991a2df990cf55e2630410a5a03ea48930af5d.1475195078.git.alistair.francis@xilinx.com
Signed-off-by: Peter Maydell <peter.maydell@linaro.org>
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Alistair Francis 2016-10-04 13:28:09 +01:00 committed by Peter Maydell
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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. 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.
<force-raw> - Forces the file to be treated as a raw image. This can be
used to specify the load address of ELF files.
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