Generic Loader
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 QemuOpts 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 ELF, U-Boot, and Intel HEX executable formats as well as raw images. 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 memory address where the file should be loaded. This is required for raw images and ignored for non-raw files.
<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 the memory address where the raw file is loaded or the entry point specified in the executable format 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 supported executable formats as if they were raw.
All values are parsed using the standard QemuOpts 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.