Bootstrap, the L4 kernel bootstrapper

Bootstrap Command Line Options

bootstrap and the kernel can be configured through command line switches. bootstrap is responsible for parsing both command lines: bootstrap options are the ones directly given to bootstrap, whereas kernel options are those directly given to the kernel, respectively.

When using Multiboot boot, the first module directly after bootstrap is considered the kernel: An example using GRUB2 might look like this:

multiboot /path/to/bootstrap bootstrap -bs-boolean-opt -bs-opt-with-argument=foo
module /path/to/fiasco fiasco -kernel-opt-with-argument=bar -kernel-boolean-opt

Note

The exact way to provide the command line to bootstrap is platform-dependent. On platforms supporting booting via Multiboot Specification the command line can be specified in the boot configuration (currently x86/amd64 only, e.g. using GRUB) whereas other platforms need the command line to be compiled into the bootstrap binary.

Platforms utilising flattened device trees usually also allow specifying a command line through the DT. This mechanism is not currently supported in bootstrap!

 

Note

bootstrap will ignore options it does not understand. For most cases, this also holds true if an option's arguments cannot be understood.

bootstrap options

Command line options directly understood by bootstrap itself are as follows (passed via bootstrap command line):

• -comirq=<irqno> (x86/amd64 only)

  If serial logging is enabled (default on), <irqno> defines which IRQ to use for serial port communication. This option is ignored if -noserial is also specified (see below).

• -comport=<portspec> (x86/amd64 only)

  If serial logging is enabled (default on), <portspec> defines which serial port to use, being one of:

  • <number>

    Use legacy port <number>, e.g. use -comport=1 for the port commonly known as COM1, or

  • pci:<card>:<port>

    Use serial port number <port> at PCI card number <card>, e.g. use -comport=pci:0:1 for the second port on the first PCI card.

  • pci:probe

    Use this to have bootstrap autodiscover all PCI serial lines. On each discovered line a message will be displayed, telling the correct <portspec> to be given to use the respective line.

  Note

  bootstrap does not support specifying the serial port's baudrate and always uses 115200 bps.

• -noserial

  Disable serial logging.

• -wait

  Wait for key press at early startup.

  Note

  This is not to be confused with the kernel's -wait option, see below.

• -maxmem=<mbytes>

  Limit the available memory to at most <mbytes> MiB.

• -mem=<size>@<offset>

  Add a region of memory of <size> at <offset> to the system's memory map. Both <size> and <offset> may be suffixed by either G, M, or K/k to denote GiB, MiB, or KiB, respectively.

  This option may be specified multiple times. If the option is not given, a platform-specific method for determining the memory layout will be used, if available.

• -presetmem=<intval>

  Initialise memory regions with <intval> before starting the kernel.

• -modaddr=<paddr>

  Relocate modules to the physical address <paddr>. Use this when utilising a version of GRUB that lacks support for the modaddr command.

Kernel Options

Command line options for the kernel (passed on kernel command line, i.e. to first module) bootstrap understands are as follows.

Note

Availability of individual options might depend on used platform and/or actual kernel configuration.

• -wait

  Enter debugger directly after startup, prior to executing any task.

• -serial_esc

  Enable entering the debugger over serial line by pressing Esc.

• -noserial

  Disable serial logging.

  Note

  If this is given as kernel command line argument, it does not affect bootstrap but only the kernel.

• -noscreen

  Disable VGA console.

• -esc

  Enable entering the debugger by pressing Esc on attached keyboard.

• -nojdb

  Disable the kernel debugger.

• -nohlt

  Enable quirk for broken HLT instruction.

• -apic

  Use Advanced Programmable Interrupt Controller (APIC) if available and known to be well-behaving.

• -loadcnt

  Use load counter for performance counting.

• -watchdog

  Enable watchdog timer.

• -irq0

  Allow IRQ 0 to be used by userland. This enables some sanity checks to ensure IRQ 0 is not used by the kernel, e.g. for profiling or scheduling purposes. This only has an effect on x86.

• -nosfn

  Disable SFN (special fully nested) mode of interrupt controller. This only has an effect on x86 with PIC8259 interrupt controller.

• -jdb_never_stop

  Prevent system from stopping to enter JDB. This only has an effect on x86.

• -kmemsize=<kbytes>

  Reserve <kbytes> KiB of memory for the kernel.

• -tbuf_entries=<number>

  Specify the <number> of trace buffer entries.

• -out_buf=<length>

  Specify length of console buffer to be <length> bytes.

• -jdb_cmd=<ctrlseq>

  Execute JDB command sequence <ctrlseq> right after start-up. If -wait is also given, <ctrlseq> is executed right before entering JDB.