Build overview: Difference between revisions

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The SeaBIOS code can be built using standard GNU tools.  A recent Linux distribution should be able to build SeaBIOS using the standard compiler tools.
The SeaBIOS code can be built using standard GNU tools.  A recent
Linux distribution should be able to build SeaBIOS using the standard
compiler tools.


= Quick start =
= Building SeaBIOS =


For QEMU and KVM users, [[Download|obtain the code]] and run '''make'''.  The resulting binary image will be located in '''out/bios.bin'''.  For coreboot users, please see the [http://www.coreboot.org/SeaBIOS coreboot SeaBIOS page].
First, [[Download|obtain the code]].  SeaBIOS can be compiled for
several different build targets.  It is also possible to configure
additional compile time options - run '''make menuconfig''' to do
this.


It is possible to configure additional compile time options - run '''make menuconfig''' to do this.
== Build for QEMU (along with KVM, Xen, and Bochs) ==


= Testing images on QEMU =
To build for QEMU (and similar), one should be able to run "make" in
the main directory.  The resulting file "out/bios.bin" contains the
processed bios image.


To test under QEMU, one will need to create a directory with all the bios images and then overwrite the main bios image.  For example:
One can use the resulting binary with QEMU by using QEMU's "-bios"
option.  For example:


  cp /usr/share/qemu/*.bin mybiosdir/
  qemu -bios out/bios.bin -fda myfdimage.img
cp out/bios.bin mybiosdir/


Once this is setup, one can instruct QEMU to use the newly created directory for rom images.  For example:
One can also use the resulting binary with Bochs.  For example:


  qemu -L mybiosdir/ -fda myfdimage.img
  bochs -q 'floppya: 1_44=myfdimage.img' 'romimage: file=out/bios.bin'


For best results, please use QEMU version 0.12.0 or later.
== Build for coreboot ==


= Testing images on Bochs =
To build for coreboot please see the coreboot build instructions at:
http://www.coreboot.org/SeaBIOS


To test the bios under bochs, some config option changs are needed. Run '''make menuconfig''', set '''CONFIG_OPTIONROMS_DEPLOYED''', and unset '''CONFIG_MTRR_INIT'''.  Then one can run Bochs with the resulting bios.bin file - for example:
== Build as a UEFI Compatibility Support Module (CSM) ==


  bochs -q 'floppya: 1_44=myfdimage.img, status=inserted' 'romimage: file=out/bios.bin'
To build as a CSM, first run kconfig (make menuconfig) and enable
CONFIG_CSM. Then build SeaBIOS (make) - the resulting binary will be
in "out/Csm16.bin".


For best results, please use Bochs version 2.4.5 or later.
This binary may be used with the OMVF/EDK-II UEFI firmware. It will
provide "legacy" BIOS services for booting non-EFI operating systems
and will also allow OVMF to display on otherwise unsupported video
hardware by using the traditional VGA BIOS. (Windows 2008r2 is known
to use INT 10h BIOS calls even when booted via EFI, and the presence
of a CSM makes this work as expected too.)


= Debug information =
Having built SeaBIOS with CONFIG_CSM, one should be able to drop the
result (out/Csm16.bin) into an OVMF build tree at
OvmfPkg/Csm/Csm16/Csm16.bin and then build OVMF with 'build -D
CSM_ENABLE'. The SeaBIOS binary will be included as a discrete file
within the 'Flash Volume' which is created, and there are tools which
will extract it and allow it to be replaced.


SeaBIOS writes informational messages to a special debug port.
= Overview of files in the repository =
Under QEMU, one can view these messages using the ''isa-debugcon'' module.  For example:


  qemu -fda myfdimage.img -chardev stdio,id=seabios -device isa-debugcon,iobase=0x402,chardev=seabios
The '''src/''' directory contains the main bios source code.  The
'''src/hw/''' directory contains source code specific to hardware
drivers. The '''src/fw/''' directory contains source code for
platform firmware initialization. The '''src/std/''' directory
contains header files describing standard bios, firmware, and hardware
interfaces.


It's possible to increase the verbosity of the SeaBIOS debug information.  To do this, run '''make menuconfig''' and set '''CONFIG_DEBUG_LEVEL''' to a higher value. When reporting issues, please set the debug level to 8 (levels above 8 will frequently cause too much data) and include the full log along with a description of the problem in the trouble report.
The '''vgasrc/''' directory contains code for VGA BIOS
implementations. This code is separate from the main BIOS code in the
src/ directory. When the build is configured to produce a VGA BIOS the
resulting binary is found in out/vgabios.bin.  The VGA BIOS code is
always compiled in 16bit mode.


== Debugging with QEMU and GDB ==
The '''scripts/''' directory contains helper utilities for
manipulating and building the final roms.


The gdb-server mechanism of QEMU is also useful.  One can use gdb with QEMU to debug system images.  To use this, add '-s -S' to the QEMU command line. For example:
The '''out/''' directory is created by the build process - it contains
all intermediate and final files.


qemu -L mybiosdir/ -fda myfdimage.img -s -S
When reading the C code be aware that code that runs in 16bit mode can
 
not arbitrarily access non-stack memory - see [[Memory Model]] for
Then, in another session, run gdb with either out/rom16.o (to debug bios 16bit code) or out/rom32.o (to debug bios 32bit code).  For example:
more details.  For information on the major C code functions and where
 
code execution starts see [[Execution and code flow]].
gdb out/rom16.o
 
Once in gdb, use the command '''target remote localhost:1234''' to have gdb connect to qemu.  See the QEMU documentation for more information on using gdb and qemu in this mode.  Note that gdb seems to get breakpoints confused when the cpu is in 16-bit real mode.  This makes stepping through the program difficult (though 'step instruction' still works).  Also, one may need to set 16bit break points at both the cpu address and memory address (eg, break *0x1234 ; break *0xf1234).

Revision as of 19:41, 14 December 2014

The SeaBIOS code can be built using standard GNU tools. A recent Linux distribution should be able to build SeaBIOS using the standard compiler tools.

Building SeaBIOS

First, obtain the code. SeaBIOS can be compiled for several different build targets. It is also possible to configure additional compile time options - run make menuconfig to do this.

Build for QEMU (along with KVM, Xen, and Bochs)

To build for QEMU (and similar), one should be able to run "make" in the main directory. The resulting file "out/bios.bin" contains the processed bios image.

One can use the resulting binary with QEMU by using QEMU's "-bios" option. For example: 

qemu -bios out/bios.bin -fda myfdimage.img

One can also use the resulting binary with Bochs. For example: 

bochs -q 'floppya: 1_44=myfdimage.img' 'romimage: file=out/bios.bin'

Build for coreboot

To build for coreboot please see the coreboot build instructions at: http://www.coreboot.org/SeaBIOS

Build as a UEFI Compatibility Support Module (CSM)

To build as a CSM, first run kconfig (make menuconfig) and enable CONFIG_CSM. Then build SeaBIOS (make) - the resulting binary will be in "out/Csm16.bin".

This binary may be used with the OMVF/EDK-II UEFI firmware. It will provide "legacy" BIOS services for booting non-EFI operating systems and will also allow OVMF to display on otherwise unsupported video hardware by using the traditional VGA BIOS. (Windows 2008r2 is known to use INT 10h BIOS calls even when booted via EFI, and the presence of a CSM makes this work as expected too.)

Having built SeaBIOS with CONFIG_CSM, one should be able to drop the result (out/Csm16.bin) into an OVMF build tree at OvmfPkg/Csm/Csm16/Csm16.bin and then build OVMF with 'build -D CSM_ENABLE'. The SeaBIOS binary will be included as a discrete file within the 'Flash Volume' which is created, and there are tools which will extract it and allow it to be replaced.

Overview of files in the repository

The src/ directory contains the main bios source code. The src/hw/ directory contains source code specific to hardware drivers. The src/fw/ directory contains source code for platform firmware initialization. The src/std/ directory contains header files describing standard bios, firmware, and hardware interfaces.

The vgasrc/ directory contains code for VGA BIOS implementations. This code is separate from the main BIOS code in the src/ directory. When the build is configured to produce a VGA BIOS the resulting binary is found in out/vgabios.bin. The VGA BIOS code is always compiled in 16bit mode.

The scripts/ directory contains helper utilities for manipulating and building the final roms.

The out/ directory is created by the build process - it contains all intermediate and final files.

When reading the C code be aware that code that runs in 16bit mode can not arbitrarily access non-stack memory - see Memory Model for more details. For information on the major C code functions and where code execution starts see Execution and code flow.

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