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.
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.