In this lesson we will be investigating OptionROM images with the help of BaseTools utility EfiRom. It is available in your path once you'll execute . edksetup.sh in edk2 folder.
First take a look at EfiRom help:
$ EfiRom -h
Usage: EfiRom -f VendorId -i DeviceId [options] [file name<s>]
Copyright (c) 2007 - 2018, Intel Corporation. All rights reserved.
Options:
-o FileName, --output FileName
File will be created to store the output content.
-e EfiFileName
EFI PE32 image files.
-ec EfiFileName
EFI PE32 image files and will be compressed.
-b BinFileName
Legacy binary files.
-l ClassCode
Hex ClassCode in the PCI data structure header.
-r Rev Hex Revision in the PCI data structure header.
-n Not to automatically set the LAST bit in the last file.
-f VendorId
Hex PCI Vendor ID for the device OpROM, must be specified
-i DeviceId
One or more hex PCI Device IDs for the device OpROM, must be specified
-p, --pci23
Default layout meets PCI 3.0 specifications
specifying this flag will for a PCI 2.3 layout.
-d, --dump
Dump the headers of an existing option ROM image.
-v, --verbose
Turn on verbose output with informational messages.
--version Show program's version number and exit.
-h, --help
Show this help message and exit.
-q, --quiet
Disable all messages except FATAL ERRORS.
--debug [#,0-9]
Enable debug messages at level #.
Complete version of the manual for EfiRom is placed at https://github.com/tianocore/edk2/blob/master/BaseTools/UserManuals/EfiRom_Utility_Man_Page.rtf
If you are interested in the source code: https://github.com/tianocore/edk2/tree/master/BaseTools/Source/C/EfiRom
With this tool it is possible to:
- dump Option ROM images
- create Option ROM images from EFI drivers and/or Legacy binary images
Also take a look at tianocore docs:
- https://edk2-docs.gitbook.io/edk-ii-basetools-user-guides/efirom
- https://edk2-docs.gitbook.io/edk-ii-uefi-driver-writer-s-guide/18_pci_driver_design_guidelines/readme.7/1871_efirom_utility
Preboot eXecution Environment (PXE) is a standard for booting to an image received via network (https://en.wikipedia.org/wiki/Preboot_Execution_Environment).
To know how to use particular PCI network card for PXE boot, BIOS needs to know some network card internals. But BIOS is not an OS, it is not possible to have drivers for every PCI network card in it. Therefore this problem is solved via OptionROM firmware. PCI network card contains all the necessary code for PXE boot in itself. But not every card have such firmware in itself. In this case you can utilize iPXE project.
iPXE is the open source network boot firmware (https://ipxe.org/). It provides a full PXE implementation enhanced with some additional features. It support various PCI network cards https://ipxe.org/appnote/hardware_drivers.
iPXE can be compiled as EFI application or as EFI/Legacy OptionROM. You can read more about build targets at https://ipxe.org/appnote/buildtargets.
Let's download iPXE:
git clone git://git.ipxe.org/ipxe.git
cd ipxe/src
Now build some images:
$ sudo apt-get install liblzma-dev
$ make bin-x86_64-efi/ipxe.efi # EFI app with all devices
$ make bin-x86_64-efi/8086100e.efirom # EFI ROM vendev: 8086:100e
$ make bin/8086100e.rom # Legacy ROM vendev: 8086:100e
You can execute ipxe.efi directly from the UEFI shell. It is a simple UEFI application similar to the ones that we create in this series.
Look at the https://github.com/ipxe/ipxe/blob/master/src/image/efi_image.c for source code investigation.
8086100e.rom is a Legacy code image PCI Option ROM for 8086:100e network card
8086100e.efirom is an UEFI code image PCI Option ROM for 8086:100e network card
If you inspect the OptionROM images with hexdump, you'll see standard AA55 and PCIR signatures in them.
$ hexdump bin/8086100e.rom -C -n 64
00000000 55 aa 86 e9 a2 00 30 00 00 00 00 00 00 00 00 00 |U.....0.........|
00000010 9c 00 00 00 00 00 84 00 1c 00 40 00 50 43 49 52 |..........@.PCIR|
00000020 86 80 0e 10 bf 04 1c 00 03 00 00 02 86 00 01 00 |................|
00000030 00 80 07 00 00 00 00 00 8d b4 00 00 8d b4 00 00 |................|
00000040
$ hexdump bin-x86_64-efi/8086100e.efirom -C -n 64
00000000 55 aa d0 00 f1 0e 00 00 0b 00 64 86 01 00 00 00 |U.........d.....|
00000010 00 00 00 00 00 00 38 00 1c 00 00 00 50 43 49 52 |......8.....PCIR|
00000020 86 80 0e 10 00 00 18 00 00 00 00 02 d0 00 00 00 |................|
00000030 03 80 00 00 87 00 00 00 0d 9e 01 00 00 d2 02 00 |................|
00000040
We can even use EfiRom on them:
$ EfiRom -d bin/8086100e.rom
Image 1 -- Offset 0x0
ROM header contents
Signature 0xAA55
PCIR offset 0x001C
Signature PCIR
Vendor ID 0x8086
Device ID 0x100E
Length 0x001C
Revision 0x0003
DeviceListOffset 0x4BF
Device list contents
0x100E
Class Code 0x020000
Image size 0x10C00
Code revision: 0x0001
MaxRuntimeImageLength 0x07
ConfigUtilityCodeHeaderOffset 0x00
DMTFCLPEntryPointOffset 0x00
Indicator 0x80 (last image)
Code type 0x00
If we execute EfiRom on a bin-x86_64-efi/8086100e.efirom, we would get an error:
$ EfiRom -d bin-x86_64-efi/8086100e.efirom
EfiRom: ERROR 1002: No PciRom input file
No *.rom input file
The problem is that we EfiRom understands only files with .rom extension, so change it and use EfiRom again:
$ cp bin-x86_64-efi/8086100e.efirom bin-x86_64-efi/8086100e.rom
$ EfiRom -d bin-x86_64-efi/8086100e.rom
Image 1 -- Offset 0x0
ROM header contents
Signature 0xAA55
PCIR offset 0x001C
Signature PCIR
Vendor ID 0x8086
Device ID 0x100E
Length 0x0018
Revision 0x0000
DeviceListOffset 0x00
Class Code 0x020000
Image size 0x1A000
Code revision: 0x0000
MaxRuntimeImageLength 0x00
ConfigUtilityCodeHeaderOffset 0x87
DMTFCLPEntryPointOffset 0x00
Indicator 0x80 (last image)
Code type 0x03 (EFI image)
EFI ROM header contents
EFI Signature 0x0EF1
Compression Type 0x0001 (compressed)
Machine type 0x8664 (X64)
Subsystem 0x000B (EFI boot service driver)
EFI image offset 0x0038 (@0x38)
EfiRom can't currently combine Option ROM from the EFI ROM images. But it can use EFI PE32 image files as a source for EFI ROM images in the resulting Option ROM. So we have to compile another target:
$ make bin-x86_64-efi/8086100e.efidrv
Now we can create combined OptionROM image with both Legacy and EFI ROMs.
$ EfiRom -f 0x8086 -i 0x100e -b bin/8086100e.rom -ec bin-x86_64-efi/8086100e.efidrv -o bin/8086100e_optionrom.rom
$ EfiRom -d bin/8086100e_optionrom.rom
Image 1 -- Offset 0x0
ROM header contents
Signature 0xAA55
PCIR offset 0x001C
Signature PCIR
Vendor ID 0x8086
Device ID 0x100E
Length 0x001C
Revision 0x0003
DeviceListOffset 0x4BF
Device list contents
0x100E
Class Code 0x020000
Image size 0x10C00
Code revision: 0x0001
MaxRuntimeImageLength 0x07
ConfigUtilityCodeHeaderOffset 0x00
DMTFCLPEntryPointOffset 0x00
Indicator 0x00
Code type 0x00
Image 2 -- Offset 0x10C00
ROM header contents
Signature 0xAA55
PCIR offset 0x001C
Signature PCIR
Vendor ID 0x8086
Device ID 0x100E
Length 0x001C
Revision 0x0003
DeviceListOffset 0x00
Class Code 0x000000
Image size 0x1A000
Code revision: 0x0000
MaxRuntimeImageLength 0x00
ConfigUtilityCodeHeaderOffset 0x00
DMTFCLPEntryPointOffset 0x00
Indicator 0x80 (last image)
Code type 0x03 (EFI image)
EFI ROM header contents
EFI Signature 0x0EF1
Compression Type 0x0001 (compressed)
Machine type 0x8664 (X64)
Subsystem 0x000B (EFI boot service driver)
EFI image offset 0x0038 (@0x10C38)
SeaBIOS is an open-source legacy BIOS implementation that implements the standard BIOS calling interfaces that a typical x86 proprietary BIOS implements (https://github.com/coreboot/seabios). SeaVGABIOS is a sub-project of the SeaBIOS project - it is an open source implementation of a 16bit X86 VGA BIOS (https://github.com/coreboot/seabios/blob/master/docs/SeaVGABIOS.md). In other words it builds a Legacy Option ROM for a PCI graphic device.
SeaBIOS uses Kconfig system for the build configuration. Main options for the VGA BIOS are placed under https://github.com/coreboot/seabios/blob/master/vgasrc/Kconfig In this file you can see that one of the options is a OptionROM with a Vendor/Device pair as 1234:1111. Exactly the one that we saw at QEMU:
config VGA_VID
depends on VGA_PCI
hex
prompt "PCI Vendor ID" if OVERRIDE_PCI_ID
default 0x1013 if VGA_CIRRUS
default 0x1002 if VGA_ATI
default 0x1234 if VGA_BOCHS_STDVGA
default 0x15ad if VGA_BOCHS_VMWARE
default 0x1b36 if VGA_BOCHS_QXL
default 0x1af4 if VGA_BOCHS_VIRTIO
default 0x100b if VGA_GEODEGX2
default 0x1022 if VGA_GEODELX
default 0x1234 if DISPLAY_BOCHS <--------------
default 0x0000
help
Vendor ID for the PCI ROM
config VGA_DID
depends on VGA_PCI
hex
prompt "PCI Vendor ID" if OVERRIDE_PCI_ID
default 0x00b8 if VGA_CIRRUS
default 0x5159 if VGA_ATI
default 0x1111 if VGA_BOCHS_STDVGA
default 0x0405 if VGA_BOCHS_VMWARE
default 0x0100 if VGA_BOCHS_QXL
default 0x1050 if VGA_BOCHS_VIRTIO
default 0x0030 if VGA_GEODEGX2
default 0x2081 if VGA_GEODELX
default 0x1111 if DISPLAY_BOCHS <---------------
default 0x0000
help
Device ID for the PCI ROM
If you wonder what is DISPLAY_BOCHS, here is a help for this option:
config DISPLAY_BOCHS
depends on QEMU
bool "qemu bochs-display support"
select VGA_EMULATE_TEXT
help
Build support for the qemu bochs-display device, which
is basically qemu stdvga without the legacy vga
emulation, supporting only 16+32 bpp VESA video modes
in a linear framebuffer. So this uses cbvga text mode
emulation.
The bochs-display device is available in qemu
v3.0+. The vgabios works with the qemu stdvga too (use
"qemu -device VGA,romfile=/path/to/vgabios.bin")".
Let's build this SeaBIOS VGA image. Install necessary packages, download SeaBIOS source and perfrorm build configuration:
$ sudo apt-get install python
$ git clone https://github.com/coreboot/seabios.git
$ cd seabios
$ make menuconfig
In a menuconfig select:
VGA ROM ---> VGA Hardware Type (qemu bochs-display support)
After that execute:
$ make
After the build resulting VGA Option ROM would be at path out/vgabios.bin. As EfiRom expects ROM files to have a *.rom extension, create a copy of a file with such extension. After that execute dump command on this file:
$ cp out/vgabios.bin out/vgabios.rom
$ EfiRom -d out/vgabios.rom
Image 1 -- Offset 0x0
ROM header contents
Signature 0xAA55
PCIR offset 0x6E00
Signature PCIR
Vendor ID 0x1234
Device ID 0x1111
Length 0x0018
Revision 0x0000
DeviceListOffset 0x00
Class Code 0x030000
Image size 0x7000
Code revision: 0x0001
MaxRuntimeImageLength 0x00
ConfigUtilityCodeHeaderOffset 0x9066
DMTFCLPEntryPointOffset 0x9066
Indicator 0x80 (last image)
Code type 0x00
This is the info similar to the one that we saw with our utility on a working QEMU system. You can see that PCI vendor/device pair is set to 1234:1111.
The main Makefile in QEMU responsible for OptionROM image creation is https://github.com/qemu/qemu/blob/master/roms/Makefile
In this Makefile you can see how:
seavgabios-%target is used for the creation of a Legacy SeaVGABIOS OptionROMefi-rom-%target is used for the creation of an OptionROM with both Legacy and UEFI iPXE code images (it even usesEfiRomutility from edk2 for this purpose)
In the previous lesson I've mentioned that PCI device can have various code images for different CPU architectures.
Check out this guide as an example https://www.workofard.com/2020/12/aarch64-option-roms-for-amd-gpus/
It explains how to add the AMD AARCH64 Gop Driver as another Code Image to the PCI graphic card OptionROM to make the graphic card work at boot time in AArch64 systems.
It uses flashrom utility to download initial PCI card Option ROM firmware and with a help of EfiRom adds AMD EFI graphic driver for AArch64 to the list of images in this OptionROM.