#Uefitool tutorial install
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Legacy bootloaders can be developed in any environment that can generate flat binary images: NASM, GCC, etc. Functions are called with a standardized, modern calling convention supported by many C compilers. UEFI applications can define their own protocols and persist them in memory for other UEFI applications to use. The behavior of each function in each protocol is defined by specification. UEFI firmware establishes many callable functions in memory, which are grouped into sets called 'protocols' and are discoverable through the System Table. Each interrupt uses a different register passing convention. These interrupts are not standardized, except by historical convention. Legacy tables (like MP tables) may not be present in memory.Ī legacy BIOS hooks a variety of interrupts which a bootloader can trigger to access system resources like disks and the screen. When UEFI firmware calls a UEFI application's entry point function, it passes a 'System Table' structure, which contains pointers to all of the system's ACPI tables, memory map, and other information relevant to an OS. It is possible that redundant tables may be present in memory (for example, the MP table in the SMBIOS contains information that's also present in the ACPI DSDT and MADT) and the bootloader can choose which to use. It uses PIO to talk to the root PCI controller and scan the PCI bus. The application can return control to the firmware, which will continue searching for another boot device or bring up a diagnostic menu.Ī legacy bootloader scans memory for structures like the EBDA, SMBIOS, and ACPI tables. Then it calls that application's main entry point. UEFI firmware loads an arbitrary sized UEFI application (a relocatable PE executable file) from a FAT partition on a GPT-partitioned boot device to some address selected at run-time. The bootloader cannot return back to BIOS. This allows UEFI firmware to be extended in a vendor-neutral way.Ī legacy BIOS loads a 512 byte flat binary blob from the MBR of the boot device into memory at physical address 7C00 and jumps to it.

UEFI firmware performs those same steps, but it also enables the A20 gate and prepares either protected mode environment with flat segmentation (for 32-bit x86 processors) or a long mode environment with identity-mapped paging (for x86-64 processors).Īdditionally, the platform initialization procedure of UEFI firmware is standardized. The bootloader must enable the A20 gate, configure a GDT and an IDT, switch to protected mode, and for x86-64 CPUs, configure paging and switch to long mode. On a legacy system, BIOS performs all the usual platform initialization (memory controller configuration, PCI bus configuration and BAR mapping, graphics card initialization, etc.), but then drops into a backwards-compatible real mode environment. The differences are in where they find the bootloader/OS, how they prepare the system before executing it, and what convenience functions they provide. In reality, both legacy motherboards and UEFI-based motherboards both include BIOS ROMs.

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Use the OVMF-blobs repo or download the RPM version, then use 7-Zip File Manager to extract the OVMF.fd file from the downloaded archive.Ī common misconception is that UEFI and BIOS are mutually exclusive.

#Uefitool tutorial install

Under Linux, you can also install these with your distro's package manager, for example: RPM packages (official TianoCore packages).

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OVMF-blobs (unofficial precompiled 32 bit and 64 bit versions, easy to use).

It might be tricky to find, so here are some alternative download links too: Otherwise for emulation and virtual machines, you'll need an OVMF.fd firmware image. You just have to enable it in the VM's preferences by clicking 'Settings' / 'Systems' / 'Enable EFI (special OSes only)' checkbox. If you choose VirtualBox for virtualization, then UEFI is already included, no need to download the image manually. 7.2 My bootloader hangs if I use user defined EFI_MEMORY_TYPE values.7.1 My UEFI application hangs/resets after about 5 minutes.1.3 Legacy bootloader or UEFI application?.