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. The A20 gate is enabled as well.Īdditionally, the platform initialization procedure of UEFI firmware is standardized. UEFI firmware performs those same steps, but also prepares a protected mode environment with flat segmentation and for x86-64 CPUs, a long mode environment with identity-mapped paging. 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. Legacy system mac emulator code#The differences between legacy BIOS firmware and UEFI BIOS firmware are where they find that code, how they prepare the system before jumping to it, and what convenience functions they provide for the code to call while running. In reality, both legacy motherboards and UEFI-based motherboards come with BIOS ROMs, which contain firmware that performs the initial power-on configuration of the system before loading some third-party code into memory and jumping to it. Legacy system mac emulator download#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 is a replacement for BIOS. Legacy system mac emulator install#Under Linux, you can also install these with your distro's package manager, for example:
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