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| -rw-r--r-- | bootloader/README.md | 27 |
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diff --git a/bootloader/README.md b/bootloader/README.md new file mode 100644 index 0000000..4251b2f --- /dev/null +++ b/bootloader/README.md @@ -0,0 +1,27 @@ + +UEFI Bootloader +--------------- + +UEFI is a replacement to the BIOS, not only as the system firmware but also changes how the computer boots. +previously the computer would start in 16 bits mode, then jump to 32 and then to 64, all that process being the responsibility of the bootloader. +If the system is of 64 bits and the uefi firmware is also of 64 bits the system boot directly into 64 bits, meaning the bootloader binary +must be a 64 bits executable. + +It also removes old interfaces like VGA and VESA when dealing with the gpu, but in turn provides alternate ways of talking with the hardware +all those new interfaces are defined as protocols, which you need to ask for to the firmware, as such to load a file instead of parsing the disk and +reading the filesystem directly, you ask for the appropiate protocol that is able of understandding the disk and the filesystem, and then you use the API +of that protocol to load the file. + + +Steps +----- + +* firmware load the bootloader and starts executin the entry point, at this stage the bootloader is a regular program. +* clean up the screen and setup a more appropiate video mode +* allocate memory for the arguments that will be passed to the kernel +* load the kernel file form disk +* parse the ELF header of the kernel +* obtain the system memory map(is needed to exit the boot services) +* exit boot services, this destroys the uefi environment and we can no longer use anything that requires the boot services(and we can no longer return to the firmware) +* fill the the struct that will be passed to the kernel +* jump into the kernel with the information extracted from the ELF header |