From af267979164d1bb9f412705e22fc64ab00b7d899 Mon Sep 17 00:00:00 2001
From: Regia König
Date: Tue, 16 Aug 2022 16:20:17 +0200
Subject: More documentation on GNU-efi

---
 documentation/GNU-efi | 69 +++++++++++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 69 insertions(+)

diff --git a/documentation/GNU-efi b/documentation/GNU-efi
index 8dddc4a..bb22b9e 100644
--- a/documentation/GNU-efi
+++ b/documentation/GNU-efi
@@ -104,3 +104,72 @@ LINKER SCRIPT:
 	OR
 * /usr/lib/elf_x86_64_efi.lds
 
+COMPILATION:
+$ gcc
+	-Ignu-efi-dir/inc		||	set this to the efi headers directory
+
+	-fpic				||	UEFI PE executable must be relocatable
+
+	-ffreestanding			||	there's no hosted gcc environment,
+						we don't have libc
+	-fno-stack-protector		=	
+	-fno-stack-check		||	stack must be strictly used,
+					||	no additional canaries or
+					||	pre-allocated local variable
+					||	space allowed
+	-mno-red-zone			=
+
+	-fshort-wchar			||	It is very important that UEFI
+					||	uses 16bit characters
+					||	(wide-characters or wchar_t,
+					||	defined as CHAR16 in efi headers
+
+	-maccumulate-outgoing-args	|| 	function calls must include the
+					||	number of argumnets passed to the
+					|| 	functions
+
+	-c main.c -o main.o
+
+LINKING:
+$ ld 	-shared -Bsymbolic -Lgnu-efi-dir/x86_64/lib -Lgnu-efi-dir/x86_64/gnuefi \
+	-Tgnu-efi-dir/gnuefi/elf_x86_64_efi.lds \
+	gnu-efi-dir/x86_64/gnuefi/crt0-efi-x86_64.o \
+	main.o -o main.so -lgnuefi -lefi
+
+	-shared -Bsymbolic		|| tell GNU ld to create so (shared library)
+
+	-L and -T			|| Where to find the static GNU-EFI libraries
+					|| (.a) and the linker script
+
+	.o				|| it is important to specify crt0 as the
+					|| first. Should work as the last too, but
+					|| some had problems
+
+	-l				|| linking with gnuefi is a must, as that 
+					|| contains the relocation code. Linking
+					|| with efi is optional, but recommended
+
+CONVERT CHARED OBJECT TO EFI EXECUTABLE
+$ objcopy -j .text -j .sdata -j .data -j .dynamic -j .dynsym -j .rel -j .rela -j .rel.*
+	-j .rela.* -j .reloc --target efi-app-x86_64 --subsystem=10 main.so main.efi
+
+	-j				|| which sections to keep during convertion
+
+	--target efi-app-x86_64		|| tells objcop to generate a PE32+ format,
+					|| with architecture code 0x8664
+
+	--subsystem=10:			|| most important. Sets file type to UEFI
+					|| executable in the PE header
+
+Now you can copy main.efi to your EFI System Partition, and after boot run it
+from the EFI Shell. Or you can rename it to EFI\BOOT\BOOTX64.EFI and it should
+be executed automatically on boot. 
+
+
+
+
+
+
+
+
+
-- 
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