From d0e6bdb758d2424ff9efcc1d83a662a6f2b5fafd Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Andrius=20=C5=A0tikonas?= <andrius@stikonas.eu>
Date: Mon, 11 Jul 2022 01:22:34 +0100
Subject: [PATCH] hex0.S: implement open_protocol function.

---
 amd64/Development/hex0.S | 41 ++++++++++++++++++++++++++++++----------
 1 file changed, 31 insertions(+), 10 deletions(-)

diff --git a/amd64/Development/hex0.S b/amd64/Development/hex0.S
index 4a73119..d6c9d27 100644
--- a/amd64/Development/hex0.S
+++ b/amd64/Development/hex0.S
@@ -2,25 +2,46 @@
 #
 # SPDX-License-Identifier: GPL-3.0-or-later
 
+# Calling convention:
+# First four arguments are passed via registers but we need to leave stack space
+
 .global _start
 .text
 
 _start:
-        mov     [ImageHandle], rcx       # ImageHandle *image
-        mov     [SystemTable], rdx       # SystemTable *system
+        sub  rsp, 64
+        mov  [ImageHandle], rcx            # ImageHandle *image_handle
+        mov  rax, [rdx+96]                 # system->boot
+        mov  [SystemBoot], rax             # save system->boot
 
-        lea     rdx, [hello]             # arg2 = "Hello World"
-        mov     rcx, [SystemTable]       # system
-        mov     rcx, [rcx+64]            # arg1 = system->out
-        call    [rcx+8]
+        # Open Loaded Image protocol
+                                           # arg1 = ImageHandle
+        mov  rdx, [LOADED_IMAGE_PROTOCOL]  # EFI_LOADED_IMAGE_PROTOCOL_GUID (first 64 bits)
+        mov  [rsp+48], rdx                 # save onto stack
+        mov  rdx, [LOADED_IMAGE_PROTOCOL+8]# EFI_LOADED_IMAGE_PROTOCOL_GUID (last 64 bits)
+        mov  [rsp+56], rdx                 # save onto stack
+        lea  rdx, [rsp+48]                 # arg2 = &EFI_LOADED_IMAGE_PROTOCOL_GUID
+                                           # arg3 = &image
+        mov  r9, rcx                       # arg4 = image_handle
+        mov  qword ptr [rsp+32], 0         # arg5 = NULL
+        mov  qword ptr [rsp+40], 1         # arg6 = EFI_OPEN_PROTOCOL_BY_HANDLE_PROTOCOL
+
+        call [rax+280]                     # system->boot->open_protocol();
+        add  rsp, 64
+
+        # Command line args
 
 Done:
-        mov    rax, 0                   # rax = 0
         ret
 
 .data
 
-hello: .asciz "H\0e\0l\0l\0o\0 \0w\0o\0r\0l\0d\0!\0\n\0\r\0\0"
-
 ImageHandle: .quad 0
-SystemTable: .quad 0
+SystemBoot: .quad 0
+
+# Protocol GUIDs
+LOADED_IMAGE_PROTOCOL:
+.long  0x5b1b31a1
+.short 0x9562
+.short 0x11d2
+.byte 0x8e, 0x3f, 0x00, 0xa0, 0xc9, 0x69, 0x72, 0x3b