hex0.S: print hello world as a test.

amd64/Development/Makefile

@@ -3,7 +3,7 @@
 # SPDX-License-Identifier: GPL-3.0-or-later
 
 cc = clang
-cflags = -ffreestanding -MMD -mno-red-zone -std=c11 -target x86_64-unknown-windows
+cflags = -ffreestanding -MMD -mno-red-zone -std=c11 -target x86_64-unknown-windows -masm=intel
 ld = lld-link
 lflags = -subsystem:efi_application -nodefaultlib -dll
 
@@ -16,8 +16,8 @@ $(build)/%.o : %.S
 	$(cc) $(cflags) -c $< -o $@
 
 $(build)/%.efi : $(build)/%.o
-	$(ld) $(lflags) -entry:efi_main $< -out:$@
+	$(ld) $(lflags) -entry:_start $< -out:$@
 
 . PHONY : clean all
 clean:
-	rm -f $(build)
+	rm -rf $(build)

amd64/Development/hex0.S

@@ -2,13 +2,25 @@
 #
 # SPDX-License-Identifier: GPL-3.0-or-later
 
-	.text
-        .globl  efi_main
+.global _start
+.text
 
-efi_main:
-        sub    $16, %rsp
-        mov    %rdx, 8(%rsp)
-        mov    %rcx, (%rsp)
-        mov    $42, %eax
-        add    $16, %rsp
+_start:
+        mov     [ImageHandle], rcx       # ImageHandle *image
+        mov     [SystemTable], rdx       # SystemTable *system
+
+        lea     rdx, [hello]             # arg2 = "Hello World"
+        mov     rcx, [SystemTable]       # system
+        mov     rcx, [rcx+64]            # arg1 = system->out
+        call    [rcx+8]
+
+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