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hellowrld.asm

@@ -0,0 +1,152 @@
+format pe64 dll efi
+entry main
+
+; The UEFI calling convention is, as told in the documentation, the same
+; as the standard cdecl but for convenience (because it looks like cdecl
+; isn't that much standardized) here it is (in C-like notation):
+;
+; rax func(rcx, rdx, r8, r9, rsp+32, rsp+64, ...)
+;
+; basically the rest of arguments is passed through the stack with 32bit 
+; offset as it was designed for variadic functions
+
+; Also important fact about uefi is that uefi apps are called images.
+; for further reading I think I recommend the official uefi documentation
+; I'm not sure because maybe there might be better source
+
+; macro that saves the most important registers and calls the function 
+macro call_safe func 
+{
+    push rcx
+    push rbx
+    call func
+    pop rbx
+    pop rcx
+}
+
+
+section '.text' code executable readable
+
+include 'uefi.inc'
+
+main:
+; storing the args that the main function is called with 
+; main(*ImageHandle, *SystemTable)
+    mov             [ImgHdl], rcx
+    mov             [SysTbl], rdx
+   
+    sub             rsp, 6*8+8
+
+; storing the most used structures for faster use
+    mov             rax, [rdx + EFI_SYSTEM_TABLE.BootServices]
+    mov             [BootSrvc], rax
+    mov             rax, [rdx + EFI_SYSTEM_TABLE.ConOut]
+    mov             [Output], rax
+
+; preparing args and calling 
+; ConOut.SetAttribute(Output, BG_CLR | FG_CLR)
+    mov             rax, EFI_BACKGROUND_BLACK or EFI_GREEN
+ 
+    mov             rcx, [Output]
+    call_safe       [rcx + SIMPLE_TEXT_OUTPUT_INTERFACE.SetAttribute]
+
+; clearing the screen
+; ConOut.ClearScreen(ConOut)
+    mov             rcx, [Output]            
+    call_safe       [rcx + SIMPLE_TEXT_OUTPUT_INTERFACE.ClearScreen]
+
+; printing the initial message to indicate 
+; that the bootloader started successfully
+    mov             rdx, BootMsg
+    call            print
+
+
+; TODO: Get and store framebuffer
+
+; Getting the memory map is kind of harder (not in this case), normally 
+; you would need to call the function two times to get the buffer size 
+; then allocate it (+ some padding because it will expand because of the 
+; allocation) and then call it again, but as I'm storing it somewhere 
+; in memory, I'm not using for now, I can just call it two times without 
+; the allocation.
+; BootServices.GetMemoryMap(
+;                           *MemMapSize,
+;                           *MemMapBuffer,
+;                           *MemMapKey,
+;                           *MemMapDescSize,
+;                           *MemMapDescVer)
+.GetMemMap:
+    lea             rcx, [MemMapSize]
+    mov             rdx, [MemMapBuff]
+    lea             r8,  [MemMapKey]
+    lea             r9,  [MemMapDescSize]
+; notice the last argument is moved to r10 and then "pushed" to the stack
+; with 32bit offset
+    lea             r10, [MemMapDescVer]
+    mov             [rsp+32], r10
+
+    call            [BootSrvc + EFI_BOOT_SERVICES_TABLE.GetMemoryMap]
+
+; if it returns buffer too small run the function again as it filled out
+; the needed buffer length    
+    cmp              al, EFI_BUFFER_TOO_SMALL
+    je               .GetMemMap
+
+; if it returned something else it maybe a problem possible TODO: proper 
+; error handling for now it just puts out error and exits with non-zero code
+    cmp              rax, EFI_SUCCESS
+    jne              .error
+
+; print a message saying that we didn't f**k up yet...
+    mov             rdx, OKMsg
+    call            print
+
+; preparing args and calling
+; BootServices.ExitBootServices(*ImegeHandle, *MemMapKey) 
+    mov             rcx, [ImgHdl]
+    mov             rdx, [MemMapKey]
+
+    call_safe       [BootSrvc + EFI_BOOT_SERVICES_TABLE.ExitBootServices]
+
+    cmp             rax, EFI_SUCCESS
+    jne             .error
+
+    mov             eax, EFI_SUCCESS 
+    jmp             .exit
+
+.error:
+    mov             rdx, ErrMsg
+    call            print
+    mov             eax, 1
+    
+.exit: 
+    ret
+
+; print the string in rdx
+print:             
+    mov             rcx, [Output]
+    call_safe       [rcx + SIMPLE_TEXT_OUTPUT_INTERFACE.OutputString]
+    ret
+    
+; Should not be reachable
+    hlt
+    jmp $
+
+section '.data' data readable writeable
+
+ImgHdl                                  dq ?
+SysTbl                                  dq ?
+BootSrvc                                dq ?
+Output                                  dq ?
+
+MemMapSize                              dq 32768 
+MemMapKey                               dq ?
+MemMapDescSize                          dq ?
+MemMapDescVer                           dq ?
+MemMapBuff                              dq 0x220000 
+
+BootMsg                                 du '[BOOT]: Booting the system...',13,10,0
+ErrMsg                                 du '[BOOT]: There was an error :(',13,10,0
+OKMsg                                 du '[BOOT]: Everything is OK :), for now...',13,10,0
+
+section '.reloc' fixups data discardable