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UEFI Programming with FASM
As an extra, I will also demonstrate same Hello World example in assembly (using FASM, that currently has experimental UEFI support since version 1.67.28):
First we need some to create simple UEFI headers (efi.inc):
;for 32/64 portability and automatic natural align in structure definitions
struc int8 {
. db ?
}
struc int16 {
align 2
. dw ?
}
struc int32 {
align 4
. dd ?
}
struc int64 {
align 8
. dq ?
}
struc intn {
align 8
. dq ?
}
struc dptr {
align 8
. dq ?
}
;symbols
EFIERR = 0x8000000000000000
EFI_SUCCESS = 0
EFI_LOAD_ERROR = EFIERR or 1
EFI_INVALID_PARAMETER = EFIERR or 2
EFI_UNSUPPORTED = EFIERR or 3
EFI_BAD_BUFFER_SIZE = EFIERR or 4
EFI_BUFFER_TOO_SMALL = EFIERR or 5
EFI_NOT_READY = EFIERR or 6
EFI_DEVICE_ERROR = EFIERR or 7
EFI_WRITE_PROTECTED = EFIERR or 8
EFI_OUT_OF_RESOURCES = EFIERR or 9
EFI_VOLUME_CORRUPTED = EFIERR or 10
EFI_VOLUME_FULL = EFIERR or 11
EFI_NO_MEDIA = EFIERR or 12
EFI_MEDIA_CHANGED = EFIERR or 13
EFI_NOT_FOUND = EFIERR or 14
EFI_ACCESS_DENIED = EFIERR or 15
EFI_NO_RESPONSE = EFIERR or 16
EFI_NO_MAPPING = EFIERR or 17
EFI_TIMEOUT = EFIERR or 18
EFI_NOT_STARTED = EFIERR or 19
EFI_ALREADY_STARTED = EFIERR or 20
EFI_ABORTED = EFIERR or 21
EFI_ICMP_ERROR = EFIERR or 22
EFI_TFTP_ERROR = EFIERR or 23
EFI_PROTOCOL_ERROR = EFIERR or 24
;helper macro for definition of relative structure member offsets
macro struct name
{
virtual at 0
name name
end virtual
}
;structures
struc EFI_TABLE_HEADER {
.Signature int64
.Revision int32
.HeaderSize int32
.CRC32 int32
.Reserved int32
}
struct EFI_TABLE_HEADER
struc EFI_SYSTEM_TABLE {
.Hdr EFI_TABLE_HEADER
.FirmwareVendor dptr
.FirmwareRevision int32
.ConsoleInHandle dptr
.ConIn dptr
.ConsoleOutHandle dptr
.ConOut dptr
.StandardErrorHandle dptr
.StdErr dptr
.RuntimeServices dptr
.BootServices dptr
.NumberOfTableEntries intn
.ConfigurationTable dptr
}
struct EFI_SYSTEM_TABLE
struc SIMPLE_TEXT_OUTPUT_INTERFACE {
.Reset dptr
.OutputString dptr
.TestString dptr
.QueryMode dptr
.SetMode dptr
.SetAttribute dptr
.ClearScreen dptr
.SetCursorPosition dptr
.EnableCursor dptr
.Mode dptr
}
struct SIMPLE_TEXT_OUTPUT_INTERFACE
And here is the assembly code itself (hello.asm):
format pe64 dll efi
entry main
section '.text' code executable readable
include 'efi.inc'
main:
sub rsp, 4*8 ; reserve space for 4 arguments
mov [Handle], rcx ; ImageHandle
mov [SystemTable], rdx ; pointer to SystemTable
lea rdx, [_hello]
mov rcx, [SystemTable]
mov rcx, [rcx + EFI_SYSTEM_TABLE.ConOut]
call [rcx + SIMPLE_TEXT_OUTPUT_INTERFACE.OutputString]
add rsp, 4*8
mov eax, EFI_SUCCESS
retn
section '.data' data readable writeable
Handle dq ?
SystemTable dq ?
_hello du 'Hello World',13,10,'(From EFI app written in FASM)',13,10,0
section '.reloc' fixups data discardable
Compile and link it with fasm.exe hello_world.asm.
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