[efi] Add EFI image format and basic runtime environment

We have EFI APIs for CPU I/O, PCI I/O, timers, console I/O, user
access and user memory allocation.

EFI executables are created using the vanilla GNU toolchain, with the
EXE header handcrafted in assembly and relocations generated by a
custom efilink utility.

src/arch/i386/scripts/efi.lds

@@ -0,0 +1,174 @@
+/* -*- sh -*- */
+
+/*
+ * Linker script for EFI images
+ *
+ */
+
+EXTERN ( efi_entry )
+
+SECTIONS {
+
+    /* The file starts at a virtual address of zero, and sections are
+     * contiguous.  Each section is aligned to at least _max_align,
+     * which defaults to 32.  Load addresses are equal to virtual
+     * addresses.
+     */
+
+    . = 0;
+    PROVIDE ( _max_align = 32 );
+
+    /*
+     * The prefix
+     *
+     */
+
+    .prefix : AT ( _prefix_lma ) {
+	_prefix = .;
+	*(.prefix)
+	*(.prefix.*)
+	_mprefix = .;
+    } .prefix_bss (NOLOAD) : {
+	_eprefix = .;
+    }
+    _prefix_filesz	= ABSOLUTE ( _mprefix - _prefix );
+    _prefix_memsz	= ABSOLUTE ( _eprefix - _prefix );
+
+    /*
+     * The text section
+     *
+     */
+
+    . = ALIGN ( _max_align );
+    .text : AT ( _text_lma ) {
+	_text = .;
+	*(.text)
+	*(.text.*)
+	_mtext = .;
+    } .text_bss (NOLOAD) : {
+	_etext = .;
+    }
+    _text_filesz	= ABSOLUTE ( _mtext - _text );
+    _text_memsz		= ABSOLUTE ( _etext - _text );
+
+    /*
+     * The rodata section
+     *
+     */
+
+    . = ALIGN ( _max_align );
+    .rodata : AT ( _rodata_lma ) {
+	_rodata = .;
+	*(.rodata)
+	*(.rodata.*)
+	_mrodata = .;
+    } .rodata_bss (NOLOAD) : {
+	_erodata = .;
+    }
+    _rodata_filesz	= ABSOLUTE ( _mrodata - _rodata );
+    _rodata_memsz	= ABSOLUTE ( _erodata - _rodata );
+
+    /*
+     * The data section
+     *
+     */
+
+    . = ALIGN ( _max_align );
+    .data : AT ( _data_lma ) {
+	_data = .;
+	*(.data)
+	*(.data.*)
+	*(SORT(.tbl.*))		/* Various tables.  See include/tables.h */
+	/* EFI seems to not support proper bss sections */
+	*(.bss)
+	*(.bss.*)
+	*(COMMON)
+	*(.stack)
+	*(.stack.*)
+	_mdata = .;
+    } .data_bss (NOLOAD) : {
+	_edata = .;
+    }
+    _data_filesz	= ABSOLUTE ( _mdata - _data );
+    _data_memsz		= ABSOLUTE ( _edata - _data );
+
+    /*
+     * The bss section
+     *
+     */
+
+    . = ALIGN ( _max_align );
+    .bss : AT ( _bss_lma ) {
+	_bss = .;
+	/* EFI seems to not support proper bss sections */
+	_mbss = .;
+    } .bss_bss (NOLOAD) : {
+	_ebss = .;
+    }
+    _bss_filesz		= ABSOLUTE ( _mbss - _bss );
+    _bss_memsz		= ABSOLUTE ( _ebss - _bss );
+
+    /*
+     * The reloc section
+     *
+     */
+
+    . = ALIGN ( _max_align );
+    .reloc : AT ( _reloc_lma ) {
+	_reloc = .;
+	/* Provide some dummy contents to force ld to include this
+	 * section.  It will be created by the efilink utility.
+	 */
+	. += 1;
+	_mreloc = .;
+    } .reloc_bss (NOLOAD) : {
+	_ereloc = .;
+    }
+    _reloc_filesz	= ABSOLUTE ( _mreloc - _reloc );
+    _reloc_memsz	= ABSOLUTE ( _ereloc - _reloc );
+
+    _filesz		= ABSOLUTE ( . );
+
+    /*
+     * Weak symbols that need zero values if not otherwise defined
+     *
+     */
+
+    .weak 0x0 : {
+	_weak = .;
+	*(.weak)
+	_eweak = .;
+    }
+    _assert = ASSERT ( ( _weak == _eweak ), ".weak is non-zero length" );
+
+    /*
+     * Dispose of the comment and note sections to make the link map
+     * easier to read
+     *
+     */
+
+    /DISCARD/ : {
+	*(.comment)
+	*(.note)
+    }
+
+    /*
+     * Load address calculations.
+     *
+     */
+
+    _prefix_lma		= ABSOLUTE ( _prefix );
+    _text_lma		= ABSOLUTE ( _text );
+    _rodata_lma		= ABSOLUTE ( _rodata );
+    _data_lma		= ABSOLUTE ( _data );
+    _bss_lma		= ABSOLUTE ( _bss );
+    _reloc_lma		= ABSOLUTE ( _reloc );
+
+    /*
+     * Load addresses required by the prefix
+     *
+     */
+    efi_entry_lma	= ABSOLUTE ( efi_entry );
+    debugdir_lma	= ABSOLUTE ( debugdir );
+    codeview_rsds_lma	= ABSOLUTE ( codeview_rsds );
+}