cpu/x86/64bit: Generate static page tables from an assembly file

This removes the need for a tool to generate simple identity pages.
Future patches will link this page table directly into the stages on
some platforms so having an assembly file makes a lot of sense.

This also optimizes the size of the page of each 4K page by placing
the PDPE_table below the PDE.

Change-Id: Ia1e31b701a2584268c85d327bf139953213899e3
Signed-off-by: Arthur Heymans <arthur@aheymans.xyz>
Reviewed-on: https://review.coreboot.org/c/coreboot/+/63725
Tested-by: build bot (Jenkins) <no-reply@coreboot.org>
Reviewed-by: Raul Rangel <rrangel@chromium.org>

src/cpu/x86/64bit/Makefile.inc

@@ -5,3 +5,15 @@ endif
 romstage-y += mode_switch.S
 postcar-y += mode_switch.S
 ramstage-y += mode_switch.S
+
+# Add --defsym=_start=0 to suppress a linker warning.
+$(objcbfs)/pt: $(dir)/pt.S
+	$(CC_bootblock) $(CFLAGS_bootblock) $(CPPFLAGS_bootblock) -o $@.tmp $< -Wl,--section-start=.rodata=$(CONFIG_ARCH_X86_64_PGTBL_LOC),--defsym=_start=0
+	$(OBJCOPY_ramstage) -Obinary -j .rodata $@.tmp $@
+	rm $@.tmp
+
+cbfs-files-y += pagetables
+pagetables-file := $(objcbfs)/pt
+pagetables-type := raw
+pagetables-compression := none
+pagetables-COREBOOT-position := $(CONFIG_ARCH_X86_64_PGTBL_LOC)

src/cpu/x86/64bit/pt.S

@@ -0,0 +1,35 @@
+/* SPDX-License-Identifier: GPL-2.0-only */
+
+/*
+ * For reference see "AMD64 Architecture Programmer's Manual Volume 2",
+ * Document 24593-Rev. 3.31-July 2019 Chapter 5.3.4
+ *
+ * Page table attributes: WB, User+Supervisor, Present, Writeable, Accessed, Dirty
+ */
+
+.section .rodata
+#define _PRES (1ULL << 0)
+#define _RW   (1ULL << 1)
+#define _US   (1ULL << 2)
+#define _A    (1ULL << 5)
+#define _D    (1ULL << 6)
+#define _PS   (1ULL << 7)
+#define _GEN_DIR(a) (_PRES + _RW + _US + _A + (a))
+#define _GEN_PAGE(a) (_PRES + _RW + _US + _PS + _A +  _D + (a))
+
+.global PM4LE
+.align 32
+PM4LE:
+.quad _GEN_DIR(PDPE_table)
+
+.align 4096
+PDE_tables: /* identity map 2MiB pages */
+.rept 2048
+.quad _GEN_PAGE(0x200000 * ((. - PDE_tables) >> 3))
+.endr
+
+.align 4096
+PDPE_table: /* Point to PDE */
+.rept 4
+.quad _GEN_DIR(PDE_tables + 4096 * ((. - PDPE_table) >> 3))
+.endr