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>

Documentation/arch/x86/index.md

@@ -26,9 +26,7 @@ In order to add support for x86_64 the following assumptions were made:
 * A stage can install new page tables in RAM
 
 ## Page tables
-Page tables are generated by a tool in `util/pgtblgen/pgtblgen`. It writes
+A `pagetables` cbfs file is generated based on an assembly file.
-the page tables to a file which is then included into the CBFS as file called
-`pagetables`.
 
 To generate the static page tables it must know the physical address where to
 place the file.

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

util/pgtblgen/Makefile.inc

@@ -1,19 +0,0 @@
-ifeq ($(CONFIG_ARCH_BOOTBLOCK_X86_64),y)
-
-PGTBLGEN:= $(obj)/pgtblgen
-
-cbfs-files-y += pagetables
-pagetables-file := $(obj)/mainboard/$(MAINBOARDDIR)/pagetables
-pagetables-type := raw
-pagetables-compression := none
-pagetables-COREBOOT-position := $(CONFIG_ARCH_X86_64_PGTBL_LOC)
-
-$(obj)/mainboard/$(MAINBOARDDIR)/pagetables: $(PGTBLGEN) $(obj)/config.h
-	printf "    TOOL       Creating page tables\n"
-	$(PGTBLGEN) -b $(CONFIG_ARCH_X86_64_PGTBL_LOC) -a x86_64 -o $@
-
-$(PGTBLGEN): util/pgtblgen/pgtblgen.c
-	printf "    MAKE       Creating PGTBLGEN tool\n"
-	$(HOSTCC) -std=c99 $< -I$(obj) -o $@
-
-endif

util/pgtblgen/description.md

@@ -1 +0,0 @@
-Generates page tables based on fixed physical address. `C`

util/pgtblgen/pgtblgen.c

@@ -1,158 +0,0 @@
-/* SPDX-License-Identifier: GPL-2.0-only */
-
-#include <stdio.h>
-#include <stdlib.h>
-#include <unistd.h>
-#include <string.h>
-#include <sys/types.h>
-#include <sys/stat.h>
-#include <fcntl.h>
-#include <errno.h>
-#include <inttypes.h>
-#include <getopt.h>
-
-static void usage(char *argv[])
-{
-	printf("usage: %s -b <addr> -a <arch> -o <file>\n", argv[0]);
-	printf("  -a\t architecture. Supported: x86_64\n");
-	printf("  -b\t base address\n");
-	printf("  -o\t the file to write to\n");
-	printf("  -h\t show this help text\n");
-}
-
-/*
- * For reference see "AMD64 ArchitectureProgrammer'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
- */
-#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))
-
-/*
- * Generate x86_64 page tables.
- * The page tables needs to be placed at @base_address, and identity map
- * the first @size_gib GiB of physical memory.
- */
-static int gen_pgtbl_x86_64(const uint64_t base_address,
-			    const size_t size_gib,
-			    void **out_buf,
-			    size_t *out_size)
-{
-	uint64_t *entry;
-
-	if (!out_size || !out_buf)
-		return 1;
-
-	*out_size = (size_gib + 2) * 4096;
-	*out_buf = malloc(*out_size);
-	if (!*out_buf)
-		return 1;
-
-	memset(*out_buf, 0, *out_size);
-	entry = (uint64_t *)*out_buf;
-
-	/* Generate one PM4LE entry - point to PDPE */
-	entry[0] = _GEN_DIR(base_address + 4096);
-	entry += 512;
-
-	/* PDPE table - point to PDE */
-	for (size_t i = 0; i < size_gib; i++)
-		entry[i] = _GEN_DIR(base_address + 4096 * (i + 2));
-	entry += 512;
-
-	/* PDE tables - identity map 2MiB pages */
-	for (size_t g = 0; g < size_gib; g++) {
-		for (size_t i = 0; i < 512; i++) {
-			uint64_t addr = ((1ULL << (12 + 9)) * i) | ((1ULL << (12 + 9 + 9)) * g);
-			entry[i] = _GEN_PAGE(addr);
-		}
-		entry += 512;
-	}
-
-	return 0;
-}
-
-int main(int argc, char *argv[])
-{
-	int ret = 1;
-	uint64_t base_address = 0;
-	char *filename = NULL;
-	char *arch = NULL;
-	void *buf = NULL;
-	size_t buf_size = 0;
-	int c;
-
-	while ((c = getopt(argc, argv, "ho:a:b:")) != -1)
-		switch (c) {
-		case '?': /* falltrough */
-		case 'h':
-			usage(argv);
-			return 0;
-		case 'o':
-			filename = optarg;
-			break;
-		case 'a':
-			arch = optarg;
-			break;
-		case 'b':
-			base_address = strtoull(optarg, NULL, 0);
-			break;
-		default:
-			break;
-		}
-
-	if (!filename) {
-		fprintf(stderr, "E: Missing filename.\n");
-		goto done;
-	}
-	if (!arch) {
-		fprintf(stderr, "E: Missing architecture.\n");
-		goto done;
-	} else if (strcmp(arch, "x86_64") != 0) {
-		fprintf(stderr, "E: Unsupported architecture.\n");
-		goto done;
-	}
-	if (base_address & 4095) {
-		fprintf(stderr, "E: Base address not 4 KiB aligned\n");
-		goto done;
-	}
-
-	/* FIXME: Identity map 4GiB for now, increase if necessary */
-	if (strcmp(arch, "x86_64") == 0)
-		ret = gen_pgtbl_x86_64(base_address, 4, &buf, &buf_size);
-
-	if (ret) {
-		fprintf(stderr, "Failed to generate page tables\n");
-		goto done;
-	}
-
-	// write the table
-	FILE *fd = fopen(filename, "wb");
-	if (!fd) {
-		fprintf(stderr, "%s open failed: %s\n", filename, strerror(errno));
-		goto done;
-	}
-
-	if (fwrite(buf, 1, buf_size, fd) != buf_size) {
-		fprintf(stderr, "%s write failed: %s\n", filename, strerror(errno));
-		fclose(fd);
-		goto done;
-	}
-
-	if (fclose(fd)) {
-		fprintf(stderr, "%s close failed: %s\n", filename, strerror(errno));
-		goto done;
-	}
-
-	ret = 0;
-done:
-	free(buf);
-	return ret;
-}