[Qemu-devel] [PATCH 3/4] Multiboot support v3

[Alexander Graf <agraf@suse.de>]

This patch implements support for Multiboot on x86 for -kernel.
Multiboot is a "new" approach to get rid of different bootloaders, providing
a unified interface for the kernel. It supports command line options and
kernel modules.

The two probably best known projects using multiboot are Xen and GNU Hurd.

This implementation should be mostly feature-complete. It is missing VBE
extensions, but as no system uses them currently it does not really hurt.

To use multiboot, specify the kernel as -kernel option. Modules should be given
as -initrd options, seperated by a comma (,). -append also works.

Please bear in mind that grub also does gzip decompression, which qemu does
not do yet. To run existing images, please ungzip them first.

The guest multiboot loader code is implemented as option rom using int 19.
Parts of the work are based on efforts by Rene Rebe, who originally ported
my code to int 19.

Signed-off-by: Alexander Graf <agraf@suse.de>

---

v2 uses fw_cfg directly instead of env->fw_cfg
v3 changes:
 - kvm compatibility (thanks gleb!)
 - reformat if and for (avi)
---
 hw/pc.c                       |  225 +++++++++++++++++++++++++++++++++++++++--
 pc-bios/multiboot/multiboot.S |  209 ++++++++++++++++++++++++++++++++++++++
 2 files changed, 426 insertions(+), 8 deletions(-)
 create mode 100644 pc-bios/multiboot/multiboot.S

diff --git a/hw/pc.c b/hw/pc.c
index debde9d..38b847e 100644
--- a/hw/pc.c
+++ b/hw/pc.c
@@ -40,6 +40,9 @@
 /* output Bochs bios info messages */
 //#define DEBUG_BIOS
 
+/* Show multiboot debug output */
+//#define DEBUG_MULTIBOOT
+
 #define BIOS_FILENAME "bios.bin"
 #define VGABIOS_FILENAME "vgabios.bin"
 #define VGABIOS_CIRRUS_FILENAME "vgabios-cirrus.bin"
@@ -596,7 +599,197 @@ static long get_file_size(FILE *f)
     return size;
 }
 
-static void load_linux(target_phys_addr_t option_rom,
+static int load_multiboot(void *fw_cfg,
+                          FILE *f,
+                          const char *kernel_filename,
+                          const char *initrd_filename,
+                          const char *kernel_cmdline,
+                          uint8_t *header)
+{
+    int i, is_multiboot = 0;
+    uint32_t flags = 0;
+    uint32_t mh_entry_addr;
+    uint32_t mh_load_addr;
+    uint32_t mb_kernel_size;
+    uint32_t mb_bootinfo = 0x90500;
+    uint32_t mmap_addr = 0x90000;
+
+    /* Ok, let's see if it is a multiboot image.
+       The header is 12x32bit long, so the latest entry may be 8192 - 48. */
+    for (i = 0; i < (8192 - 48); i += 4) {
+        if (ldl_p(header+i) == 0x1BADB002) {
+            uint32_t checksum = ldl_p(header+i+8);
+            flags = ldl_p(header+i+4);
+            checksum += flags;
+            checksum += (uint32_t)0x1BADB002;
+            if (!checksum) {
+                is_multiboot = 1;
+                break;
+            }
+        }
+    }
+
+    if (!is_multiboot)
+        return 0; /* no multiboot */
+
+#ifdef DEBUG_MULTIBOOT
+    fprintf(stderr, "qemu: I believe we found a multiboot image!\n");
+#endif
+
+    if (flags & 0x00000004) { /* MULTIBOOT_HEADER_HAS_VBE */
+        fprintf(stderr, "qemu: multiboot knows VBE. we don't.\n");
+    }
+    if (!(flags & 0x00010000)) { /* MULTIBOOT_HEADER_HAS_ADDR */
+        uint64_t elf_entry;
+        int kernel_size;
+        fclose(f);
+        kernel_size = load_elf(kernel_filename, 0, &elf_entry, NULL, NULL);
+        if (kernel_size < 0) {
+            fprintf(stderr, "Error while loading elf kernel\n");
+            exit(1);
+        }
+        mh_load_addr = mh_entry_addr = elf_entry;
+        mb_kernel_size = kernel_size;
+
+#ifdef DEBUG_MULTIBOOT
+        fprintf(stderr, "qemu: loading multiboot-elf kernel (%#x bytes) with entry %#zx\n",
+                mb_kernel_size, (size_t)mh_entry_addr);
+#endif
+    } else {
+        /* Valid if mh_flags sets MULTIBOOT_HEADER_HAS_ADDR. */
+        uint32_t mh_header_addr = ldl_p(header+i+12);
+        mh_load_addr = ldl_p(header+i+16);
+#ifdef DEBUG_MULTIBOOT
+        uint32_t mh_load_end_addr = ldl_p(header+i+20);
+        uint32_t mh_bss_end_addr = ldl_p(header+i+24);
+#endif
+        uint32_t mb_kernel_text_offset = i - (mh_header_addr - mh_load_addr);
+
+        mh_entry_addr = ldl_p(header+i+28);
+        mb_kernel_size = get_file_size(f) - mb_kernel_text_offset;
+
+        /* Valid if mh_flags sets MULTIBOOT_HEADER_HAS_VBE.
+        uint32_t mh_mode_type = ldl_p(header+i+32);
+        uint32_t mh_width = ldl_p(header+i+36);
+        uint32_t mh_height = ldl_p(header+i+40);
+        uint32_t mh_depth = ldl_p(header+i+44); */
+
+#ifdef DEBUG_MULTIBOOT
+        fprintf(stderr, "multiboot: mh_header_addr = %#x\n", mh_header_addr);
+        fprintf(stderr, "multiboot: mh_load_addr = %#x\n", mh_load_addr);
+        fprintf(stderr, "multiboot: mh_load_end_addr = %#x\n", mh_load_end_addr);
+        fprintf(stderr, "multiboot: mh_bss_end_addr = %#x\n", mh_bss_end_addr);
+#endif
+
+        fseek(f, mb_kernel_text_offset, SEEK_SET);
+
+#ifdef DEBUG_MULTIBOOT
+        fprintf(stderr, "qemu: loading multiboot kernel (%#x bytes) at %#x\n",
+                mb_kernel_size, mh_load_addr);
+#endif
+
+        if (!fread_targphys_ok(mh_load_addr, mb_kernel_size, f)) {
+            fprintf(stderr, "qemu: read error on multiboot kernel '%s' (%#x)\n",
+                    kernel_filename, mb_kernel_size);
+            exit(1);
+        }
+        fclose(f);
+    }
+
+
+    /* load modules */
+    stl_phys(mb_bootinfo + 20, 0x0); /* mods_count */
+    if (initrd_filename) {
+        uint32_t mb_mod_info = mb_bootinfo + 0x100;
+        uint32_t mb_mod_cmdline = mb_bootinfo + 0x300;
+        uint32_t mb_mod_start = mh_load_addr;
+        uint32_t mb_mod_length = mb_kernel_size;
+        char *next_initrd;
+        char *next_space;
+        int mb_mod_count = 0;
+
+        do {
+            next_initrd = strchr(initrd_filename, ',');
+            if (next_initrd)
+                *next_initrd = '\0';
+            /* if a space comes after the module filename, treat everything
+               after that as parameters */
+            cpu_physical_memory_write(mb_mod_cmdline, (uint8_t*)initrd_filename,
+                                      strlen(initrd_filename) + 1);
+            stl_phys(mb_mod_info + 8, mb_mod_cmdline); /* string */
+            mb_mod_cmdline += strlen(initrd_filename) + 1;
+            if ((next_space = strchr(initrd_filename, ' ')))
+                *next_space = '\0';
+#ifdef DEBUG_MULTIBOOT
+	     printf("multiboot loading module: %s\n", initrd_filename);
+#endif
+            f = fopen(initrd_filename, "rb");
+            if (f) {
+                mb_mod_start = (mb_mod_start + mb_mod_length + (TARGET_PAGE_SIZE - 1))
+                             & (TARGET_PAGE_MASK);
+                mb_mod_length = get_file_size(f);
+
+                if (!fread_targphys_ok(mb_mod_start, mb_mod_length, f)) {
+                    fprintf(stderr, "qemu: read error on multiboot module '%s' (%#x)\n",
+                            initrd_filename, mb_mod_length);
+                    exit(1);
+                }
+
+                mb_mod_count++;
+                stl_phys(mb_mod_info + 0, mb_mod_start);
+                stl_phys(mb_mod_info + 4, mb_mod_start + mb_mod_length);
+#ifdef DEBUG_MULTIBOOT
+                printf("mod_start: %#x\nmod_end:   %#x\n", mb_mod_start,
+                       mb_mod_start + mb_mod_length);
+#endif
+                stl_phys(mb_mod_info + 12, 0x0); /* reserved */
+            }
+            initrd_filename = next_initrd+1;
+            mb_mod_info += 16;
+        } while (next_initrd);
+        stl_phys(mb_bootinfo + 20, mb_mod_count); /* mods_count */
+        stl_phys(mb_bootinfo + 24, mb_bootinfo + 0x100); /* mods_addr */
+    }
+
+    /* Commandline support */
+    stl_phys(mb_bootinfo + 16, mb_bootinfo + 0x200);
+    cpu_physical_memory_write(mb_bootinfo + 0x200, (uint8_t*)kernel_cmdline,
+                              strlen(kernel_cmdline) + 1);
+
+    /* the kernel is where we want it to be now */
+
+#define MULTIBOOT_FLAGS_MEMORY (1 << 0)
+#define MULTIBOOT_FLAGS_BOOT_DEVICE (1 << 1)
+#define MULTIBOOT_FLAGS_CMDLINE (1 << 2)
+#define MULTIBOOT_FLAGS_MODULES (1 << 3)
+#define MULTIBOOT_FLAGS_MMAP (1 << 6)
+    stl_phys(mb_bootinfo, MULTIBOOT_FLAGS_MEMORY
+                        | MULTIBOOT_FLAGS_BOOT_DEVICE
+                        | MULTIBOOT_FLAGS_CMDLINE
+                        | MULTIBOOT_FLAGS_MODULES
+                        | MULTIBOOT_FLAGS_MMAP);
+    stl_phys(mb_bootinfo + 4, 640); /* mem_lower */
+    stl_phys(mb_bootinfo + 8, ram_size / 1024); /* mem_upper */
+    stl_phys(mb_bootinfo + 12, 0x8001ffff); /* XXX: use the -boot switch? */
+    stl_phys(mb_bootinfo + 48, mmap_addr); /* mmap_addr */
+
+#ifdef DEBUG_MULTIBOOT
+    fprintf(stderr, "multiboot: mh_entry_addr = %#x\n", mh_entry_addr);
+#endif
+
+    /* Pass variables to option rom */
+    fw_cfg_add_i32(fw_cfg, FW_CFG_KERNEL_ADDR, mh_entry_addr);
+    fw_cfg_add_i32(fw_cfg, FW_CFG_INITRD_ADDR, mb_bootinfo);
+    fw_cfg_add_i32(fw_cfg, FW_CFG_INITRD_SIZE, mmap_addr);
+
+    option_rom[nb_option_roms] = "multiboot.bin";
+    nb_option_roms++;
+
+    return 1; /* yes, we are multiboot */
+}
+
+static void load_linux(void *fw_cfg,
+                       target_phys_addr_t option_rom,
                        const char *kernel_filename,
 		       const char *initrd_filename,
 		       const char *kernel_cmdline,
@@ -608,7 +801,7 @@ static void load_linux(target_phys_addr_t option_rom,
     uint16_t real_seg;
     int setup_size, kernel_size, initrd_size = 0, cmdline_size;
     uint32_t initrd_max;
-    uint8_t header[1024];
+    uint8_t header[8192];
     target_phys_addr_t real_addr, prot_addr, cmdline_addr, initrd_addr = 0;
     FILE *f, *fi;
 
@@ -618,7 +811,8 @@ static void load_linux(target_phys_addr_t option_rom,
     /* load the kernel header */
     f = fopen(kernel_filename, "rb");
     if (!f || !(kernel_size = get_file_size(f)) ||
-	fread(header, 1, 1024, f) != 1024) {
+	fread(header, 1, MIN(ARRAY_SIZE(header), kernel_size), f) !=
+	MIN(ARRAY_SIZE(header), kernel_size)) {
 	fprintf(stderr, "qemu: could not load kernel '%s'\n",
 		kernel_filename);
 	exit(1);
@@ -630,8 +824,14 @@ static void load_linux(target_phys_addr_t option_rom,
 #endif
     if (ldl_p(header+0x202) == 0x53726448)
 	protocol = lduw_p(header+0x206);
-    else
+    else {
+	/* This looks like a multiboot kernel. If it is, let's stop
+	   treating it like a Linux kernel. */
+	if (load_multiboot(fw_cfg, f, kernel_filename,
+                           initrd_filename, kernel_cmdline, header))
+	   return;
 	protocol = 0;
+    }
 
     if (protocol < 0x200 || !(header[0x211] & 0x01)) {
 	/* Low kernel */
@@ -721,16 +921,25 @@ static void load_linux(target_phys_addr_t option_rom,
     }
 
     /* store the finalized header and load the rest of the kernel */
-    cpu_physical_memory_write(real_addr, header, 1024);
+    cpu_physical_memory_write(real_addr, header, ARRAY_SIZE(header));
 
     setup_size = header[0x1f1];
     if (setup_size == 0)
 	setup_size = 4;
 
     setup_size = (setup_size+1)*512;
-    kernel_size -= setup_size;	/* Size of protected-mode code */
+    /* Size of protected-mode code */
+    kernel_size -= (setup_size > ARRAY_SIZE(header)) ? setup_size : ARRAY_SIZE(header);
+
+    /* In case we have read too much already, copy that over */
+    if (setup_size < ARRAY_SIZE(header)) {
+        cpu_physical_memory_write(prot_addr, header + setup_size, ARRAY_SIZE(header) - setup_size);
+        prot_addr += (ARRAY_SIZE(header) - setup_size);
+        setup_size = ARRAY_SIZE(header);
+    }
 
-    if (!fread_targphys_ok(real_addr+1024, setup_size-1024, f) ||
+    if (!fread_targphys_ok(real_addr + ARRAY_SIZE(header),
+                           setup_size - ARRAY_SIZE(header), f) ||
 	!fread_targphys_ok(prot_addr, kernel_size, f)) {
 	fprintf(stderr, "qemu: read error on kernel '%s'\n",
 		kernel_filename);
@@ -981,7 +1190,7 @@ static void pc_init1(ram_addr_t ram_size,
     fw_cfg = bochs_bios_init();
 
     if (linux_boot) {
-        load_linux(0xc0000 + oprom_area_size,
+        load_linux(fw_cfg, 0xc0000 + oprom_area_size,
                    kernel_filename, initrd_filename, kernel_cmdline, below_4g_mem_size);
         oprom_area_size += 2048;
     }
diff --git a/pc-bios/multiboot/multiboot.S b/pc-bios/multiboot/multiboot.S
new file mode 100644
index 0000000..d0eec26
--- /dev/null
+++ b/pc-bios/multiboot/multiboot.S
@@ -0,0 +1,209 @@
+/*
+ * Multiboot Option ROM
+ *
+ * This program is free software; you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation; either version 2 of the License, or
+ * (at your option) any later version.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with this program; if not, write to the Free Software
+ * Foundation, 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301, USA.
+ *
+ * Copyright Novell Inc, 2009
+ *   Authors: Alexander Graf <agraf@suse.de>
+ */
+
+#define NO_QEMU_PROTOS
+#include "../../hw/fw_cfg.h"
+
+#define BIOS_CFG_IOPORT_CFG	0x510
+#define BIOS_CFG_IOPORT_DATA	0x511
+
+#define MULTIBOOT_MAGIC		0x2badb002
+
+/* Read a variable from the fw_cfg device.
+   Clobbers:	%edx
+   Out:		%eax */
+.macro read_fw VAR
+	mov		$\VAR, %ax
+	mov		$BIOS_CFG_IOPORT_CFG, %dx
+	outw		%ax, (%dx)
+	mov		$BIOS_CFG_IOPORT_DATA, %dx
+	inb		(%dx), %al
+	shl		$8, %eax
+	inb		(%dx), %al
+	shl		$8, %eax
+	inb		(%dx), %al
+	shl		$8, %eax
+	inb		(%dx), %al
+	bswap		%eax
+.endm
+
+.code16
+.text
+	.global 	_start
+_start:
+	.short		0xaa55
+	.byte		(_end - _start) / 512
+	push		%eax
+	push		%ds
+
+	/* setup ds so we can access the IVT */
+	xor		%ax, %ax
+	mov		%ax, %ds
+
+	/* save old int 19 */
+	mov		(0x19*4), %eax
+	mov		%eax, %cs:old_int19
+
+	/* install our int 19 handler */
+	movw		$int19_handler, (0x19*4)
+	mov		%cs, (0x19*4+2)
+
+	pop		%ds
+	pop		%eax
+	lret
+
+int19_handler:
+	/* DS = CS */
+	movw		%cs, %ax
+	movw		%ax, %ds
+
+	/* fall through */
+
+run_multiboot:
+
+	cli
+	cld
+
+	mov		%cs, %eax
+	shl		$0x4, %eax
+
+	/* fix the gdt descriptor to be PC relative */
+	mov		(gdt_desc+2), %ebx
+	add		%eax, %ebx
+	mov		%ebx, (gdt_desc+2)
+
+	/* fix the prot mode indirect jump to be PC relative */
+	mov		(prot_jump), %ebx
+	add		%eax, %ebx
+	mov		%ebx, (prot_jump)
+
+	/* FS = bootinfo_struct */
+	read_fw		FW_CFG_INITRD_ADDR
+	shr		$4, %eax
+	mov		%ax, %fs
+
+	/* ES = mmap_addr */
+	read_fw		FW_CFG_INITRD_SIZE
+	shr		$4, %eax
+	mov		%ax, %es
+
+	/* Initialize multiboot mmap structs using int 0x15(e820) */
+	xor		%ebx, %ebx
+	/* mmap start after first size */
+	movl		$4, %edi
+
+mmap_loop:
+	/* entry size (mmap struct) & max buffer size (int15) */
+	movl		$20, %ecx
+	/* store entry size */
+	movl		%ecx, %es:-4(%edi)
+	/* e820 */
+	movl		$0x0000e820, %eax
+	/* 'SMAP' magic */
+	movl		$0x534d4150, %edx
+	int		$0x15
+
+mmap_check_entry:
+	/* last entry? then we're done */
+	jb		mmap_done
+	and		%bx, %bx
+	jz		mmap_done
+	/* valid entry, so let's loop on */
+
+mmap_store_entry:
+	/* %ax = entry_number * 24 */
+	mov		$24, %ax
+	mul		%bx
+	mov		%ax, %di
+	movw		%di, %fs:0x2c
+	/* %di = 4 + (entry_number * 24) */
+	add		$4, %di
+	jmp		mmap_loop
+
+mmap_done:
+real_to_prot:
+	/* Load the GDT before going into protected mode */
+lgdt:
+	data32 lgdt	%cs:gdt_desc
+
+	/* get us to protected mode now */
+	movl		$1, %eax
+	movl		%eax, %cr0
+
+	/* the LJMP sets CS for us and gets us to 32-bit */
+ljmp:
+	data32 ljmp	*%cs:prot_jump
+
+prot_mode:
+.code32
+
+	/* initialize all other segments */
+	movl		$0x10, %eax
+	movl		%eax, %ss
+	movl		%eax, %ds
+	movl		%eax, %es
+	movl		%eax, %fs
+	movl		%eax, %gs
+
+	/* Jump off to the kernel */
+	read_fw		FW_CFG_KERNEL_ADDR
+	mov		%eax, %ecx
+
+	/* EBX contains a pointer to the bootinfo struct */
+	read_fw		FW_CFG_INITRD_ADDR
+	movl		%eax, %ebx
+
+	/* EAX has to contain the magic */
+	movl		$MULTIBOOT_MAGIC, %eax
+ljmp2:
+	jmp		*%ecx
+
+/* Variables */
+.align 4, 0
+old_int19:	.long 0
+
+prot_jump:	.long prot_mode
+		.short 8
+
+.align 4, 0
+gdt:
+	/* 0x00 */
+.byte	0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00
+
+	/* 0x08: code segment (base=0, limit=0xfffff, type=32bit code exec/read, DPL=0, 4k) */
+.byte	0xff, 0xff, 0x00, 0x00, 0x00, 0x9a, 0xcf, 0x00
+
+	/* 0x10: data segment (base=0, limit=0xfffff, type=32bit data read/write, DPL=0, 4k) */
+.byte	0xff, 0xff, 0x00, 0x00, 0x00, 0x92, 0xcf, 0x00
+
+	/* 0x18: code segment (base=0, limit=0x0ffff, type=16bit code exec/read/conf, DPL=0, 1b) */
+.byte	0xff, 0xff, 0x00, 0x00, 0x00, 0x9e, 0x00, 0x00
+
+	/* 0x20: data segment (base=0, limit=0x0ffff, type=16bit data read/write, DPL=0, 1b) */
+.byte	0xff, 0xff, 0x00, 0x00, 0x00, 0x92, 0x00, 0x00
+
+gdt_desc:
+.short	(5 * 8) - 1
+.long	gdt
+
+.align 512, 0
+_end:
+
-- 
1.6.0.2