Patchwork [5/6] Convert linux bootrom to external rom and fw_cfg

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Submitter Alexander Graf
Date Nov. 12, 2009, 8:53 p.m.
Message ID <1258059195-17582-6-git-send-email-agraf@suse.de>
Download mbox | patch
Permalink /patch/38290/
State New
Headers show

Comments

Alexander Graf - Nov. 12, 2009, 8:53 p.m.
We already have a working multiboot implementation that uses fw_cfg to get
its kernel module etc. data in int19 runtime now.

So what's missing is a working linux boot option rom. While at it I figured it
would be a good idea to take the opcode generator out of pc.c and instead use
a proper option rom, like we do with multiboot.

So here it is - an fw_cfg using option rom for -kernel with linux!

Signed-off-by: Alexander Graf <agraf@suse.de>
---
 hw/fw_cfg.h                   |    8 ++-
 hw/pc.c                       |  126 +++++++------------------------------
 pc-bios/optionrom/Makefile    |    2 +-
 pc-bios/optionrom/linuxboot.S |  140 +++++++++++++++++++++++++++++++++++++++++
 4 files changed, 172 insertions(+), 104 deletions(-)
 create mode 100644 pc-bios/optionrom/linuxboot.S
Paolo Bonzini - Nov. 13, 2009, 6:37 a.m.
On 11/12/2009 09:53 PM, Alexander Graf wrote:
> +	/* Set DS to SS+SP - 0x10, so we can write our GDT descriptor there */
> +	mov		%ss, %eax
> +	shl		$4, %eax
> +	add		%esp, %eax
> +	sub		$0x10, %eax
> +	shr		$4, %eax

Dead code?  Or wrong comment and missing mov %eax, %gs?

Also, I know this is running with disabled interrupts, but why set %gs 
just below the stack instead of decrementing %esp?

> +	/* Now create the GDT descriptor */
> +	mov		%cs, %eax

Paolo
Alexander Graf - Nov. 25, 2009, 10:38 a.m.
On 13.11.2009, at 07:37, Paolo Bonzini wrote:

> On 11/12/2009 09:53 PM, Alexander Graf wrote:
>> +	/* Set DS to SS+SP - 0x10, so we can write our GDT descriptor there */
>> +	mov		%ss, %eax
>> +	shl		$4, %eax
>> +	add		%esp, %eax
>> +	sub		$0x10, %eax
>> +	shr		$4, %eax
> 
> Dead code?  Or wrong comment and missing mov %eax, %gs?

The latter.

> Also, I know this is running with disabled interrupts, but why set %gs just below the stack instead of decrementing %esp?

Uh. Decrementing %esp should work too I guess. That's just what I came up with.

Alex

Patch

diff --git a/hw/fw_cfg.h b/hw/fw_cfg.h
index 1e004b7..7070c94 100644
--- a/hw/fw_cfg.h
+++ b/hw/fw_cfg.h
@@ -20,7 +20,13 @@ 
 #define FW_CFG_KERNEL_ENTRY     0x10
 #define FW_CFG_KERNEL_DATA      0x11
 #define FW_CFG_INITRD_DATA      0x12
-#define FW_CFG_MAX_ENTRY        0x13
+#define FW_CFG_CMDLINE_ADDR     0x13
+#define FW_CFG_CMDLINE_SIZE     0x14
+#define FW_CFG_CMDLINE_DATA     0x15
+#define FW_CFG_SETUP_ADDR       0x16
+#define FW_CFG_SETUP_SIZE       0x17
+#define FW_CFG_SETUP_DATA       0x18
+#define FW_CFG_MAX_ENTRY        0x19
 
 #define FW_CFG_WRITE_CHANNEL    0x4000
 #define FW_CFG_ARCH_LOCAL       0x8000
diff --git a/hw/pc.c b/hw/pc.c
index 55bd1a4..7c791c4 100644
--- a/hw/pc.c
+++ b/hw/pc.c
@@ -487,85 +487,6 @@  static void *bochs_bios_init(void)
     return fw_cfg;
 }
 
-/* Generate an initial boot sector which sets state and jump to
-   a specified vector */
-static void generate_bootsect(uint32_t gpr[8], uint16_t segs[6], uint16_t ip)
-{
-    uint8_t rom[512], *p, *reloc;
-    uint8_t sum;
-    int i;
-
-    memset(rom, 0, sizeof(rom));
-
-    p = rom;
-    /* Make sure we have an option rom signature */
-    *p++ = 0x55;
-    *p++ = 0xaa;
-
-    /* ROM size in sectors*/
-    *p++ = 1;
-
-    /* Hook int19 */
-
-    *p++ = 0x50;		/* push ax */
-    *p++ = 0x1e;		/* push ds */
-    *p++ = 0x31; *p++ = 0xc0;	/* xor ax, ax */
-    *p++ = 0x8e; *p++ = 0xd8;	/* mov ax, ds */
-
-    *p++ = 0xc7; *p++ = 0x06;   /* movvw _start,0x64 */
-    *p++ = 0x64; *p++ = 0x00;
-    reloc = p;
-    *p++ = 0x00; *p++ = 0x00;
-
-    *p++ = 0x8c; *p++ = 0x0e;   /* mov cs,0x66 */
-    *p++ = 0x66; *p++ = 0x00;
-
-    *p++ = 0x1f;		/* pop ds */
-    *p++ = 0x58;		/* pop ax */
-    *p++ = 0xcb;		/* lret */
-
-    /* Actual code */
-    *reloc = (p - rom);
-
-    *p++ = 0xfa;		/* CLI */
-    *p++ = 0xfc;		/* CLD */
-
-    for (i = 0; i < 6; i++) {
-	if (i == 1)		/* Skip CS */
-	    continue;
-
-	*p++ = 0xb8;		/* MOV AX,imm16 */
-	*p++ = segs[i];
-	*p++ = segs[i] >> 8;
-	*p++ = 0x8e;		/* MOV <seg>,AX */
-	*p++ = 0xc0 + (i << 3);
-    }
-
-    for (i = 0; i < 8; i++) {
-	*p++ = 0x66;		/* 32-bit operand size */
-	*p++ = 0xb8 + i;	/* MOV <reg>,imm32 */
-	*p++ = gpr[i];
-	*p++ = gpr[i] >> 8;
-	*p++ = gpr[i] >> 16;
-	*p++ = gpr[i] >> 24;
-    }
-
-    *p++ = 0xea;		/* JMP FAR */
-    *p++ = ip;			/* IP */
-    *p++ = ip >> 8;
-    *p++ = segs[1];		/* CS */
-    *p++ = segs[1] >> 8;
-
-    /* sign rom */
-    sum = 0;
-    for (i = 0; i < (sizeof(rom) - 1); i++)
-        sum += rom[i];
-    rom[sizeof(rom) - 1] = -sum;
-
-    rom_add_blob("linux-bootsect", rom, sizeof(rom),
-                 PC_ROM_MIN_OPTION, PC_ROM_MAX, PC_ROM_ALIGN);
-}
-
 static long get_file_size(FILE *f)
 {
     long where, size;
@@ -812,12 +733,9 @@  static void load_linux(void *fw_cfg,
                        target_phys_addr_t max_ram_size)
 {
     uint16_t protocol;
-    uint32_t gpr[8];
-    uint16_t seg[6];
-    uint16_t real_seg;
     int setup_size, kernel_size, initrd_size = 0, cmdline_size;
     uint32_t initrd_max;
-    uint8_t header[8192], *setup, *kernel;
+    uint8_t header[8192], *setup, *kernel, *initrd_data;
     target_phys_addr_t real_addr, prot_addr, cmdline_addr, initrd_addr = 0;
     FILE *f;
     char *vmode;
@@ -886,9 +804,11 @@  static void load_linux(void *fw_cfg,
     if (initrd_max >= max_ram_size-ACPI_DATA_SIZE)
     	initrd_max = max_ram_size-ACPI_DATA_SIZE-1;
 
-    /* kernel command line */
-    rom_add_blob_fixed("cmdline", kernel_cmdline,
-                       strlen(kernel_cmdline)+1, cmdline_addr);
+    fw_cfg_add_i32(fw_cfg, FW_CFG_CMDLINE_ADDR, cmdline_addr);
+    fw_cfg_add_i32(fw_cfg, FW_CFG_CMDLINE_SIZE, strlen(kernel_cmdline)+1);
+    fw_cfg_add_bytes(fw_cfg, FW_CFG_CMDLINE_DATA,
+                     (uint8_t*)strdup(kernel_cmdline),
+                     strlen(kernel_cmdline)+1);
 
     if (protocol >= 0x202) {
 	stl_p(header+0x228, cmdline_addr);
@@ -937,7 +857,13 @@  static void load_linux(void *fw_cfg,
 
 	initrd_size = get_image_size(initrd_filename);
         initrd_addr = (initrd_max-initrd_size) & ~4095;
-        rom_add_file_fixed(initrd_filename, initrd_addr);
+
+        initrd_data = qemu_malloc(initrd_size);
+        load_image(initrd_filename, initrd_data);
+
+        fw_cfg_add_i32(fw_cfg, FW_CFG_INITRD_ADDR, initrd_addr);
+        fw_cfg_add_i32(fw_cfg, FW_CFG_INITRD_SIZE, initrd_size);
+        fw_cfg_add_bytes(fw_cfg, FW_CFG_INITRD_DATA, initrd_data, initrd_size);
 
 	stl_p(header+0x218, initrd_addr);
 	stl_p(header+0x21c, initrd_size);
@@ -957,21 +883,17 @@  static void load_linux(void *fw_cfg,
     fread(kernel, 1, kernel_size, f);
     fclose(f);
     memcpy(setup, header, MIN(sizeof(header), setup_size));
-    rom_add_blob_fixed("linux-setup", setup,
-                       setup_size, real_addr);
-    rom_add_blob_fixed(kernel_filename, kernel,
-                       kernel_size, prot_addr);
-    qemu_free(setup);
-    qemu_free(kernel);
-
-    /* generate bootsector to set up the initial register state */
-    real_seg = real_addr >> 4;
-    seg[0] = seg[2] = seg[3] = seg[4] = seg[4] = real_seg;
-    seg[1] = real_seg+0x20;	/* CS */
-    memset(gpr, 0, sizeof gpr);
-    gpr[4] = cmdline_addr-real_addr-16;	/* SP (-16 is paranoia) */
-
-    generate_bootsect(gpr, seg, 0);
+
+    fw_cfg_add_i32(fw_cfg, FW_CFG_KERNEL_ADDR, prot_addr);
+    fw_cfg_add_i32(fw_cfg, FW_CFG_KERNEL_SIZE, kernel_size);
+    fw_cfg_add_bytes(fw_cfg, FW_CFG_KERNEL_DATA, kernel, kernel_size);
+
+    fw_cfg_add_i32(fw_cfg, FW_CFG_SETUP_ADDR, real_addr);
+    fw_cfg_add_i32(fw_cfg, FW_CFG_SETUP_SIZE, setup_size);
+    fw_cfg_add_bytes(fw_cfg, FW_CFG_SETUP_DATA, setup, setup_size);
+
+    option_rom[nb_option_roms] = "linuxboot.bin";
+    nb_option_roms++;
 }
 
 static const int ide_iobase[2] = { 0x1f0, 0x170 };
diff --git a/pc-bios/optionrom/Makefile b/pc-bios/optionrom/Makefile
index b01a54e..54db882 100644
--- a/pc-bios/optionrom/Makefile
+++ b/pc-bios/optionrom/Makefile
@@ -13,7 +13,7 @@  CFLAGS += -I$(SRC_PATH)
 CFLAGS += $(call cc-option, $(CFLAGS), -fno-stack-protector)
 QEMU_CFLAGS = $(CFLAGS)
 
-build-all: multiboot.bin
+build-all: multiboot.bin linuxboot.bin
 
 %.img: %.o
 	$(call quiet-command,$(LD) -Ttext 0 -e _start -s -o $@ $<,"  Building $(TARGET_DIR)$@")
diff --git a/pc-bios/optionrom/linuxboot.S b/pc-bios/optionrom/linuxboot.S
new file mode 100644
index 0000000..842dd3d
--- /dev/null
+++ b/pc-bios/optionrom/linuxboot.S
@@ -0,0 +1,140 @@ 
+/*
+ * Linux Boot 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, see <http://www.gnu.org/licenses/>.
+ *
+ * Copyright Novell Inc, 2009
+ *   Authors: Alexander Graf <agraf@suse.de>
+ *
+ * Based on code in hw/pc.c.
+ */
+
+#include "optionrom.h"
+
+BOOT_ROM_START
+
+run_linuxboot:
+
+	cli
+	cld
+
+	jmp		copy_kernel
+boot_kernel:
+
+	read_fw		FW_CFG_SETUP_ADDR
+
+	mov		%eax, %ebx
+	shr		$4, %ebx
+
+	/* All segments contain real_addr */
+	mov		%bx, %ds
+	mov		%bx, %es
+	mov		%bx, %fs
+	mov		%bx, %gs
+	mov		%bx, %ss
+
+	/* CX = CS we want to jump to */
+	add		$0x20, %bx
+	mov		%bx, %cx
+
+	/* SP = cmdline_addr-real_addr-16 */
+	read_fw		FW_CFG_CMDLINE_ADDR
+	mov		%eax, %ebx
+	read_fw		FW_CFG_SETUP_ADDR
+	sub		%eax, %ebx
+	sub		$16, %ebx
+	mov		%ebx, %esp
+
+	/* Build indirect retf descriptor */
+	pushw		%cx		/* CS */
+	xor		%ax, %ax
+	pushw		%ax		/* IP = 0 */
+
+	/* Clear registers */
+	xor		%eax, %eax
+	xor		%ebx, %ebx
+	xor		%ecx, %ecx
+	xor		%edx, %edx
+	xor		%edi, %edi
+	xor		%ebp, %ebp
+
+	/* Jump to Linux */
+	retf
+
+
+copy_kernel:
+
+	/* We need to load the kernel into memory we can't access in 16 bit
+	   mode, so let's get into 32 bit mode, write the kernel and jump
+	   back again. */
+
+	/* Set DS to SS+SP - 0x10, so we can write our GDT descriptor there */
+	mov		%ss, %eax
+	shl		$4, %eax
+	add		%esp, %eax
+	sub		$0x10, %eax
+	shr		$4, %eax
+
+	/* Now create the GDT descriptor */
+	mov		%cs, %eax
+	shl		$4, %eax
+	movw		$((3 * 8) - 1), %bx
+	movw		%bx, %gs:0
+	movl		$gdt, %ebx
+	add		%eax, %ebx
+	movl		%ebx, %gs:2
+
+	/* And load the GDT */
+	data32 lgdt	%gs:0
+
+	/* Get us to protected mode now */
+	mov		$1, %eax
+	mov		%eax, %cr0
+
+	/* So we can set DS to a 32-bit segment */
+	mov		$0x10, %eax
+	mov		%eax, %ds
+
+	/* We're now running in 16-bit CS, but 32-bit DS! */
+
+	/* Load kernel and initrd */
+	read_fw_blob(FW_CFG_KERNEL)
+	read_fw_blob(FW_CFG_INITRD)
+	read_fw_blob(FW_CFG_CMDLINE)
+	read_fw_blob(FW_CFG_SETUP)
+
+	/* And now jump into Linux! */
+	mov		$0, %eax
+	mov		%eax, %cr0
+
+	/* DS = CS */
+	mov		%cs, %ax
+	mov		%ax, %ds
+
+	jmp		boot_kernel
+
+/* Variables */
+
+.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
+
+BOOT_ROM_END