Commit cdebec5e authored by Paolo Bonzini's avatar Paolo Bonzini
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linuxboot: compute initrd loading address 



Even though hw/i386/pc.c tries to compute a valid loading address for the
initrd, close to the top of RAM, this does not take into account other
data that is malloced into that memory by SeaBIOS.

Luckily we can easily look at the memory map to find out how much memory is
used up there.  This patch places the initrd in the first four gigabytes,
below the first hole (as returned by INT 15h, AX=e801h).

Without this patch:
[    0.000000] init_memory_mapping: [mem 0x07000000-0x07fdffff]
[    0.000000] RAMDISK: [mem 0x0710a000-0x07fd7fff]

With this patch:
[    0.000000] init_memory_mapping: [mem 0x07000000-0x07fdffff]
[    0.000000] RAMDISK: [mem 0x07112000-0x07fdffff]

So linuxboot is able to use the 64k that were added as padding for
QEMU <= 2.1.

Acked-by: default avatarMichael S. Tsirkin <mst@redhat.com>
Signed-off-by: default avatarPaolo Bonzini <pbonzini@redhat.com>
parent fc02086b

pc-bios/linuxboot.bin

(1 KiB)

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pc-bios/optionrom/linuxboot.S

+43 −4
Original line number Diff line number Diff line
@@ -76,6 +76,37 @@ boot_kernel: 




copy_kernel:

	/* Compute initrd address */

	mov		$0xe801, %ax

	xor		%cx, %cx

	xor		%dx, %dx

	int		$0x15



	/* Output could be in AX/BX or CX/DX */

	or		%cx, %cx

	jnz		1f

	or		%dx, %dx

	jnz		1f

	mov		%ax, %cx

	mov		%bx, %dx

1:



	or		%dx, %dx

	jnz		2f

	addw		$1024, %cx            /* add 1 MB */

	movzwl		%cx, %edi

	shll		$10, %edi             /* convert to bytes */

	jmp		3f



2:

	addw		$16777216 >> 16, %dx  /* add 16 MB */

	movzwl		%dx, %edi

	shll		$16, %edi             /* convert to bytes */



3:

	read_fw         FW_CFG_INITRD_SIZE

	subl            %eax, %edi

	andl            $-4096, %edi          /* EDI = start of initrd */



	/* 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
@@ -108,10 +139,18 @@ copy_kernel: 
	/* We're now running in 16-bit CS, but 32-bit ES! */



	/* Load kernel and initrd */

	pushl		%edi

	read_fw_blob_addr32_edi(FW_CFG_INITRD)

	read_fw_blob_addr32(FW_CFG_KERNEL)

	read_fw_blob_addr32(FW_CFG_INITRD)

	read_fw_blob_addr32(FW_CFG_CMDLINE)

	read_fw_blob_addr32(FW_CFG_SETUP)



	read_fw		FW_CFG_SETUP_ADDR

	mov		%eax, %edi

	mov		%eax, %ebx

	read_fw_blob_addr32_edi(FW_CFG_SETUP)



	/* Update the header with the initrd address we chose above */

	popl		%es:0x218(%ebx)



	/* And now jump into Linux! */

	mov		$0, %eax

pc-bios/optionrom/optionrom.h

+18 −3
Original line number Diff line number Diff line
@@ -51,8 +51,6 @@ 
.endm



#define read_fw_blob_pre(var)				\

	read_fw		var ## _ADDR;			\

	mov		%eax, %edi;			\

	read_fw		var ## _SIZE;			\

	mov		%eax, %ecx;			\

	mov		$var ## _DATA, %ax;		\
@@ -68,6 +66,8 @@ 
 * Clobbers:	%eax, %edx, %es, %ecx, %edi

 */

#define read_fw_blob(var)				\

	read_fw		var ## _ADDR;			\

	mov		%eax, %edi;			\

	read_fw_blob_pre(var);				\

	/* old as(1) doesn't like this insn so emit the bytes instead: \

	rep insb	(%dx), %es:(%edi);		\
@@ -81,6 +81,21 @@ 
 * Clobbers:	%eax, %edx, %es, %ecx, %edi

 */

#define read_fw_blob_addr32(var)			\

	read_fw		var ## _ADDR;			\

	mov		%eax, %edi;			\

	read_fw_blob_pre(var);				\

	/* old as(1) doesn't like this insn so emit the bytes instead: \

	addr32 rep insb	(%dx), %es:(%edi);		\

	*/						\

	.dc.b		0x67,0xf3,0x6c



/*

 * Read a blob from the fw_cfg device in forced addr32 mode, address is in %edi.

 * Requires _SIZE and _DATA values for the parameter.

 *

 * Clobbers:	%eax, %edx, %edi, %es, %ecx

 */

#define read_fw_blob_addr32_edi(var)			\

	read_fw_blob_pre(var);				\

	/* old as(1) doesn't like this insn so emit the bytes instead: \

	addr32 rep insb	(%dx), %es:(%edi);		\