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: Michael S. Tsirkin <mst@redhat.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>

diff --git a/pc-bios/linuxboot.bin b/pc-bios/linuxboot.bin
index e7c36694f997c3c34f7f4af3c2923bd2ef6094e7..130103fb739228a6869aaf1b174b9d20c13378fc 100644 (file)
Binary files a/pc-bios/linuxboot.bin and b/pc-bios/linuxboot.bin differ

diff --git a/pc-bios/optionrom/linuxboot.S b/pc-bios/optionrom/linuxboot.S
index 748c831160983dd711284f7af33803b6d0f07e07..5bc0af08e0f7dc7abdf55320baf0461170342f0f 100644 (file)
--- a/pc-bios/optionrom/linuxboot.S
+++ b/pc-bios/optionrom/linuxboot.S
@@ -76,14 +76,45 @@ 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
           back again. */
 
        /* Reserve space on the stack for our GDT descriptor. */
-       mov             %esp, %ebp
-       sub             $16, %esp
+       mov             %esp, %ebp
+       sub             $16, %esp
 
        /* Now create the GDT descriptor */
        movw            $((3 * 8) - 1), -16(%bp)
@@ -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

diff --git a/pc-bios/optionrom/optionrom.h b/pc-bios/optionrom/optionrom.h
index ce436085d9ba9e3a97229d0bf59b38b57942848d..f1a9021ec13b8bb1bd2bb51d4bee21429d6e24be 100644 (file)
--- a/pc-bios/optionrom/optionrom.h
+++ b/pc-bios/optionrom/optionrom.h
@@ -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);              \
@@ -80,7 +80,22 @@
  *
  * Clobbers:   %eax, %edx, %es, %ecx, %edi
  */
-#define read_fw_blob_addr32(var)                               \
+#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);              \