Add qemu 2.4.0

[kvmfornfv.git] / qemu / roms / openbios / arch / amd64 / switch.S

diff --git a/qemu/roms/openbios/arch/amd64/switch.S b/qemu/roms/openbios/arch/amd64/switch.S
new file mode 100644 (file)
index 0000000..6666815
--- /dev/null
+++ b/qemu/roms/openbios/arch/amd64/switch.S
@@ -0,0 +1,116 @@
+       .globl  entry, __switch_context, __exit_context, halt
+
+       .text
+       .align  4
+
+/*
+ * Entry point
+ * We start execution from here.
+ * It is assumed that CPU is in 32-bit protected mode and
+ * all segments are 4GB and base zero (flat model).
+ */
+entry:
+       /* Save boot context and switch to our main context.
+        * Main context is statically defined in C.
+        */
+       pushl   %cs
+       call    __switch_context
+
+       /* We get here when the main context switches back to
+        * the boot context.
+        * Return to previous bootloader.
+        */
+       ret
+
+/*
+ * Switch execution context
+ * This saves registers, segments, and GDT in the stack, then
+ * switches the stack, and restores everything from the new stack.
+ * This function takes no argument. New stack pointer is
+ * taken from global variable __context, and old stack pointer
+ * is also saved to __context. This way we can just jump to
+ * this routine to get back to the original context.
+ *
+ * Call this routine with lcall or pushl %cs; call.
+ */
+__switch_context:
+       /* Save everything in current stack */
+       pushfl              /* 56 */
+       pushl   %ds         /* 52 */
+       pushl   %es         /* 48 */
+       pushl   %fs         /* 44 */
+       pushl   %gs         /* 40 */
+       pushal              /* 8 */
+       subl    $8, %esp
+       movw    %ss, (%esp) /* 0 */
+       sgdt    2(%esp)     /* 2 */
+
+#if 0
+       /* Swap %cs and %eip on the stack, so lret will work */
+       movl    60(%esp), %eax
+       xchgl   %eax, 64(%esp)
+       movl    %eax, 60(%esp)
+#endif
+
+       /* At this point we don't know if we are on flat segment
+        * or relocated. So compute the address offset from %eip.
+        * Assuming CS.base==DS.base==SS.base.
+        */
+       call    1f
+1:     popl    %ebx
+       subl    $1b, %ebx
+
+       /* Interrupts are not allowed... */
+       cli
+
+       /* Current context pointer is our stack pointer */
+       movl    %esp, %esi
+
+       /* Normalize the ctx pointer */
+       subl    %ebx, %esi
+
+       /* Swap it with new value */
+       xchgl   %esi, __context(%ebx)
+
+       /* Adjust new ctx pointer for current address offset */
+       addl    %ebx, %esi
+
+       /* Load new %ss and %esp to temporary */
+       movzwl  (%esi), %edx
+       movl    20(%esi), %eax
+
+       /* Load new GDT */
+       lgdt    2(%esi)
+
+       /* Load new stack segment with new GDT */
+       movl    %edx, %ss
+
+       /* Set new stack pointer, but we have to adjust it because
+        * pushal saves %esp value before pushal, and we want the value
+        * after pushal.
+        */
+       leal    -32(%eax), %esp
+
+       /* Load the rest from new stack */
+       popal
+       popl    %gs
+       popl    %fs
+       popl    %es
+       popl    %ds
+       popfl
+
+       /* Finally, load new %cs and %eip */
+       lret
+
+__exit_context:
+       /* Get back to the original context */
+       pushl   %cs
+       call    __switch_context
+
+       /* We get here if the other context attempt to switch to this
+        * dead context. This should not happen. */
+
+halt:
+       cli
+       hlt
+       jmp     halt