i386: move kernel

Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Signed-off-by: Ingo Molnar <mingo@elte.hu>

1 files changed, 122 insertions, 0 deletions

diff --git a/arch/x86/kernel/efi_stub_32.S b/arch/x86/kernel/efi_stub_32.S
new file mode 100644
index 00000000000..ef00bb77d7e
--- /dev/null
+++ b/arch/x86/kernel/efi_stub_32.S
@@ -0,0 +1,122 @@
+/*
+ * EFI call stub for IA32.
+ *
+ * This stub allows us to make EFI calls in physical mode with interrupts
+ * turned off.
+ */
+
+#include <linux/linkage.h>
+#include <asm/page.h>
+
+/*
+ * efi_call_phys(void *, ...) is a function with variable parameters.
+ * All the callers of this function assure that all the parameters are 4-bytes.
+ */
+
+/*
+ * In gcc calling convention, EBX, ESP, EBP, ESI and EDI are all callee save.
+ * So we'd better save all of them at the beginning of this function and restore
+ * at the end no matter how many we use, because we can not assure EFI runtime
+ * service functions will comply with gcc calling convention, too.
+ */
+
+.text
+ENTRY(efi_call_phys)
+	/*
+	 * 0. The function can only be called in Linux kernel. So CS has been
+	 * set to 0x0010, DS and SS have been set to 0x0018. In EFI, I found
+	 * the values of these registers are the same. And, the corresponding
+	 * GDT entries are identical. So I will do nothing about segment reg
+	 * and GDT, but change GDT base register in prelog and epilog.
+	 */
+
+	/*
+	 * 1. Now I am running with EIP = <physical address> + PAGE_OFFSET.
+	 * But to make it smoothly switch from virtual mode to flat mode.
+	 * The mapping of lower virtual memory has been created in prelog and
+	 * epilog.
+	 */
+	movl	$1f, %edx
+	subl	$__PAGE_OFFSET, %edx
+	jmp	*%edx
+1:
+
+	/*
+	 * 2. Now on the top of stack is the return
+	 * address in the caller of efi_call_phys(), then parameter 1,
+	 * parameter 2, ..., param n. To make things easy, we save the return
+	 * address of efi_call_phys in a global variable.
+	 */
+	popl	%edx
+	movl	%edx, saved_return_addr
+	/* get the function pointer into ECX*/
+	popl	%ecx
+	movl	%ecx, efi_rt_function_ptr
+	movl	$2f, %edx
+	subl	$__PAGE_OFFSET, %edx
+	pushl	%edx
+
+	/*
+	 * 3. Clear PG bit in %CR0.
+	 */
+	movl	%cr0, %edx
+	andl	$0x7fffffff, %edx
+	movl	%edx, %cr0
+	jmp	1f
+1:
+
+	/*
+	 * 4. Adjust stack pointer.
+	 */
+	subl	$__PAGE_OFFSET, %esp
+
+	/*
+	 * 5. Call the physical function.
+	 */
+	jmp	*%ecx
+
+2:
+	/*
+	 * 6. After EFI runtime service returns, control will return to
+	 * following instruction. We'd better readjust stack pointer first.
+	 */
+	addl	$__PAGE_OFFSET, %esp
+
+	/*
+	 * 7. Restore PG bit
+	 */
+	movl	%cr0, %edx
+	orl	$0x80000000, %edx
+	movl	%edx, %cr0
+	jmp	1f
+1:
+	/*
+	 * 8. Now restore the virtual mode from flat mode by
+	 * adding EIP with PAGE_OFFSET.
+	 */
+	movl	$1f, %edx
+	jmp	*%edx
+1:
+
+	/*
+	 * 9. Balance the stack. And because EAX contain the return value,
+	 * we'd better not clobber it.
+	 */
+	leal	efi_rt_function_ptr, %edx
+	movl	(%edx), %ecx
+	pushl	%ecx
+
+	/*
+	 * 10. Push the saved return address onto the stack and return.
+	 */
+	leal	saved_return_addr, %edx
+	movl	(%edx), %ecx
+	pushl	%ecx
+	ret
+.previous
+
+.data
+saved_return_addr:
+	.long 0
+efi_rt_function_ptr:
+	.long 0