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authorLinus Torvalds <torvalds@ppc970.osdl.org>2005-04-16 15:20:36 -0700
committerLinus Torvalds <torvalds@ppc970.osdl.org>2005-04-16 15:20:36 -0700
commit1da177e4c3f41524e886b7f1b8a0c1fc7321cac2 (patch)
tree0bba044c4ce775e45a88a51686b5d9f90697ea9d /arch/i386/kernel/efi_stub.S
downloadconfigs-1da177e4c3f41524e886b7f1b8a0c1fc7321cac2.tar.gz
Linux-2.6.12-rc2v2.6.12-rc2
Initial git repository build. I'm not bothering with the full history, even though we have it. We can create a separate "historical" git archive of that later if we want to, and in the meantime it's about 3.2GB when imported into git - space that would just make the early git days unnecessarily complicated, when we don't have a lot of good infrastructure for it. Let it rip!
Diffstat (limited to 'arch/i386/kernel/efi_stub.S')
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diff --git a/arch/i386/kernel/efi_stub.S b/arch/i386/kernel/efi_stub.S
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+/*
+ * EFI call stub for IA32.
+ *
+ * This stub allows us to make EFI calls in physical mode with interrupts
+ * turned off.
+ */
+
+#include <linux/config.h>
+#include <linux/linkage.h>
+#include <asm/page.h>
+#include <asm/pgtable.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