Subversion Repositories or1k_soc_on_altera_embedded_dev_kit

/*
 * 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