[libflat] Remove now-obsolete flatten_real_mode call

Flat real mode will have been set up as a side-effect of the
protected-mode call invoked during install_block() for .text16.early;
there is no need to do so explicitly.

Signed-off-by: Michael Brown <mcb30@ipxe.org>

diff --git a/src/arch/i386/prefix/libprefix.S b/src/arch/i386/prefix/libprefix.S
index c8fbe95bead7b6440f373c092f25e49860d1ec84..f95a7a1ff7e233f567eb57294cfd905fc80a68b4 100644 (file)
--- a/src/arch/i386/prefix/libprefix.S
+++ b/src/arch/i386/prefix/libprefix.S
@@ -649,7 +649,10 @@ install_prealloc:
        popl    %esi
 
 #ifndef KEEP_IT_REAL
-       /* Access high memory */
+       /* Access high memory by enabling the A20 gate.  (We will
+        * already have 4GB segment limits as a result of calling
+        * install_block.)
+        */
        pushw   %cs
        pushw   $1f
        pushw   %ax

diff --git a/src/arch/i386/transitions/libflat.S b/src/arch/i386/transitions/libflat.S
index 98f6f4df6c7a1a5fb8ca37c818ccd9184cae8394..594d62010be04cd68d7258fc6086224fb9e32db5 100644 (file)
--- a/src/arch/i386/transitions/libflat.S
+++ b/src/arch/i386/transitions/libflat.S
@@ -21,124 +21,6 @@ FILE_LICENCE ( GPL2_OR_LATER )
 
        .arch i386
 
-#define CR0_PE 1
-
-/****************************************************************************
- * flatten_real_mode
- *
- * Set up 4GB segment limits
- *
- * Parameters:
- *   none
- * Returns:
- *   none
- * Corrupts:
- *   none
- ****************************************************************************
- */
-       /* GDT for protected-mode calls */
-       .section ".text16.early.data", "aw", @progbits
-       .align 16
-flatten_gdt:
-flatten_gdt_limit:     .word flatten_gdt_length - 1
-flatten_gdt_base:      .long 0
-                       .word 0 /* padding */
-flatten_cs:    /* 16-bit protected-mode flat code segment */
-       .equ    FLAT_CS, flatten_cs - flatten_gdt
-       .word   0xffff, 0
-       .byte   0, 0x9b, 0x8f, 0
-flatten_ss:    /* 16-bit protected-mode flat stack segment */
-       .equ    FLAT_SS, flatten_ss - flatten_gdt
-       .word   0xffff, 0
-       .byte   0, 0x93, 0x8f, 0
-flatten_gdt_end:
-       .equ    flatten_gdt_length, . - flatten_gdt
-       .size   flatten_gdt, . - flatten_gdt
-
-       .section ".text16.early.data", "aw", @progbits
-       .align 16
-flatten_saved_gdt:
-       .long   0, 0
-       .size   flatten_saved_gdt, . - flatten_saved_gdt
-
-       .section ".text16.early", "awx", @progbits
-       .code16
-flatten_real_mode:
-       /* Preserve registers and flags */
-       pushfl
-       pushl   %eax
-       pushw   %si
-       pushw   %gs
-       pushw   %fs
-       pushw   %es
-       pushw   %ds
-       pushw   %ss
-
-       /* Set %ds for access to .text16.early.data variables */
-       pushw   %cs
-       popw    %ds
-
-       /* Preserve original GDT */
-       sgdt flatten_saved_gdt
-
-       /* Set up GDT bases */
-       xorl    %eax, %eax
-       movw    %cs, %ax
-       shll    $4, %eax
-       addl    $flatten_gdt, %eax
-       movl    %eax, flatten_gdt_base
-       movw    %cs, %ax
-       movw    $flatten_cs, %si
-       call    set_seg_base
-       movw    %ss, %ax
-       movw    $flatten_ss, %si
-       call    set_seg_base
-
-       /* Switch temporarily to protected mode and set segment registers */
-       pushw   %cs
-       pushw   $2f
-       cli
-       data32 lgdt flatten_gdt
-       movl    %cr0, %eax
-       orb     $CR0_PE, %al
-       movl    %eax, %cr0
-       ljmp    $FLAT_CS, $1f
-1:     movw    $FLAT_SS, %ax
-       movw    %ax, %ss
-       movw    %ax, %ds
-       movw    %ax, %es
-       movw    %ax, %fs
-       movw    %ax, %gs
-       movl    %cr0, %eax
-       andb    $0!CR0_PE, %al
-       movl    %eax, %cr0
-       lret
-2:     /* lret will ljmp to here */
-
-       /* Restore GDT, registers and flags */
-       data32 lgdt flatten_saved_gdt
-       popw    %ss
-       popw    %ds
-       popw    %es
-       popw    %fs
-       popw    %gs
-       popw    %si
-       popl    %eax
-       popfl
-       ret
-       .size flatten_real_mode, . - flatten_real_mode
-
-       .section ".text16.early", "awx", @progbits
-       .code16
-set_seg_base:
-       rolw    $4, %ax
-       movw    %ax, 2(%si)
-       andw    $0xfff0, 2(%si)
-       movb    %al, 4(%si)
-       andb    $0x0f, 4(%si)
-       ret
-       .size set_seg_base, . - set_seg_base
-
 /****************************************************************************
  * test_a20_short, test_a20_long
  *
@@ -403,7 +285,7 @@ enable_a20_method:
 /****************************************************************************
  * access_highmem (real mode far call)
  *
- * Open up access to high memory in flat real mode with A20 enabled
+ * Open up access to high memory with A20 enabled
  *
  * Parameters:
  *   none
@@ -419,7 +301,5 @@ enable_a20_method:
 access_highmem:
        /* Enable A20 line */
        call    enable_a20
-       /* Set up 4GB limits */
-       call    flatten_real_mode
        lret
        .size   access_highmem, . - access_highmem