[prefix] Move flatten_real_mode to .text16.early

The flatten_real_mode routine is not needed until after decompressing
.text16.early, and currently performs various contortions to
compensate for the fact that .prefix may not be writable.  Move
flatten_real_mode to .text16.early to save on (compressed) binary size
and simplify the code.

Signed-off-by: Michael Brown <mcb30@ipxe.org>
Signed-off-by: Stefan Hajnoczi <stefanha@gmail.com>

diff --git a/src/arch/i386/prefix/libprefix.S b/src/arch/i386/prefix/libprefix.S
index b820f2a..d7cad05 100644 (file)
--- a/src/arch/i386/prefix/libprefix.S
+++ b/src/arch/i386/prefix/libprefix.S
@@ -233,7 +233,7 @@ print_kill_line:
        .size   print_kill_line, . - print_kill_line
 
 /****************************************************************************
        .size   print_kill_line, . - print_kill_line
 
 /****************************************************************************

- * flatten_real_mode
+ * flatten_real_mode (real-mode far call)

  *
  * Set up 4GB segment limits
  *
  *
  * Set up 4GB segment limits
  *


@@ -248,9 +248,8 @@ print_kill_line:
 #ifndef KEEP_IT_REAL
 
        /* GDT for protected-mode calls */
 #ifndef KEEP_IT_REAL
 
        /* GDT for protected-mode calls */

-       .section ".prefix.lib", "awx", @progbits
+       .section ".text16.early.data", "aw", @progbits

        .align 16
        .align 16

-flatten_vars:

 flatten_gdt:
 flatten_gdt_limit:     .word flatten_gdt_length - 1
 flatten_gdt_base:      .long 0
 flatten_gdt:
 flatten_gdt_limit:     .word flatten_gdt_length - 1
 flatten_gdt_base:      .long 0


@@ -267,62 +266,50 @@ flatten_gdt_end:
        .equ    flatten_gdt_length, . - flatten_gdt
        .size   flatten_gdt, . - flatten_gdt
 
        .equ    flatten_gdt_length, . - flatten_gdt
        .size   flatten_gdt, . - flatten_gdt
 

-       .section ".prefix.lib", "awx", @progbits
+       .section ".text16.early.data", "aw", @progbits

        .align 16
 flatten_saved_gdt:
        .long   0, 0
        .size   flatten_saved_gdt, . - flatten_saved_gdt
 
        .align 16
 flatten_saved_gdt:
        .long   0, 0
        .size   flatten_saved_gdt, . - flatten_saved_gdt
 

-       .equ    flatten_vars_size, . - flatten_vars
-#define FLATTEN_VAR(x) ( -flatten_vars_size + ( (x) - flatten_vars ) )
-
-       .section ".prefix.lib", "awx", @progbits
+       .section ".text16.early", "awx", @progbits

        .code16
 flatten_real_mode:
        .code16
 flatten_real_mode:

-       /* Preserve registers and flags, allocate local variable block */
-       pushw   %bp
-       movw    %sp, %bp
-       subw    $flatten_vars_size, %sp
-       andw    $0xfff0, %sp
+       /* Preserve registers and flags */

        pushfl
        pushl   %eax
        pushfl
        pushl   %eax

-       pushl   %edi

        pushw   %si
        pushw   %si

-       pushw   %cx

        pushw   %gs
        pushw   %fs
        pushw   %es
        pushw   %ds
        pushw   %ss
 
        pushw   %gs
        pushw   %fs
        pushw   %es
        pushw   %ds
        pushw   %ss
 

-       /* Fill local variable block and preserve GDT */
-       pushw   %ss
-       popw    %es
-       movw    $flatten_vars, %si
-       leaw    FLATTEN_VAR(flatten_vars)(%bp), %di
-       movw    $flatten_vars_size, %cx
-       cs rep movsb
-       sgdt    FLATTEN_VAR(flatten_saved_gdt)(%bp)
+       /* 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
 
        /* Set up GDT bases */
        xorl    %eax, %eax

-       movw    %ss, %ax
+       movw    %cs, %ax

        shll    $4, %eax
        shll    $4, %eax

-       movzwl  %bp, %edi
-       addr32 leal FLATTEN_VAR(flatten_gdt)(%eax, %edi), %eax
-       movl    %eax, FLATTEN_VAR(flatten_gdt_base)(%bp)
+       addl    $flatten_gdt, %eax
+       movl    %eax, flatten_gdt_base

        movw    %cs, %ax
        movw    %cs, %ax

-       movw    $FLATTEN_VAR(flatten_cs), %di
+       movw    $flatten_cs, %si

        call    set_seg_base
        movw    %ss, %ax
        call    set_seg_base
        movw    %ss, %ax

-       movw    $FLATTEN_VAR(flatten_ss), %di
+       movw    $flatten_ss, %si

        call    set_seg_base
 
        /* Switch temporarily to protected mode and set segment registers */
        pushw   %cs
        pushw   $2f
        cli
        call    set_seg_base
 
        /* Switch temporarily to protected mode and set segment registers */
        pushw   %cs
        pushw   $2f
        cli

-       data32 lgdt FLATTEN_VAR(flatten_gdt)(%bp)
+       data32 lgdt flatten_gdt

        movl    %cr0, %eax
        orb     $CR0_PE, %al
        movl    %eax, %cr0
        movl    %cr0, %eax
        orb     $CR0_PE, %al
        movl    %eax, %cr0


@@ -340,28 +327,26 @@ flatten_real_mode:
 2:     /* lret will ljmp to here */
 
        /* Restore GDT, registers and flags */
 2:     /* lret will ljmp to here */
 
        /* Restore GDT, registers and flags */

-       data32 lgdt FLATTEN_VAR(flatten_saved_gdt)(%bp)
+       data32 lgdt flatten_saved_gdt

        popw    %ss
        popw    %ds
        popw    %es
        popw    %fs
        popw    %gs
        popw    %ss
        popw    %ds
        popw    %es
        popw    %fs
        popw    %gs

-       popw    %cx

        popw    %si
        popw    %si

-       popl    %edi

        popl    %eax
        popfl
        popl    %eax
        popfl

-       movw    %bp, %sp
-       popw    %bp
-       ret
+       lret

        .size flatten_real_mode, . - flatten_real_mode
 
        .size flatten_real_mode, . - flatten_real_mode
 

+       .section ".text16.early", "awx", @progbits
+       .code16

 set_seg_base:
        rolw    $4, %ax
 set_seg_base:
        rolw    $4, %ax

-       movw    %ax, 2(%bp,%di)
-       andw    $0xfff0, 2(%bp,%di)
-       movb    %al, 4(%bp,%di)
-       andb    $0x0f, 4(%bp,%di)
+       movw    %ax, 2(%si)
+       andw    $0xfff0, 2(%si)
+       movb    %al, 4(%si)
+       andb    $0x0f, 4(%si)

        ret
        .size set_seg_base, . - set_seg_base
 
        ret
        .size set_seg_base, . - set_seg_base
 


@@ -650,7 +635,12 @@ install_prealloc:
        /* Open up access to payload */
 #ifndef KEEP_IT_REAL
        /* Flatten real mode */
        /* Open up access to payload */
 #ifndef KEEP_IT_REAL
        /* Flatten real mode */

-       call    flatten_real_mode
+       pushw   %cs
+       pushw   $1f
+       pushw   %ax
+       pushw   $flatten_real_mode
+       lret
+1:

 #endif
 
        /* Calculate physical address of payload (i.e. first source) */
 #endif
 
        /* Calculate physical address of payload (i.e. first source) */