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Leave protected-mode return address on PM stack when issuing a 

real_call(), rather than moving it to the RM stack and back again.
This allows the real-mode function to completely destroy the stack
contents, provided that it manages to return to real_call().
This commit is contained in:
Michael Brown 2007-01-09 14:13:06 +00:00
parent 2eeb7c4fe7
commit a9369bb503
1 changed files with 10 additions and 11 deletions
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21
src/arch/i386/transitions/librm.S
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@ -455,28 +455,25 @@ prot_call:
.code32
.globl real_call
real_call:
/* Create register dump on PM stack */
/* Create register dump and function pointer copy on PM stack */
pushal
pushl RC_OFFSET_FUNCTION(%esp)
/* Switch to real mode and move register dump to RM stack */
movl $RC_OFFSET_END, %ecx
/* Switch to real mode and move register dump to RM stack */
movl $( RC_OFFSET_RETADDR + 4 /* function pointer copy */ ), %ecx
pushl $1f
jmp prot_to_real
.section ".text16"
.code16
1:
/* Construct call to real-mode function */
movw %sp, %bp
movw RC_OFFSET_FUNCTION(%bp), %ax
movw %ax, rc_function
/* Call real-mode function */
popl rc_function
popal
call *rc_function
pushal
/* Switch to protected mode and move register dump back to PM stack */
movl $RC_OFFSET_END, %ecx
movl $RC_OFFSET_RETADDR, %ecx
pushl $1f
jmp real_to_prot
.section ".text"
@ -487,9 +484,11 @@ real_call:
ret
/* Function vector, used because */
/* Function vector, used because "call xx(%sp)" is not a valid
* 16-bit expression.
*/
.section ".data16"
rc_function: .word 0
rc_function: .word 0, 0
/****************************************************************************
* Stored real-mode and protected-mode stack pointers