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| author | Michael Brown | 2007-01-09 15:13:06 +0100 |
|---|---|---|
| committer | Michael Brown | 2007-01-09 15:13:06 +0100 |
| commit | a9369bb50369ca38731ccc3edfa449b9909b4753 (patch) | |
| tree | f8fea34c1d8bd2f31e5782819a590e806bc01ae6 /src/arch/i386/transitions/librm.S | |
| parent | Define "connected" as (diff) | |
| download | ipxe-a9369bb50369ca38731ccc3edfa449b9909b4753.tar.gz ipxe-a9369bb50369ca38731ccc3edfa449b9909b4753.tar.xz ipxe-a9369bb50369ca38731ccc3edfa449b9909b4753.zip | |
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().
Diffstat (limited to 'src/arch/i386/transitions/librm.S')
| -rw-r--r-- | src/arch/i386/transitions/librm.S | 21 |
1 files changed, 10 insertions, 11 deletions
diff --git a/src/arch/i386/transitions/librm.S b/src/arch/i386/transitions/librm.S index 9edbd473..e916ba57 100644 --- a/src/arch/i386/transitions/librm.S +++ b/src/arch/i386/transitions/librm.S @@ -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 |