diff options
author | 2015-08-28 09:58:54 +0800 | |
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committer | 2015-09-01 12:44:00 +0800 | |
commit | e44e3482bdb4d0ebde2d8b41830ac2cdb07948fb (patch) | |
tree | 66b09f592c55df2878107a468a91d21506104d3f /qemu/roms/openbios/arch/amd64/switch.S | |
parent | 9ca8dbcc65cfc63d6f5ef3312a33184e1d726e00 (diff) |
Add qemu 2.4.0
Change-Id: Ic99cbad4b61f8b127b7dc74d04576c0bcbaaf4f5
Signed-off-by: Yang Zhang <yang.z.zhang@intel.com>
Diffstat (limited to 'qemu/roms/openbios/arch/amd64/switch.S')
-rw-r--r-- | qemu/roms/openbios/arch/amd64/switch.S | 116 |
1 files changed, 116 insertions, 0 deletions
diff --git a/qemu/roms/openbios/arch/amd64/switch.S b/qemu/roms/openbios/arch/amd64/switch.S new file mode 100644 index 000000000..66668150d --- /dev/null +++ b/qemu/roms/openbios/arch/amd64/switch.S @@ -0,0 +1,116 @@ + .globl entry, __switch_context, __exit_context, halt + + .text + .align 4 + +/* + * Entry point + * We start execution from here. + * It is assumed that CPU is in 32-bit protected mode and + * all segments are 4GB and base zero (flat model). + */ +entry: + /* Save boot context and switch to our main context. + * Main context is statically defined in C. + */ + pushl %cs + call __switch_context + + /* We get here when the main context switches back to + * the boot context. + * Return to previous bootloader. + */ + ret + +/* + * Switch execution context + * This saves registers, segments, and GDT in the stack, then + * switches the stack, and restores everything from the new stack. + * This function takes no argument. New stack pointer is + * taken from global variable __context, and old stack pointer + * is also saved to __context. This way we can just jump to + * this routine to get back to the original context. + * + * Call this routine with lcall or pushl %cs; call. + */ +__switch_context: + /* Save everything in current stack */ + pushfl /* 56 */ + pushl %ds /* 52 */ + pushl %es /* 48 */ + pushl %fs /* 44 */ + pushl %gs /* 40 */ + pushal /* 8 */ + subl $8, %esp + movw %ss, (%esp) /* 0 */ + sgdt 2(%esp) /* 2 */ + +#if 0 + /* Swap %cs and %eip on the stack, so lret will work */ + movl 60(%esp), %eax + xchgl %eax, 64(%esp) + movl %eax, 60(%esp) +#endif + + /* At this point we don't know if we are on flat segment + * or relocated. So compute the address offset from %eip. + * Assuming CS.base==DS.base==SS.base. + */ + call 1f +1: popl %ebx + subl $1b, %ebx + + /* Interrupts are not allowed... */ + cli + + /* Current context pointer is our stack pointer */ + movl %esp, %esi + + /* Normalize the ctx pointer */ + subl %ebx, %esi + + /* Swap it with new value */ + xchgl %esi, __context(%ebx) + + /* Adjust new ctx pointer for current address offset */ + addl %ebx, %esi + + /* Load new %ss and %esp to temporary */ + movzwl (%esi), %edx + movl 20(%esi), %eax + + /* Load new GDT */ + lgdt 2(%esi) + + /* Load new stack segment with new GDT */ + movl %edx, %ss + + /* Set new stack pointer, but we have to adjust it because + * pushal saves %esp value before pushal, and we want the value + * after pushal. + */ + leal -32(%eax), %esp + + /* Load the rest from new stack */ + popal + popl %gs + popl %fs + popl %es + popl %ds + popfl + + /* Finally, load new %cs and %eip */ + lret + +__exit_context: + /* Get back to the original context */ + pushl %cs + call __switch_context + + /* We get here if the other context attempt to switch to this + * dead context. This should not happen. */ + +halt: + cli + hlt + jmp halt |