source: mainline/kernel/arch/ia32/src/context.S@ d6f9fff

#
# Copyright (c) 2001-2004 Jakub Jermar
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#include <abi/asmtool.h>
#include <arch/context_struct.h>
#include <arch/vreg.h>

.text

## Save current CPU context
#
# Save CPU context to the context_t variable
# pointed by the 1st argument. Returns 1 in EAX.
#
FUNCTION_BEGIN(context_save_arch)
        movl 0(%esp), %eax      # save pc value into eax        
        movl 4(%esp), %edx      # address of the context variable to save context to 

        # save registers to given structure
        movl %esp, CONTEXT_OFFSET_SP(%edx)      # %esp -> ctx->sp
        movl %eax, CONTEXT_OFFSET_PC(%edx)      # %eip -> ctx->pc
        movl %ebx, CONTEXT_OFFSET_EBX(%edx)     # %ebx -> ctx->ebx
        movl %esi, CONTEXT_OFFSET_ESI(%edx)     # %esi -> ctx->esi
        movl %edi, CONTEXT_OFFSET_EDI(%edx)     # %edi -> ctx->edi
        movl %ebp, CONTEXT_OFFSET_EBP(%edx)     # %ebp -> ctx->ebp

        mov vreg_ptr, %ecx
        movl %gs:VREG_TP(%ecx), %ecx
        movl %ecx, CONTEXT_OFFSET_TP(%edx)

        xorl %eax, %eax         # context_save returns 1
        incl %eax
        ret
FUNCTION_END(context_save_arch)


## Restore saved CPU context
#
# Restore CPU context from context_t variable
# pointed by the 1st argument. Returns 0 in EAX.
#
FUNCTION_BEGIN(context_restore_arch)
        movl 4(%esp), %eax      # address of the context variable to restore context from

        # restore registers from given structure
        movl CONTEXT_OFFSET_SP(%eax), %esp      # ctx->sp -> %esp
        movl CONTEXT_OFFSET_PC(%eax), %edx      # ctx->pc -> \pc
        movl CONTEXT_OFFSET_EBX(%eax), %ebx     # ctx->ebx -> %ebx
        movl CONTEXT_OFFSET_ESI(%eax), %esi     # ctx->esi -> %esi
        movl CONTEXT_OFFSET_EDI(%eax), %edi     # ctx->edi -> %edi
        movl CONTEXT_OFFSET_EBP(%eax), %ebp     # ctx->ebp -> %ebp

        movl %edx, 0(%esp)      # put saved pc on stack

        mov vreg_ptr, %ecx
        movl CONTEXT_OFFSET_TP(%eax), %edx
        movl %edx, %gs:VREG_TP(%ecx)

        xorl %eax, %eax         # context_restore returns 0
        ret