/*
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* thunks.S - assembly helpers for mixed-bitness code
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* Copyright (c) 2015 Andrew Lutomirski
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*
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* This program is free software; you can redistribute it and/or modify
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* it under the terms and conditions of the GNU General Public License,
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* version 2, as published by the Free Software Foundation.
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*
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* This program is distributed in the hope it will be useful, but
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* WITHOUT ANY WARRANTY; without even the implied warranty of
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* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
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* General Public License for more details.
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*
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* These are little helpers that make it easier to switch bitness on
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* the fly.
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*/
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.text
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.global call32_from_64
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.type call32_from_64, @function
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call32_from_64:
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// rdi: stack to use
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// esi: function to call
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// Save registers
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pushq %rbx
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pushq %rbp
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pushq %r12
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pushq %r13
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pushq %r14
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pushq %r15
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pushfq
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// Switch stacks
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mov %rsp,(%rdi)
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mov %rdi,%rsp
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// Switch to compatibility mode
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pushq $0x23 /* USER32_CS */
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pushq $1f
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lretq
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1:
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.code32
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// Call the function
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call *%esi
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// Switch back to long mode
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jmp $0x33,$1f
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.code64
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1:
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// Restore the stack
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mov (%rsp),%rsp
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// Restore registers
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popfq
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popq %r15
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popq %r14
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popq %r13
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popq %r12
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popq %rbp
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popq %rbx
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ret
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.size call32_from_64, .-call32_from_64
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