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- /* SPDX-License-Identifier: GPL-2.0-only */
- /*
- * thunks.S - assembly helpers for mixed-bitness code
- * Copyright (c) 2015 Andrew Lutomirski
- *
- * These are little helpers that make it easier to switch bitness on
- * the fly.
- */
- .text
- .global call32_from_64
- .type call32_from_64, @function
- call32_from_64:
- // rdi: stack to use
- // esi: function to call
- // Save registers
- pushq %rbx
- pushq %rbp
- pushq %r12
- pushq %r13
- pushq %r14
- pushq %r15
- pushfq
- // Switch stacks
- mov %rsp,(%rdi)
- mov %rdi,%rsp
- // Switch to compatibility mode
- pushq $0x23 /* USER32_CS */
- pushq $1f
- lretq
- 1:
- .code32
- // Call the function
- call *%esi
- // Switch back to long mode
- jmp $0x33,$1f
- .code64
- 1:
- // Restore the stack
- mov (%rsp),%rsp
- // Restore registers
- popfq
- popq %r15
- popq %r14
- popq %r13
- popq %r12
- popq %rbp
- popq %rbx
- ret
- .size call32_from_64, .-call32_from_64
- .section .note.GNU-stack,"",%progbits
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