| David Brazdil | 0f672f6 | 2019-12-10 10:32:29 +0000 | [diff] [blame^] | 1 | /* SPDX-License-Identifier: GPL-2.0-only */ |
| Andrew Scull | b4b6d4a | 2019-01-02 15:54:55 +0000 | [diff] [blame] | 2 | /* |
| 3 | * thunks.S - assembly helpers for mixed-bitness code |
| 4 | * Copyright (c) 2015 Andrew Lutomirski |
| 5 | * |
| Andrew Scull | b4b6d4a | 2019-01-02 15:54:55 +0000 | [diff] [blame] | 6 | * These are little helpers that make it easier to switch bitness on |
| 7 | * the fly. |
| 8 | */ |
| 9 | |
| 10 | .text |
| 11 | |
| 12 | .global call32_from_64 |
| 13 | .type call32_from_64, @function |
| 14 | call32_from_64: |
| 15 | // rdi: stack to use |
| 16 | // esi: function to call |
| 17 | |
| 18 | // Save registers |
| 19 | pushq %rbx |
| 20 | pushq %rbp |
| 21 | pushq %r12 |
| 22 | pushq %r13 |
| 23 | pushq %r14 |
| 24 | pushq %r15 |
| 25 | pushfq |
| 26 | |
| 27 | // Switch stacks |
| 28 | mov %rsp,(%rdi) |
| 29 | mov %rdi,%rsp |
| 30 | |
| 31 | // Switch to compatibility mode |
| 32 | pushq $0x23 /* USER32_CS */ |
| 33 | pushq $1f |
| 34 | lretq |
| 35 | |
| 36 | 1: |
| 37 | .code32 |
| 38 | // Call the function |
| 39 | call *%esi |
| 40 | // Switch back to long mode |
| 41 | jmp $0x33,$1f |
| 42 | .code64 |
| 43 | |
| 44 | 1: |
| 45 | // Restore the stack |
| 46 | mov (%rsp),%rsp |
| 47 | |
| 48 | // Restore registers |
| 49 | popfq |
| 50 | popq %r15 |
| 51 | popq %r14 |
| 52 | popq %r13 |
| 53 | popq %r12 |
| 54 | popq %rbp |
| 55 | popq %rbx |
| 56 | |
| 57 | ret |
| 58 | |
| 59 | .size call32_from_64, .-call32_from_64 |