| Andy Lutomirski | e22438f | 2015-04-24 15:09:19 -0700 | [diff] [blame] | 1 | /* |
| 2 | * thunks.S - assembly helpers for mixed-bitness code |
| 3 | * Copyright (c) 2015 Andrew Lutomirski |
| 4 | * |
| 5 | * This program is free software; you can redistribute it and/or modify |
| 6 | * it under the terms and conditions of the GNU General Public License, |
| 7 | * version 2, as published by the Free Software Foundation. |
| 8 | * |
| 9 | * This program is distributed in the hope it will be useful, but |
| 10 | * WITHOUT ANY WARRANTY; without even the implied warranty of |
| 11 | * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU |
| 12 | * General Public License for more details. |
| 13 | * |
| 14 | * These are little helpers that make it easier to switch bitness on |
| 15 | * the fly. |
| 16 | */ |
| 17 | |
| 18 | .text |
| 19 | |
| 20 | .global call32_from_64 |
| 21 | .type call32_from_64, @function |
| 22 | call32_from_64: |
| 23 | // rdi: stack to use |
| 24 | // esi: function to call |
| 25 | |
| 26 | // Save registers |
| 27 | pushq %rbx |
| 28 | pushq %rbp |
| 29 | pushq %r12 |
| 30 | pushq %r13 |
| 31 | pushq %r14 |
| 32 | pushq %r15 |
| 33 | pushfq |
| 34 | |
| 35 | // Switch stacks |
| 36 | mov %rsp,(%rdi) |
| 37 | mov %rdi,%rsp |
| 38 | |
| 39 | // Switch to compatibility mode |
| 40 | pushq $0x23 /* USER32_CS */ |
| 41 | pushq $1f |
| 42 | lretq |
| 43 | |
| 44 | 1: |
| 45 | .code32 |
| 46 | // Call the function |
| 47 | call *%esi |
| 48 | // Switch back to long mode |
| 49 | jmp $0x33,$1f |
| 50 | .code64 |
| 51 | |
| 52 | 1: |
| 53 | // Restore the stack |
| 54 | mov (%rsp),%rsp |
| 55 | |
| 56 | // Restore registers |
| 57 | popfq |
| 58 | popq %r15 |
| 59 | popq %r14 |
| 60 | popq %r13 |
| 61 | popq %r12 |
| 62 | popq %rbp |
| 63 | popq %rbx |
| 64 | |
| 65 | ret |
| 66 | |
| 67 | .size call32_from_64, .-call32_from_64 |