projects / deliverable / linux.git / blame
| Commit | Line | Data |
|---|---|---|
| e22438f8 AL |
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 |