diff options
Diffstat (limited to 'tools/testing/selftests/x86/thunks.S')
| -rw-r--r-- | tools/testing/selftests/x86/thunks.S | 67 |
1 files changed, 67 insertions, 0 deletions
diff --git a/tools/testing/selftests/x86/thunks.S b/tools/testing/selftests/x86/thunks.S new file mode 100644 index 000000000..ce8a995bb --- /dev/null +++ b/tools/testing/selftests/x86/thunks.S @@ -0,0 +1,67 @@ +/* + * thunks.S - assembly helpers for mixed-bitness code + * Copyright (c) 2015 Andrew Lutomirski + * + * This program is free software; you can redistribute it and/or modify + * it under the terms and conditions of the GNU General Public License, + * version 2, as published by the Free Software Foundation. + * + * This program is distributed in the hope it will be useful, but + * WITHOUT ANY WARRANTY; without even the implied warranty of + * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU + * General Public License for more details. + * + * 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 |