projects / linux-2.6-block.git / blame
| Commit | Line | Data |
|---|---|---|
| b2441318 | 1 | /* SPDX-License-Identifier: GPL-2.0 */ |
| 1da177e4 | 2 | /* |
| 6a613ac6 | 3 | * AT_SYSINFO entry point |
| 29c0ce95 AL |
4 | */ |
| 5 | ||
| f0702555 | 6 | #include <linux/linkage.h> |
| 29c0ce95 | 7 | #include <asm/dwarf2.h> |
| cd4d09ec | 8 | #include <asm/cpufeatures.h> |
| a474e67c | 9 | #include <asm/alternative-asm.h> |
| 29c0ce95 | 10 | |
| 1da177e4 LT |
11 | .text |
| 12 | .globl __kernel_vsyscall | |
| 13 | .type __kernel_vsyscall,@function | |
| 69d0627a | 14 | ALIGN |
| 1da177e4 | 15 | __kernel_vsyscall: |
| 29c0ce95 | 16 | CFI_STARTPROC |
| 8242c6c8 AL |
17 | /* |
| 18 | * Reshuffle regs so that all of any of the entry instructions | |
| 19 | * will preserve enough state. | |
| 30bfa7b3 AL |
20 | * |
| 21 | * A really nice entry sequence would be: | |
| 22 | * pushl %edx | |
| 23 | * pushl %ecx | |
| 24 | * movl %esp, %ecx | |
| 25 | * | |
| 26 | * Unfortunately, naughty Android versions between July and December | |
| 27 | * 2015 actually hardcode the traditional Linux SYSENTER entry | |
| 28 | * sequence. That is severely broken for a number of reasons (ask | |
| 29 | * anyone with an AMD CPU, for example). Nonetheless, we try to keep | |
| 30 | * it working approximately as well as it ever worked. | |
| 31 | * | |
| 32 | * This link may eludicate some of the history: | |
| 33 | * https://android-review.googlesource.com/#/q/Iac3295376d61ef83e713ac9b528f3b50aa780cd7 | |
| 34 | * personally, I find it hard to understand what's going on there. | |
| 35 | * | |
| 36 | * Note to future user developers: DO NOT USE SYSENTER IN YOUR CODE. | |
| 37 | * Execute an indirect call to the address in the AT_SYSINFO auxv | |
| 38 | * entry. That is the ONLY correct way to make a fast 32-bit system | |
| 39 | * call on Linux. (Open-coding int $0x80 is also fine, but it's | |
| 40 | * slow.) | |
| 8242c6c8 | 41 | */ |
| 30bfa7b3 AL |
42 | pushl %ecx |
| 43 | CFI_ADJUST_CFA_OFFSET 4 | |
| 44 | CFI_REL_OFFSET ecx, 0 | |
| 8242c6c8 AL |
45 | pushl %edx |
| 46 | CFI_ADJUST_CFA_OFFSET 4 | |
| 47 | CFI_REL_OFFSET edx, 0 | |
| 30bfa7b3 | 48 | pushl %ebp |
| 8242c6c8 | 49 | CFI_ADJUST_CFA_OFFSET 4 |
| 30bfa7b3 AL |
50 | CFI_REL_OFFSET ebp, 0 |
| 51 | ||
| 52 | #define SYSENTER_SEQUENCE "movl %esp, %ebp; sysenter" | |
| 53 | #define SYSCALL_SEQUENCE "movl %ecx, %ebp; syscall" | |
| 8242c6c8 | 54 | |
| a474e67c AL |
55 | #ifdef CONFIG_X86_64 |
| 56 | /* If SYSENTER (Intel) or SYSCALL32 (AMD) is available, use it. */ | |
| 30bfa7b3 AL |
57 | ALTERNATIVE_2 "", SYSENTER_SEQUENCE, X86_FEATURE_SYSENTER32, \ |
| 58 | SYSCALL_SEQUENCE, X86_FEATURE_SYSCALL32 | |
| 5f310f73 | 59 | #else |
| 30bfa7b3 | 60 | ALTERNATIVE "", SYSENTER_SEQUENCE, X86_FEATURE_SEP |
| a474e67c AL |
61 | #endif |
| 62 | ||
| 8242c6c8 | 63 | /* Enter using int $0x80 */ |
| 8242c6c8 | 64 | int $0x80 |
| 26ba4e57 | 65 | SYM_INNER_LABEL(int80_landing_pad, SYM_L_GLOBAL) |
| 8242c6c8 | 66 | |
| 30bfa7b3 AL |
67 | /* |
| 68 | * Restore EDX and ECX in case they were clobbered. EBP is not | |
| 69 | * clobbered (the kernel restores it), but it's cleaner and | |
| 70 | * probably faster to pop it than to adjust ESP using addl. | |
| 71 | */ | |
| 72 | popl %ebp | |
| 73 | CFI_RESTORE ebp | |
| 8242c6c8 AL |
74 | CFI_ADJUST_CFA_OFFSET -4 |
| 75 | popl %edx | |
| 76 | CFI_RESTORE edx | |
| 77 | CFI_ADJUST_CFA_OFFSET -4 | |
| 30bfa7b3 AL |
78 | popl %ecx |
| 79 | CFI_RESTORE ecx | |
| 80 | CFI_ADJUST_CFA_OFFSET -4 | |
| 1da177e4 | 81 | ret |
| 29c0ce95 | 82 | CFI_ENDPROC |
| 1da177e4 | 83 | |
| 29c0ce95 | 84 | .size __kernel_vsyscall,.-__kernel_vsyscall |
| 69d0627a | 85 | .previous |