1 /* SPDX-License-Identifier: GPL-2.0 */ 2 /* 3 * AT_SYSINFO entry point 4 */ 5 6 #include <linux/linkage.h> 7 #include <asm/dwarf2.h> 8 #include <asm/cpufeatures.h> 9 #include <asm/alternative.h> 10 11 .text 12 .globl __kernel_vsyscall 13 .type __kernel_vsyscall,@function 14 ALIGN 15 __kernel_vsyscall: 16 CFI_STARTPROC 17 /* 18 * Reshuffle regs so that all of any of the entry instructions 19 * will preserve enough state. 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.) 41 */ 42 pushl %ecx 43 CFI_ADJUST_CFA_OFFSET 4 44 CFI_REL_OFFSET ecx, 0 45 pushl %edx 46 CFI_ADJUST_CFA_OFFSET 4 47 CFI_REL_OFFSET edx, 0 48 pushl %ebp 49 CFI_ADJUST_CFA_OFFSET 4 50 CFI_REL_OFFSET ebp, 0 51 52 #define SYSENTER_SEQUENCE "movl %esp, %ebp; sysenter" 53 #define SYSCALL_SEQUENCE "movl %ecx, %ebp; syscall" 54 55 #ifdef CONFIG_X86_64 56 /* If SYSENTER (Intel) or SYSCALL32 (AMD) is available, use it. */ 57 ALTERNATIVE_2 "", SYSENTER_SEQUENCE, X86_FEATURE_SYSENTER32, \ 58 SYSCALL_SEQUENCE, X86_FEATURE_SYSCALL32 59 #else 60 ALTERNATIVE "", SYSENTER_SEQUENCE, X86_FEATURE_SEP 61 #endif 62 63 /* Enter using int $0x80 */ 64 int $0x80 65 SYM_INNER_LABEL(int80_landing_pad, SYM_L_GLOBAL) 66 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 74 CFI_ADJUST_CFA_OFFSET -4 75 popl %edx 76 CFI_RESTORE edx 77 CFI_ADJUST_CFA_OFFSET -4 78 popl %ecx 79 CFI_RESTORE ecx 80 CFI_ADJUST_CFA_OFFSET -4 81 RET 82 CFI_ENDPROC 83 84 .size __kernel_vsyscall,.-__kernel_vsyscall 85 .previous 86