/* SPDX-License-Identifier: GPL-2.0 */ /* * AT_SYSINFO entry point */ #include <linux/linkage.h> #include <asm/dwarf2.h> #include <asm/cpufeatures.h> #include <asm/alternative.h> .text .globl __kernel_vsyscall .type __kernel_vsyscall,@function ALIGN __kernel_vsyscall: CFI_STARTPROC /* * Reshuffle regs so that all of any of the entry instructions * will preserve enough state. * * A really nice entry sequence would be: * pushl %edx * pushl %ecx * movl %esp, %ecx * * Unfortunately, naughty Android versions between July and December * 2015 actually hardcode the traditional Linux SYSENTER entry * sequence. That is severely broken for a number of reasons (ask * anyone with an AMD CPU, for example). Nonetheless, we try to keep * it working approximately as well as it ever worked. * * This link may elucidate some of the history: * https://android-review.googlesource.com/#/q/Iac3295376d61ef83e713ac9b528f3b50aa780cd7 * personally, I find it hard to understand what's going on there. * * Note to future user developers: DO NOT USE SYSENTER IN YOUR CODE. * Execute an indirect call to the address in the AT_SYSINFO auxv * entry. That is the ONLY correct way to make a fast 32-bit system * call on Linux. (Open-coding int $0x80 is also fine, but it's * slow.) */ pushl %ecx CFI_ADJUST_CFA_OFFSET 4 CFI_REL_OFFSET ecx, 0 pushl %edx CFI_ADJUST_CFA_OFFSET 4 CFI_REL_OFFSET edx, 0 pushl %ebp CFI_ADJUST_CFA_OFFSET 4 CFI_REL_OFFSET ebp, 0 #define SYSENTER_SEQUENCE "movl %esp, %ebp; sysenter" #define SYSCALL_SEQUENCE "movl %ecx, %ebp; syscall" #ifdef CONFIG_X86_64 /* If SYSENTER (Intel) or SYSCALL32 (AMD) is available, use it. */ ALTERNATIVE_2 "", SYSENTER_SEQUENCE, X86_FEATURE_SYSENTER32, \ SYSCALL_SEQUENCE, X86_FEATURE_SYSCALL32 #else ALTERNATIVE "", SYSENTER_SEQUENCE, X86_FEATURE_SEP #endif /* Enter using int $0x80 */ int $0x80 SYM_INNER_LABEL(int80_landing_pad, SYM_L_GLOBAL) /* * Restore EDX and ECX in case they were clobbered. EBP is not * clobbered (the kernel restores it), but it's cleaner and * probably faster to pop it than to adjust ESP using addl. */ popl %ebp CFI_RESTORE ebp CFI_ADJUST_CFA_OFFSET -4 popl %edx CFI_RESTORE edx CFI_ADJUST_CFA_OFFSET -4 popl %ecx CFI_RESTORE ecx CFI_ADJUST_CFA_OFFSET -4 RET CFI_ENDPROC .size __kernel_vsyscall,.-__kernel_vsyscall .previous