| /* |
| * AT_SYSINFO entry point |
| */ |
| |
| #include <linux/linkage.h> |
| #include <asm/dwarf2.h> |
| #include <asm/cpufeatures.h> |
| #include <asm/alternative-asm.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 eludicate 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 |
| GLOBAL(int80_landing_pad) |
| |
| /* |
| * 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 |
