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/*
* AT_SYSINFO entry point
*/
#include <asm/dwarf2.h>
#include <asm/cpufeature.h>
#include <asm/alternative-asm.h>
/*
* First get the common code for the sigreturn entry points.
* This must come first.
*/
#include "sigreturn.S"
.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
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