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