259 lines
6.6 KiB
C
259 lines
6.6 KiB
C
// SPDX-License-Identifier: GPL-2.0-only
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/*
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* linux/arch/arm/kernel/swp_emulate.c
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*
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* Copyright (C) 2009 ARM Limited
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* __user_* functions adapted from include/asm/uaccess.h
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*
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* Implements emulation of the SWP/SWPB instructions using load-exclusive and
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* store-exclusive for processors that have them disabled (or future ones that
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* might not implement them).
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*
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* Syntax of SWP{B} instruction: SWP{B}<c> <Rt>, <Rt2>, [<Rn>]
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* Where: Rt = destination
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* Rt2 = source
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* Rn = address
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*/
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#include <linux/init.h>
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#include <linux/kernel.h>
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#include <linux/proc_fs.h>
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#include <linux/seq_file.h>
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#include <linux/sched.h>
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#include <linux/sched/mm.h>
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#include <linux/syscalls.h>
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#include <linux/perf_event.h>
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#include <asm/opcodes.h>
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#include <asm/system_info.h>
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#include <asm/traps.h>
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#include <linux/uaccess.h>
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/*
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* Error-checking SWP macros implemented using ldrex{b}/strex{b}
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*/
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#define __user_swpX_asm(data, addr, res, temp, B) \
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__asm__ __volatile__( \
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"0: ldrex"B" %2, [%3]\n" \
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"1: strex"B" %0, %1, [%3]\n" \
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" cmp %0, #0\n" \
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" moveq %1, %2\n" \
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" movne %0, %4\n" \
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"2:\n" \
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" .section .text.fixup,\"ax\"\n" \
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" .align 2\n" \
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"3: mov %0, %5\n" \
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" b 2b\n" \
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" .previous\n" \
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" .section __ex_table,\"a\"\n" \
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" .align 3\n" \
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" .long 0b, 3b\n" \
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" .long 1b, 3b\n" \
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" .previous" \
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: "=&r" (res), "+r" (data), "=&r" (temp) \
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: "r" (addr), "i" (-EAGAIN), "i" (-EFAULT) \
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: "cc", "memory")
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#define __user_swp_asm(data, addr, res, temp) \
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__user_swpX_asm(data, addr, res, temp, "")
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#define __user_swpb_asm(data, addr, res, temp) \
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__user_swpX_asm(data, addr, res, temp, "b")
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/*
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* Macros/defines for extracting register numbers from instruction.
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*/
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#define EXTRACT_REG_NUM(instruction, offset) \
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(((instruction) & (0xf << (offset))) >> (offset))
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#define RN_OFFSET 16
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#define RT_OFFSET 12
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#define RT2_OFFSET 0
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/*
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* Bit 22 of the instruction encoding distinguishes between
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* the SWP and SWPB variants (bit set means SWPB).
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*/
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#define TYPE_SWPB (1 << 22)
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static unsigned long swpcounter;
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static unsigned long swpbcounter;
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static unsigned long abtcounter;
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static pid_t previous_pid;
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#ifdef CONFIG_PROC_FS
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static int proc_status_show(struct seq_file *m, void *v)
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{
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seq_printf(m, "Emulated SWP:\t\t%lu\n", swpcounter);
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seq_printf(m, "Emulated SWPB:\t\t%lu\n", swpbcounter);
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seq_printf(m, "Aborted SWP{B}:\t\t%lu\n", abtcounter);
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if (previous_pid != 0)
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seq_printf(m, "Last process:\t\t%d\n", previous_pid);
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return 0;
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}
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#endif
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/*
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* Set up process info to signal segmentation fault - called on access error.
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*/
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static void set_segfault(struct pt_regs *regs, unsigned long addr)
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{
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int si_code;
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down_read(¤t->mm->mmap_sem);
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if (find_vma(current->mm, addr) == NULL)
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si_code = SEGV_MAPERR;
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else
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si_code = SEGV_ACCERR;
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up_read(¤t->mm->mmap_sem);
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pr_debug("SWP{B} emulation: access caused memory abort!\n");
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arm_notify_die("Illegal memory access", regs,
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SIGSEGV, si_code,
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(void __user *)instruction_pointer(regs),
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0, 0);
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abtcounter++;
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}
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static int emulate_swpX(unsigned int address, unsigned int *data,
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unsigned int type)
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{
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unsigned int res = 0;
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if ((type != TYPE_SWPB) && (address & 0x3)) {
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/* SWP to unaligned address not permitted */
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pr_debug("SWP instruction on unaligned pointer!\n");
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return -EFAULT;
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}
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while (1) {
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unsigned long temp;
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unsigned int __ua_flags;
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__ua_flags = uaccess_save_and_enable();
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if (type == TYPE_SWPB)
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__user_swpb_asm(*data, address, res, temp);
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else
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__user_swp_asm(*data, address, res, temp);
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uaccess_restore(__ua_flags);
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if (likely(res != -EAGAIN) || signal_pending(current))
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break;
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cond_resched();
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}
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if (res == 0) {
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if (type == TYPE_SWPB)
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swpbcounter++;
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else
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swpcounter++;
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}
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return res;
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}
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/*
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* swp_handler logs the id of calling process, dissects the instruction, sanity
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* checks the memory location, calls emulate_swpX for the actual operation and
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* deals with fixup/error handling before returning
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*/
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static int swp_handler(struct pt_regs *regs, unsigned int instr)
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{
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unsigned int address, destreg, data, type;
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unsigned int res = 0;
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perf_sw_event(PERF_COUNT_SW_EMULATION_FAULTS, 1, regs, regs->ARM_pc);
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res = arm_check_condition(instr, regs->ARM_cpsr);
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switch (res) {
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case ARM_OPCODE_CONDTEST_PASS:
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break;
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case ARM_OPCODE_CONDTEST_FAIL:
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/* Condition failed - return to next instruction */
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regs->ARM_pc += 4;
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return 0;
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case ARM_OPCODE_CONDTEST_UNCOND:
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/* If unconditional encoding - not a SWP, undef */
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return -EFAULT;
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default:
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return -EINVAL;
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}
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if (current->pid != previous_pid) {
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pr_debug("\"%s\" (%ld) uses deprecated SWP{B} instruction\n",
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current->comm, (unsigned long)current->pid);
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previous_pid = current->pid;
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}
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address = regs->uregs[EXTRACT_REG_NUM(instr, RN_OFFSET)];
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data = regs->uregs[EXTRACT_REG_NUM(instr, RT2_OFFSET)];
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destreg = EXTRACT_REG_NUM(instr, RT_OFFSET);
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type = instr & TYPE_SWPB;
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pr_debug("addr in r%d->0x%08x, dest is r%d, source in r%d->0x%08x)\n",
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EXTRACT_REG_NUM(instr, RN_OFFSET), address,
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destreg, EXTRACT_REG_NUM(instr, RT2_OFFSET), data);
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/* Check access in reasonable access range for both SWP and SWPB */
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if (!access_ok((address & ~3), 4)) {
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pr_debug("SWP{B} emulation: access to %p not allowed!\n",
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(void *)address);
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res = -EFAULT;
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} else {
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res = emulate_swpX(address, &data, type);
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}
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if (res == 0) {
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/*
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* On successful emulation, revert the adjustment to the PC
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* made in kernel/traps.c in order to resume execution at the
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* instruction following the SWP{B}.
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*/
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regs->ARM_pc += 4;
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regs->uregs[destreg] = data;
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} else if (res == -EFAULT) {
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/*
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* Memory errors do not mean emulation failed.
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* Set up signal info to return SEGV, then return OK
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*/
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set_segfault(regs, address);
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}
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return 0;
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}
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/*
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* Only emulate SWP/SWPB executed in ARM state/User mode.
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* The kernel must be SWP free and SWP{B} does not exist in Thumb/ThumbEE.
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*/
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static struct undef_hook swp_hook = {
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.instr_mask = 0x0fb00ff0,
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.instr_val = 0x01000090,
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.cpsr_mask = MODE_MASK | PSR_T_BIT | PSR_J_BIT,
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.cpsr_val = USR_MODE,
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.fn = swp_handler
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};
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/*
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* Register handler and create status file in /proc/cpu
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* Invoked as late_initcall, since not needed before init spawned.
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*/
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static int __init swp_emulation_init(void)
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{
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if (cpu_architecture() < CPU_ARCH_ARMv7)
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return 0;
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#ifdef CONFIG_PROC_FS
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if (!proc_create_single("cpu/swp_emulation", S_IRUGO, NULL,
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proc_status_show))
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return -ENOMEM;
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#endif /* CONFIG_PROC_FS */
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pr_notice("Registering SWP/SWPB emulation handler\n");
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register_undef_hook(&swp_hook);
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return 0;
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}
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late_initcall(swp_emulation_init);
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