2 * linux/arch/arm/kernel/swp_emulate.c
4 * Copyright (C) 2009 ARM Limited
5 * __user_* functions adapted from include/asm/uaccess.h
7 * This program is free software; you can redistribute it and/or modify
8 * it under the terms of the GNU General Public License version 2 as
9 * published by the Free Software Foundation.
11 * Implements emulation of the SWP/SWPB instructions using load-exclusive and
12 * store-exclusive for processors that have them disabled (or future ones that
13 * might not implement them).
15 * Syntax of SWP{B} instruction: SWP{B}<c> <Rt>, <Rt2>, [<Rn>]
16 * Where: Rt = destination
21 #include <linux/init.h>
22 #include <linux/kernel.h>
23 #include <linux/proc_fs.h>
24 #include <linux/sched.h>
25 #include <linux/syscalls.h>
26 #include <linux/perf_event.h>
28 #include <asm/opcodes.h>
29 #include <asm/traps.h>
30 #include <asm/uaccess.h>
33 * Error-checking SWP macros implemented using ldrex{b}/strex{b}
35 #define __user_swpX_asm(data, addr, res, temp, B) \
36 __asm__ __volatile__( \
38 "0: ldrex"B" %1, [%3]\n" \
39 "1: strex"B" %0, %2, [%3]\n" \
43 " .section .fixup,\"ax\"\n" \
48 " .section __ex_table,\"a\"\n" \
53 : "=&r" (res), "+r" (data), "=&r" (temp) \
54 : "r" (addr), "i" (-EAGAIN), "i" (-EFAULT) \
57 #define __user_swp_asm(data, addr, res, temp) \
58 __user_swpX_asm(data, addr, res, temp, "")
59 #define __user_swpb_asm(data, addr, res, temp) \
60 __user_swpX_asm(data, addr, res, temp, "b")
63 * Macros/defines for extracting register numbers from instruction.
65 #define EXTRACT_REG_NUM(instruction, offset) \
66 (((instruction) & (0xf << (offset))) >> (offset))
71 * Bit 22 of the instruction encoding distinguishes between
72 * the SWP and SWPB variants (bit set means SWPB).
74 #define TYPE_SWPB (1 << 22)
76 static unsigned long swpcounter
;
77 static unsigned long swpbcounter
;
78 static unsigned long abtcounter
;
79 static pid_t previous_pid
;
82 static int proc_read_status(char *page
, char **start
, off_t off
, int count
,
88 p
+= sprintf(p
, "Emulated SWP:\t\t%lu\n", swpcounter
);
89 p
+= sprintf(p
, "Emulated SWPB:\t\t%lu\n", swpbcounter
);
90 p
+= sprintf(p
, "Aborted SWP{B}:\t\t%lu\n", abtcounter
);
91 if (previous_pid
!= 0)
92 p
+= sprintf(p
, "Last process:\t\t%d\n", previous_pid
);
94 len
= (p
- page
) - off
;
98 *eof
= (len
<= count
) ? 1 : 0;
106 * Set up process info to signal segmentation fault - called on access error.
108 static void set_segfault(struct pt_regs
*regs
, unsigned long addr
)
112 down_read(¤t
->mm
->mmap_sem
);
113 if (find_vma(current
->mm
, addr
) == NULL
)
114 info
.si_code
= SEGV_MAPERR
;
116 info
.si_code
= SEGV_ACCERR
;
117 up_read(¤t
->mm
->mmap_sem
);
119 info
.si_signo
= SIGSEGV
;
121 info
.si_addr
= (void *) instruction_pointer(regs
);
123 pr_debug("SWP{B} emulation: access caused memory abort!\n");
124 arm_notify_die("Illegal memory access", regs
, &info
, 0, 0);
129 static int emulate_swpX(unsigned int address
, unsigned int *data
,
132 unsigned int res
= 0;
134 if ((type
!= TYPE_SWPB
) && (address
& 0x3)) {
135 /* SWP to unaligned address not permitted */
136 pr_debug("SWP instruction on unaligned pointer!\n");
144 * Barrier required between accessing protected resource and
145 * releasing a lock for it. Legacy code might not have done
146 * this, and we cannot determine that this is not the case
147 * being emulated, so insert always.
151 if (type
== TYPE_SWPB
)
152 __user_swpb_asm(*data
, address
, res
, temp
);
154 __user_swp_asm(*data
, address
, res
, temp
);
156 if (likely(res
!= -EAGAIN
) || signal_pending(current
))
164 * Barrier also required between acquiring a lock for a
165 * protected resource and accessing the resource. Inserted for
166 * same reason as above.
170 if (type
== TYPE_SWPB
)
180 * swp_handler logs the id of calling process, dissects the instruction, sanity
181 * checks the memory location, calls emulate_swpX for the actual operation and
182 * deals with fixup/error handling before returning
184 static int swp_handler(struct pt_regs
*regs
, unsigned int instr
)
186 unsigned int address
, destreg
, data
, type
;
187 unsigned int res
= 0;
189 perf_sw_event(PERF_COUNT_SW_EMULATION_FAULTS
, 1, regs
, regs
->ARM_pc
);
191 res
= arm_check_condition(instr
, regs
->ARM_cpsr
);
193 case ARM_OPCODE_CONDTEST_PASS
:
195 case ARM_OPCODE_CONDTEST_FAIL
:
196 /* Condition failed - return to next instruction */
199 case ARM_OPCODE_CONDTEST_UNCOND
:
200 /* If unconditional encoding - not a SWP, undef */
206 if (current
->pid
!= previous_pid
) {
207 pr_debug("\"%s\" (%ld) uses deprecated SWP{B} instruction\n",
208 current
->comm
, (unsigned long)current
->pid
);
209 previous_pid
= current
->pid
;
212 address
= regs
->uregs
[EXTRACT_REG_NUM(instr
, RN_OFFSET
)];
213 data
= regs
->uregs
[EXTRACT_REG_NUM(instr
, RT2_OFFSET
)];
214 destreg
= EXTRACT_REG_NUM(instr
, RT_OFFSET
);
216 type
= instr
& TYPE_SWPB
;
218 pr_debug("addr in r%d->0x%08x, dest is r%d, source in r%d->0x%08x)\n",
219 EXTRACT_REG_NUM(instr
, RN_OFFSET
), address
,
220 destreg
, EXTRACT_REG_NUM(instr
, RT2_OFFSET
), data
);
222 /* Check access in reasonable access range for both SWP and SWPB */
223 if (!access_ok(VERIFY_WRITE
, (address
& ~3), 4)) {
224 pr_debug("SWP{B} emulation: access to %p not allowed!\n",
228 res
= emulate_swpX(address
, &data
, type
);
233 * On successful emulation, revert the adjustment to the PC
234 * made in kernel/traps.c in order to resume execution at the
235 * instruction following the SWP{B}.
238 regs
->uregs
[destreg
] = data
;
239 } else if (res
== -EFAULT
) {
241 * Memory errors do not mean emulation failed.
242 * Set up signal info to return SEGV, then return OK
244 set_segfault(regs
, address
);
251 * Only emulate SWP/SWPB executed in ARM state/User mode.
252 * The kernel must be SWP free and SWP{B} does not exist in Thumb/ThumbEE.
254 static struct undef_hook swp_hook
= {
255 .instr_mask
= 0x0fb00ff0,
256 .instr_val
= 0x01000090,
257 .cpsr_mask
= MODE_MASK
| PSR_T_BIT
| PSR_J_BIT
,
258 .cpsr_val
= USR_MODE
,
263 * Register handler and create status file in /proc/cpu
264 * Invoked as late_initcall, since not needed before init spawned.
266 static int __init
swp_emulation_init(void)
268 #ifdef CONFIG_PROC_FS
269 struct proc_dir_entry
*res
;
271 res
= create_proc_entry("cpu/swp_emulation", S_IRUGO
, NULL
);
276 res
->read_proc
= proc_read_status
;
277 #endif /* CONFIG_PROC_FS */
279 printk(KERN_NOTICE
"Registering SWP/SWPB emulation handler\n");
280 register_undef_hook(&swp_hook
);
285 late_initcall(swp_emulation_init
);