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/*
* linux/arch/arm/kernel/idiv_emulate.c
*
* This code is based on swp_emulate.c
*
* This program is free software; you can redistribute it and/or modify
* it under the terms of the GNU General Public License version 2 as
* published by the Free Software Foundation.
*
* Implements emulation of the SDIV/UDIV instructions. They are defined for
* ARMv7-R and ARMv7-M profiles (in Thumb state only) and are UNDEFINED in the
* ARMv7-A profile. SDIV/UDIV are present by default on Cortex-A15.
*
* This emulation allow using integer divide instructions in case hardware is
* not presented
*
* Syntax of SDIV/UDIV instructions: SDIV/UDIV<c> <Rd>,<Rn>,<Rm>
* Where: Rd = the destination register.
* Rn = the register that contains the dividend.
* Rm = the register that contains the divisor.
*/
#include <linux/init.h>
#include <linux/kernel.h>
#include <linux/proc_fs.h>
#include <linux/sched.h>
#include <linux/syscalls.h>
#include <linux/perf_event.h>
#include <asm/opcodes.h>
#include <asm/traps.h>
#include <asm/uaccess.h>
/*
* Macros/defines for extracting register numbers from instruction.
*/
#define EXTRACT_REG_NUM(instruction, offset) \
(((instruction) & (0xf << (offset))) >> (offset))
/*
* Offsets for ARM mode
*/
#define RD_OFFSET 16
#define RN_OFFSET 0
#define RM_OFFSET 8
/*
* Offsets for Thumb mode
*/
#define RD_T_OFFSET 8
#define RN_T_OFFSET 16
#define RM_T_OFFSET 0
#define TYPE_OF_DIV (1 << 21)
static unsigned long sdivcounter;
static unsigned long udivcounter;
static pid_t previous_pid;
#ifdef CONFIG_PROC_FS
static int proc_read_status(char *page, char **start, off_t off, int count,
int *eof, void *data)
{
char *p = page;
int len;
p += sprintf(p, "Emulated UDIV:\t\t%lu\n", udivcounter);
p += sprintf(p, "Emulated SDIV:\t\t%lu\n", sdivcounter);
if (previous_pid != 0)
p += sprintf(p, "Last process:\t\t%d\n", previous_pid);
len = (p - page) - off;
if (len < 0)
len = 0;
*eof = (len <= count) ? 1 : 0;
*start = page + off;
return len;
}
#endif
static u32 emulate_udiv(u32 n, u32 base)
{
udivcounter++;
return n/base;
}
static s32 emulate_sdiv(s32 n, s32 base)
{
sdivcounter++;
return n/base;
}
static int idiv_handler(struct pt_regs *regs, unsigned int instr)
{
long dividend, divisor, dest, res;
perf_sw_event(PERF_COUNT_SW_EMULATION_FAULTS, 1, 0, regs, regs->ARM_pc);
res = arm_check_condition(instr, regs->ARM_cpsr);
switch (res) {
case ARM_OPCODE_CONDTEST_PASS:
break;
case ARM_OPCODE_CONDTEST_FAIL:
/* Condition failed - return to next instruction */
regs->ARM_pc += 4;
return 0;
case ARM_OPCODE_CONDTEST_UNCOND:
if (!thumb_mode(regs))
return -EFAULT;
break;
default:
return -EINVAL;
}
if (current->pid != previous_pid) {
pr_debug("\"%s\" (%ld) uses idiv instruction\n",
current->comm, (unsigned long)current->pid);
previous_pid = current->pid;
}
if (!thumb_mode(regs)) {
dividend = regs->uregs[EXTRACT_REG_NUM(instr, RN_OFFSET)];
divisor = regs->uregs[EXTRACT_REG_NUM(instr, RM_OFFSET)];
dest = EXTRACT_REG_NUM(instr, RD_OFFSET);
} else {
dividend = regs->uregs[EXTRACT_REG_NUM(instr, RN_T_OFFSET)];
divisor = regs->uregs[EXTRACT_REG_NUM(instr, RM_T_OFFSET)];
dest = EXTRACT_REG_NUM(instr, RD_T_OFFSET);
}
/*
* In an ARMv7-A profile implementation that supports the SDIV and UDIV
* instructions, divide-by-zero always returns a zero result.
* In fact, integer division emulation provided by gcc lib has already handle
* division by zero case sending the signal to the caused process. Emulate this
* behavior here as well.
*/
if (!divisor) {
siginfo_t info;
info.si_code = FPE_INTDIV;
info.si_signo = SIGFPE;
info.si_errno = 0;
arm_notify_die("Division by zero", regs, &info, 0, 0);
goto out;
}
if (instr & TYPE_OF_DIV)
res = emulate_udiv((u32)dividend, (u32)divisor);
else
res = emulate_sdiv((s32)dividend, (s32)divisor);
regs->ARM_pc += 4;
regs->uregs[dest] = res;
out:
return 0;
}
static struct undef_hook idiv_hook = {
.instr_mask = 0x0310f010,
.instr_val = 0x0310f010,
.cpsr_mask = MODE_MASK,
.cpsr_val = USR_MODE,
.fn = idiv_handler
};
static int __init idiv_emulation_init(void)
{
#ifdef CONFIG_PROC_FS
struct proc_dir_entry *res;
res = create_proc_entry("cpu/idiv_emulation", S_IRUGO, NULL);
if (!res)
return -ENOMEM;
res->read_proc = proc_read_status;
#endif /* CONFIG_PROC_FS */
pr_notice("Registering SDIV/UDIV emulation handler\n");
register_undef_hook(&idiv_hook);
return 0;
}
late_initcall(idiv_emulation_init);
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