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linux/arch/mips/kernel/unaligned.c

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/*
* Handle unaligned accesses by emulation.
*
* This file is subject to the terms and conditions of the GNU General Public
* License. See the file "COPYING" in the main directory of this archive
* for more details.
*
* Copyright (C) 1996, 1998, 1999, 2002 by Ralf Baechle
* Copyright (C) 1999 Silicon Graphics, Inc.
*
* This file contains exception handler for address error exception with the
* special capability to execute faulting instructions in software. The
* handler does not try to handle the case when the program counter points
* to an address not aligned to a word boundary.
*
* Putting data to unaligned addresses is a bad practice even on Intel where
* only the performance is affected. Much worse is that such code is non-
* portable. Due to several programs that die on MIPS due to alignment
* problems I decided to implement this handler anyway though I originally
* didn't intend to do this at all for user code.
*
* For now I enable fixing of address errors by default to make life easier.
* I however intend to disable this somewhen in the future when the alignment
* problems with user programs have been fixed. For programmers this is the
* right way to go.
*
* Fixing address errors is a per process option. The option is inherited
* across fork(2) and execve(2) calls. If you really want to use the
* option in your user programs - I discourage the use of the software
* emulation strongly - use the following code in your userland stuff:
*
* #include <sys/sysmips.h>
*
* ...
* sysmips(MIPS_FIXADE, x);
* ...
*
* The argument x is 0 for disabling software emulation, enabled otherwise.
*
* Below a little program to play around with this feature.
*
* #include <stdio.h>
* #include <sys/sysmips.h>
*
* struct foo {
* unsigned char bar[8];
* };
*
* main(int argc, char *argv[])
* {
* struct foo x = {0, 1, 2, 3, 4, 5, 6, 7};
* unsigned int *p = (unsigned int *) (x.bar + 3);
* int i;
*
* if (argc > 1)
* sysmips(MIPS_FIXADE, atoi(argv[1]));
*
* printf("*p = %08lx\n", *p);
*
* *p = 0xdeadface;
*
* for(i = 0; i <= 7; i++)
* printf("%02x ", x.bar[i]);
* printf("\n");
* }
*
* Coprocessor loads are not supported; I think this case is unimportant
* in the practice.
*
* TODO: Handle ndc (attempted store to doubleword in uncached memory)
* exception for the R6000.
* A store crossing a page boundary might be executed only partially.
* Undo the partial store in this case.
*/
#include <linux/mm.h>
#include <linux/signal.h>
#include <linux/smp.h>
#include <linux/sched.h>
#include <linux/debugfs.h>
#include <linux/perf_event.h>
#include <asm/asm.h>
#include <asm/branch.h>
#include <asm/byteorder.h>
#include <asm/cop2.h>
#include <asm/inst.h>
#include <asm/uaccess.h>
#define STR(x) __STR(x)
#define __STR(x) #x
enum {
UNALIGNED_ACTION_QUIET,
UNALIGNED_ACTION_SIGNAL,
UNALIGNED_ACTION_SHOW,
};
#ifdef CONFIG_DEBUG_FS
static u32 unaligned_instructions;
static u32 unaligned_action;
#else
#define unaligned_action UNALIGNED_ACTION_QUIET
#endif
extern void show_registers(struct pt_regs *regs);
static void emulate_load_store_insn(struct pt_regs *regs,
void __user *addr, unsigned int __user *pc)
{
union mips_instruction insn;
unsigned long value;
unsigned int res;
perf_sw_event(PERF_COUNT_SW_EMULATION_FAULTS, 1, regs, 0);
/*
* This load never faults.
*/
__get_user(insn.word, pc);
switch (insn.i_format.opcode) {
/*
* These are instructions that a compiler doesn't generate. We
* can assume therefore that the code is MIPS-aware and
* really buggy. Emulating these instructions would break the
* semantics anyway.
*/
case ll_op:
case lld_op:
case sc_op:
case scd_op:
/*
* For these instructions the only way to create an address
* error is an attempted access to kernel/supervisor address
* space.
*/
case ldl_op:
case ldr_op:
case lwl_op:
case lwr_op:
case sdl_op:
case sdr_op:
case swl_op:
case swr_op:
case lb_op:
case lbu_op:
case sb_op:
goto sigbus;
/*
* The remaining opcodes are the ones that are really of interest.
*/
case lh_op:
if (!access_ok(VERIFY_READ, addr, 2))
goto sigbus;
__asm__ __volatile__ (".set\tnoat\n"
#ifdef __BIG_ENDIAN
"1:\tlb\t%0, 0(%2)\n"
"2:\tlbu\t$1, 1(%2)\n\t"
#endif
#ifdef __LITTLE_ENDIAN
"1:\tlb\t%0, 1(%2)\n"
"2:\tlbu\t$1, 0(%2)\n\t"
#endif
"sll\t%0, 0x8\n\t"
"or\t%0, $1\n\t"
"li\t%1, 0\n"
"3:\t.set\tat\n\t"
".section\t.fixup,\"ax\"\n\t"
"4:\tli\t%1, %3\n\t"
"j\t3b\n\t"
".previous\n\t"
".section\t__ex_table,\"a\"\n\t"
STR(PTR)"\t1b, 4b\n\t"
STR(PTR)"\t2b, 4b\n\t"
".previous"
: "=&r" (value), "=r" (res)
: "r" (addr), "i" (-EFAULT));
if (res)
goto fault;
compute_return_epc(regs);
regs->regs[insn.i_format.rt] = value;
break;
case lw_op:
if (!access_ok(VERIFY_READ, addr, 4))
goto sigbus;
__asm__ __volatile__ (
#ifdef __BIG_ENDIAN
"1:\tlwl\t%0, (%2)\n"
"2:\tlwr\t%0, 3(%2)\n\t"
#endif
#ifdef __LITTLE_ENDIAN
"1:\tlwl\t%0, 3(%2)\n"
"2:\tlwr\t%0, (%2)\n\t"
#endif
"li\t%1, 0\n"
"3:\t.section\t.fixup,\"ax\"\n\t"
"4:\tli\t%1, %3\n\t"
"j\t3b\n\t"
".previous\n\t"
".section\t__ex_table,\"a\"\n\t"
STR(PTR)"\t1b, 4b\n\t"
STR(PTR)"\t2b, 4b\n\t"
".previous"
: "=&r" (value), "=r" (res)
: "r" (addr), "i" (-EFAULT));
if (res)
goto fault;
compute_return_epc(regs);
regs->regs[insn.i_format.rt] = value;
break;
case lhu_op:
if (!access_ok(VERIFY_READ, addr, 2))
goto sigbus;
__asm__ __volatile__ (
".set\tnoat\n"
#ifdef __BIG_ENDIAN
"1:\tlbu\t%0, 0(%2)\n"
"2:\tlbu\t$1, 1(%2)\n\t"
#endif
#ifdef __LITTLE_ENDIAN
"1:\tlbu\t%0, 1(%2)\n"
"2:\tlbu\t$1, 0(%2)\n\t"
#endif
"sll\t%0, 0x8\n\t"
"or\t%0, $1\n\t"
"li\t%1, 0\n"
"3:\t.set\tat\n\t"
".section\t.fixup,\"ax\"\n\t"
"4:\tli\t%1, %3\n\t"
"j\t3b\n\t"
".previous\n\t"
".section\t__ex_table,\"a\"\n\t"
STR(PTR)"\t1b, 4b\n\t"
STR(PTR)"\t2b, 4b\n\t"
".previous"
: "=&r" (value), "=r" (res)
: "r" (addr), "i" (-EFAULT));
if (res)
goto fault;
compute_return_epc(regs);
regs->regs[insn.i_format.rt] = value;
break;
case lwu_op:
#ifdef CONFIG_64BIT
/*
* A 32-bit kernel might be running on a 64-bit processor. But
* if we're on a 32-bit processor and an i-cache incoherency
* or race makes us see a 64-bit instruction here the sdl/sdr
* would blow up, so for now we don't handle unaligned 64-bit
* instructions on 32-bit kernels.
*/
if (!access_ok(VERIFY_READ, addr, 4))
goto sigbus;
__asm__ __volatile__ (
#ifdef __BIG_ENDIAN
"1:\tlwl\t%0, (%2)\n"
"2:\tlwr\t%0, 3(%2)\n\t"
#endif
#ifdef __LITTLE_ENDIAN
"1:\tlwl\t%0, 3(%2)\n"
"2:\tlwr\t%0, (%2)\n\t"
#endif
"dsll\t%0, %0, 32\n\t"
"dsrl\t%0, %0, 32\n\t"
"li\t%1, 0\n"
"3:\t.section\t.fixup,\"ax\"\n\t"
"4:\tli\t%1, %3\n\t"
"j\t3b\n\t"
".previous\n\t"
".section\t__ex_table,\"a\"\n\t"
STR(PTR)"\t1b, 4b\n\t"
STR(PTR)"\t2b, 4b\n\t"
".previous"
: "=&r" (value), "=r" (res)
: "r" (addr), "i" (-EFAULT));
if (res)
goto fault;
compute_return_epc(regs);
regs->regs[insn.i_format.rt] = value;
break;
#endif /* CONFIG_64BIT */
/* Cannot handle 64-bit instructions in 32-bit kernel */
goto sigill;
case ld_op:
#ifdef CONFIG_64BIT
/*
* A 32-bit kernel might be running on a 64-bit processor. But
* if we're on a 32-bit processor and an i-cache incoherency
* or race makes us see a 64-bit instruction here the sdl/sdr
* would blow up, so for now we don't handle unaligned 64-bit
* instructions on 32-bit kernels.
*/
if (!access_ok(VERIFY_READ, addr, 8))
goto sigbus;
__asm__ __volatile__ (
#ifdef __BIG_ENDIAN
"1:\tldl\t%0, (%2)\n"
"2:\tldr\t%0, 7(%2)\n\t"
#endif
#ifdef __LITTLE_ENDIAN
"1:\tldl\t%0, 7(%2)\n"
"2:\tldr\t%0, (%2)\n\t"
#endif
"li\t%1, 0\n"
"3:\t.section\t.fixup,\"ax\"\n\t"
"4:\tli\t%1, %3\n\t"
"j\t3b\n\t"
".previous\n\t"
".section\t__ex_table,\"a\"\n\t"
STR(PTR)"\t1b, 4b\n\t"
STR(PTR)"\t2b, 4b\n\t"
".previous"
: "=&r" (value), "=r" (res)
: "r" (addr), "i" (-EFAULT));
if (res)
goto fault;
compute_return_epc(regs);
regs->regs[insn.i_format.rt] = value;
break;
#endif /* CONFIG_64BIT */
/* Cannot handle 64-bit instructions in 32-bit kernel */
goto sigill;
case sh_op:
if (!access_ok(VERIFY_WRITE, addr, 2))
goto sigbus;
value = regs->regs[insn.i_format.rt];
__asm__ __volatile__ (
#ifdef __BIG_ENDIAN
".set\tnoat\n"
"1:\tsb\t%1, 1(%2)\n\t"
"srl\t$1, %1, 0x8\n"
"2:\tsb\t$1, 0(%2)\n\t"
".set\tat\n\t"
#endif
#ifdef __LITTLE_ENDIAN
".set\tnoat\n"
"1:\tsb\t%1, 0(%2)\n\t"
"srl\t$1,%1, 0x8\n"
"2:\tsb\t$1, 1(%2)\n\t"
".set\tat\n\t"
#endif
"li\t%0, 0\n"
"3:\n\t"
".section\t.fixup,\"ax\"\n\t"
"4:\tli\t%0, %3\n\t"
"j\t3b\n\t"
".previous\n\t"
".section\t__ex_table,\"a\"\n\t"
STR(PTR)"\t1b, 4b\n\t"
STR(PTR)"\t2b, 4b\n\t"
".previous"
: "=r" (res)
: "r" (value), "r" (addr), "i" (-EFAULT));
if (res)
goto fault;
compute_return_epc(regs);
break;
case sw_op:
if (!access_ok(VERIFY_WRITE, addr, 4))
goto sigbus;
value = regs->regs[insn.i_format.rt];
__asm__ __volatile__ (
#ifdef __BIG_ENDIAN
"1:\tswl\t%1,(%2)\n"
"2:\tswr\t%1, 3(%2)\n\t"
#endif
#ifdef __LITTLE_ENDIAN
"1:\tswl\t%1, 3(%2)\n"
"2:\tswr\t%1, (%2)\n\t"
#endif
"li\t%0, 0\n"
"3:\n\t"
".section\t.fixup,\"ax\"\n\t"
"4:\tli\t%0, %3\n\t"
"j\t3b\n\t"
".previous\n\t"
".section\t__ex_table,\"a\"\n\t"
STR(PTR)"\t1b, 4b\n\t"
STR(PTR)"\t2b, 4b\n\t"
".previous"
: "=r" (res)
: "r" (value), "r" (addr), "i" (-EFAULT));
if (res)
goto fault;
compute_return_epc(regs);
break;
case sd_op:
#ifdef CONFIG_64BIT
/*
* A 32-bit kernel might be running on a 64-bit processor. But
* if we're on a 32-bit processor and an i-cache incoherency
* or race makes us see a 64-bit instruction here the sdl/sdr
* would blow up, so for now we don't handle unaligned 64-bit
* instructions on 32-bit kernels.
*/
if (!access_ok(VERIFY_WRITE, addr, 8))
goto sigbus;
value = regs->regs[insn.i_format.rt];
__asm__ __volatile__ (
#ifdef __BIG_ENDIAN
"1:\tsdl\t%1,(%2)\n"
"2:\tsdr\t%1, 7(%2)\n\t"
#endif
#ifdef __LITTLE_ENDIAN
"1:\tsdl\t%1, 7(%2)\n"
"2:\tsdr\t%1, (%2)\n\t"
#endif
"li\t%0, 0\n"
"3:\n\t"
".section\t.fixup,\"ax\"\n\t"
"4:\tli\t%0, %3\n\t"
"j\t3b\n\t"
".previous\n\t"
".section\t__ex_table,\"a\"\n\t"
STR(PTR)"\t1b, 4b\n\t"
STR(PTR)"\t2b, 4b\n\t"
".previous"
: "=r" (res)
: "r" (value), "r" (addr), "i" (-EFAULT));
if (res)
goto fault;
compute_return_epc(regs);
break;
#endif /* CONFIG_64BIT */
/* Cannot handle 64-bit instructions in 32-bit kernel */
goto sigill;
case lwc1_op:
case ldc1_op:
case swc1_op:
case sdc1_op:
/*
* I herewith declare: this does not happen. So send SIGBUS.
*/
goto sigbus;
/*
* COP2 is available to implementor for application specific use.
* It's up to applications to register a notifier chain and do
* whatever they have to do, including possible sending of signals.
*/
case lwc2_op:
cu2_notifier_call_chain(CU2_LWC2_OP, regs);
break;
case ldc2_op:
cu2_notifier_call_chain(CU2_LDC2_OP, regs);
break;
case swc2_op:
cu2_notifier_call_chain(CU2_SWC2_OP, regs);
break;
case sdc2_op:
cu2_notifier_call_chain(CU2_SDC2_OP, regs);
break;
default:
/*
* Pheeee... We encountered an yet unknown instruction or
* cache coherence problem. Die sucker, die ...
*/
goto sigill;
}
#ifdef CONFIG_DEBUG_FS
unaligned_instructions++;
#endif
return;
fault:
/* Did we have an exception handler installed? */
if (fixup_exception(regs))
return;
die_if_kernel("Unhandled kernel unaligned access", regs);
force_sig(SIGSEGV, current);
return;
sigbus:
die_if_kernel("Unhandled kernel unaligned access", regs);
force_sig(SIGBUS, current);
return;
sigill:
die_if_kernel("Unhandled kernel unaligned access or invalid instruction", regs);
force_sig(SIGILL, current);
}
asmlinkage void do_ade(struct pt_regs *regs)
{
unsigned int __user *pc;
mm_segment_t seg;
perf_sw_event(PERF_COUNT_SW_ALIGNMENT_FAULTS,
1, regs, regs->cp0_badvaddr);
/*
* Did we catch a fault trying to load an instruction?
* Or are we running in MIPS16 mode?
*/
if ((regs->cp0_badvaddr == regs->cp0_epc) || (regs->cp0_epc & 0x1))
goto sigbus;
pc = (unsigned int __user *) exception_epc(regs);
if (user_mode(regs) && !test_thread_flag(TIF_FIXADE))
goto sigbus;
if (unaligned_action == UNALIGNED_ACTION_SIGNAL)
goto sigbus;
else if (unaligned_action == UNALIGNED_ACTION_SHOW)
show_registers(regs);
/*
* Do branch emulation only if we didn't forward the exception.
* This is all so but ugly ...
*/
seg = get_fs();
if (!user_mode(regs))
set_fs(KERNEL_DS);
emulate_load_store_insn(regs, (void __user *)regs->cp0_badvaddr, pc);
set_fs(seg);
return;
sigbus:
die_if_kernel("Kernel unaligned instruction access", regs);
force_sig(SIGBUS, current);
/*
* XXX On return from the signal handler we should advance the epc
*/
}
#ifdef CONFIG_DEBUG_FS
extern struct dentry *mips_debugfs_dir;
static int __init debugfs_unaligned(void)
{
struct dentry *d;
if (!mips_debugfs_dir)
return -ENODEV;
d = debugfs_create_u32("unaligned_instructions", S_IRUGO,
mips_debugfs_dir, &unaligned_instructions);
if (!d)
return -ENOMEM;
d = debugfs_create_u32("unaligned_action", S_IRUGO | S_IWUSR,
mips_debugfs_dir, &unaligned_action);
if (!d)
return -ENOMEM;
return 0;
}
__initcall(debugfs_unaligned);
#endif
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