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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 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 <asm/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/config.h>
#include <linux/mm.h>
#include <linux/signal.h>
#include <linux/smp.h>
#include <linux/smp_lock.h>
#include <asm/asm.h>
#include <asm/branch.h>
#include <asm/byteorder.h>
#include <asm/inst.h>
#include <asm/uaccess.h>
#include <asm/system.h>
#define STR(x) __STR(x)
#define __STR(x) #x
/*
* User code may only access USEG; kernel code may access the
* entire address space.
*/
#define check_axs(pc,a,s) \
if ((long)(~(pc) & ((a) | ((a)+(s)))) < 0) \
goto sigbus;
static inline void
emulate_load_store_insn(struct pt_regs *regs,
unsigned long addr,
unsigned long pc)
{
union mips_instruction insn;
unsigned long value, fixup;
regs->regs[0] = 0;
/*
* This load never faults.
*/
__get_user(insn.word, (unsigned int *)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:
check_axs(pc, addr, 2);
__asm__(
".set\tnoat\n"
#ifdef __BIG_ENDIAN
"1:\tlb\t%0,0(%1)\n"
"2:\tlbu\t$1,1(%1)\n\t"
#endif
#ifdef __LITTLE_ENDIAN
"1:\tlb\t%0,1(%1)\n"
"2:\tlbu\t$1,0(%1)\n\t"
#endif
"sll\t%0,0x8\n\t"
"or\t%0,$1\n\t"
".set\tat\n\t"
".section\t__ex_table,\"a\"\n\t"
STR(PTR)"\t1b,%2\n\t"
STR(PTR)"\t2b,%2\n\t"
".previous"
:"=&r" (value)
:"r" (addr), "i" (&&fault)
:"$1");
regs->regs[insn.i_format.rt] = value;
return;
case lw_op:
check_axs(pc, addr, 4);
__asm__(
#ifdef __BIG_ENDIAN
"1:\tlwl\t%0,(%1)\n"
"2:\tlwr\t%0,3(%1)\n\t"
#endif
#ifdef __LITTLE_ENDIAN
"1:\tlwl\t%0,3(%1)\n"
"2:\tlwr\t%0,(%1)\n\t"
#endif
".section\t__ex_table,\"a\"\n\t"
STR(PTR)"\t1b,%2\n\t"
STR(PTR)"\t2b,%2\n\t"
".previous"
:"=&r" (value)
:"r" (addr), "i" (&&fault));
regs->regs[insn.i_format.rt] = value;
return;
case lhu_op:
check_axs(pc, addr, 2);
__asm__(
".set\tnoat\n"
#ifdef __BIG_ENDIAN
"1:\tlbu\t%0,0(%1)\n"
"2:\tlbu\t$1,1(%1)\n\t"
#endif
#ifdef __LITTLE_ENDIAN
"1:\tlbu\t%0,1(%1)\n"
"2:\tlbu\t$1,0(%1)\n\t"
#endif
"sll\t%0,0x8\n\t"
"or\t%0,$1\n\t"
".set\tat\n\t"
".section\t__ex_table,\"a\"\n\t"
STR(PTR)"\t1b,%2\n\t"
STR(PTR)"\t2b,%2\n\t"
".previous"
:"=&r" (value)
:"r" (addr), "i" (&&fault)
:"$1");
regs->regs[insn.i_format.rt] = value;
return;
case lwu_op:
check_axs(pc, addr, 4);
__asm__(
#ifdef __BIG_ENDIAN
"1:\tlwl\t%0,(%1)\n"
"2:\tlwr\t%0,3(%1)\n\t"
#endif
#ifdef __LITTLE_ENDIAN
"1:\tlwl\t%0,3(%1)\n"
"2:\tlwr\t%0,(%1)\n\t"
#endif
".section\t__ex_table,\"a\"\n\t"
STR(PTR)"\t1b,%2\n\t"
STR(PTR)"\t2b,%2\n\t"
".previous"
:"=&r" (value)
:"r" (addr), "i" (&&fault));
value &= 0xffffffff;
regs->regs[insn.i_format.rt] = value;
return;
case ld_op:
check_axs(pc, addr, 8);
__asm__(
".set\tmips3\n"
#ifdef __BIG_ENDIAN
"1:\tldl\t%0,(%1)\n"
"2:\tldr\t%0,7(%1)\n\t"
#endif
#ifdef __LITTLE_ENDIAN
"1:\tldl\t%0,7(%1)\n"
"2:\tldr\t%0,(%1)\n\t"
#endif
".set\tmips0\n\t"
".section\t__ex_table,\"a\"\n\t"
STR(PTR)"\t1b,%2\n\t"
STR(PTR)"\t2b,%2\n\t"
".previous"
:"=&r" (value)
:"r" (addr), "i" (&&fault));
regs->regs[insn.i_format.rt] = value;
return;
case sh_op:
check_axs(pc, addr, 2);
value = regs->regs[insn.i_format.rt];
__asm__(
#ifdef __BIG_ENDIAN
".set\tnoat\n"
"1:\tsb\t%0,1(%1)\n\t"
"srl\t$1,%0,0x8\n"
"2:\tsb\t$1,0(%1)\n\t"
".set\tat\n\t"
#endif
#ifdef __LITTLE_ENDIAN
".set\tnoat\n"
"1:\tsb\t%0,0(%1)\n\t"
"srl\t$1,%0,0x8\n"
"2:\tsb\t$1,1(%1)\n\t"
".set\tat\n\t"
#endif
".section\t__ex_table,\"a\"\n\t"
STR(PTR)"\t1b,%2\n\t"
STR(PTR)"\t2b,%2\n\t"
".previous"
: /* no outputs */
:"r" (value), "r" (addr), "i" (&&fault)
:"$1");
return;
case sw_op:
check_axs(pc, addr, 4);
value = regs->regs[insn.i_format.rt];
__asm__(
#ifdef __BIG_ENDIAN
"1:\tswl\t%0,(%1)\n"
"2:\tswr\t%0,3(%1)\n\t"
#endif
#ifdef __LITTLE_ENDIAN
"1:\tswl\t%0,3(%1)\n"
"2:\tswr\t%0,(%1)\n\t"
#endif
".section\t__ex_table,\"a\"\n\t"
STR(PTR)"\t1b,%2\n\t"
STR(PTR)"\t2b,%2\n\t"
".previous"
: /* no outputs */
:"r" (value), "r" (addr), "i" (&&fault));
return;
case sd_op:
check_axs(pc, addr, 8);
value = regs->regs[insn.i_format.rt];
__asm__(
".set\tmips3\n"
#ifdef __BIG_ENDIAN
"1:\tsdl\t%0,(%1)\n"
"2:\tsdr\t%0,7(%1)\n\t"
#endif
#ifdef __LITTLE_ENDIAN
"1:\tsdl\t%0,7(%1)\n"
"2:\tsdr\t%0,(%1)\n\t"
#endif
".set\tmips0\n\t"
".section\t__ex_table,\"a\"\n\t"
STR(PTR)"\t1b,%2\n\t"
STR(PTR)"\t2b,%2\n\t"
".previous"
: /* no outputs */
:"r" (value), "r" (addr), "i" (&&fault));
return;
case lwc1_op:
case ldc1_op:
case swc1_op:
case sdc1_op:
/*
* I herewith declare: this does not happen. So send SIGBUS.
*/
goto sigbus;
case lwc2_op:
case ldc2_op:
case swc2_op:
case sdc2_op:
/*
* These are the coprocessor 2 load/stores. The current
* implementations don't use cp2 and cp2 should always be
* disabled in c0_status. So send SIGILL.
* (No longer true: The Sony Praystation uses cp2 for
* 3D matrix operations. Dunno if that thingy has a MMU ...)
*/
default:
/*
* Pheeee... We encountered an yet unknown instruction or
* cache coherence problem. Die sucker, die ...
*/
goto sigill;
}
return;
fault:
/* Did we have an exception handler installed? */
fixup = search_exception_table(regs->cp0_epc);
if (fixup) {
long new_epc;
new_epc = fixup_exception(dpf_reg, fixup, regs->cp0_epc);
printk(KERN_DEBUG "%s: Forwarding exception at [<%lx>] (%lx)\n",
current->comm, regs->cp0_epc, new_epc);
regs->cp0_epc = new_epc;
return;
}
die_if_kernel ("Unhandled kernel unaligned access", regs);
send_sig(SIGSEGV, current, 1);
return;
sigbus:
die_if_kernel ("Unhandled kernel unaligned access", regs);
send_sig(SIGBUS, current, 1);
return;
sigill:
die_if_kernel ("Unhandled kernel unaligned access or invalid instruction", regs);
send_sig(SIGILL, current, 1);
return;
}
#ifdef CONFIG_PROC_FS
unsigned long unaligned_instructions;
#endif
asmlinkage void do_ade(struct pt_regs *regs)
{
unsigned long pc;
extern int do_dsemulret(struct pt_regs *);
/*
* Address errors may be deliberately induced
* by the FPU emulator to take retake control
* of the CPU after executing the instruction
* in the delay slot of an emulated branch.
*/
if ((unsigned long)regs->cp0_epc == current->thread.dsemul_aerpc) {
do_dsemulret(regs);
return;
}
/*
* Did we catch a fault trying to load an instruction?
* This also catches attempts to activate MIPS16 code on
* CPUs which don't support it.
*/
if (regs->cp0_badvaddr == regs->cp0_epc)
goto sigbus;
pc = regs->cp0_epc + ((regs->cp0_cause & CAUSEF_BD) ? 4 : 0);
if (compute_return_epc(regs))
return;
if ((current->thread.mflags & MF_FIXADE) == 0)
goto sigbus;
emulate_load_store_insn(regs, regs->cp0_badvaddr, pc);
#ifdef CONFIG_PROC_FS
unaligned_instructions++;
#endif
return;
sigbus:
die_if_kernel ("Kernel unaligned instruction access", regs);
force_sig(SIGBUS, current);
return;
}
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