patch-2.1.44 linux/arch/mips/kernel/unaligned.c

• Lines: 468
• Date: Thu Jun 26 12:33:37 1997
• Orig file: v2.1.43/linux/arch/mips/kernel/unaligned.c
• Orig date: Wed Dec 31 16:00:00 1969

diff -u --recursive --new-file v2.1.43/linux/arch/mips/kernel/unaligned.c linux/arch/mips/kernel/unaligned.c
@@ -0,0 +1,467 @@
+/*
+ * 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 by Ralf Baechle
+ *
+ * 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 decieded 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 parameter x is 0 for disabeling software emulation.  Set bit 0 for
+ * enabeling software emulation and bit 1 for enabeling printing debug
+ * messages into syslog to aid finding address errors in programs.
+ *
+ * The logging feature is an addition over RISC/os and IRIX where only the
+ * values 0 and 1 are acceptable values for x.  I'll probably remove this
+ * hack later on.
+ *
+ * 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");
+ * }
+ *
+ * Until I've written the code to handle branch delay slots it may happen
+ * that the kernel receives an ades/adel instruction from an insn in a
+ * branch delay slot but is unable to handle this case.  The kernel knows
+ * this fact and therefore will kill the process.  For most code you can
+ * fix this temporarily by compiling with flags -fno-delayed-branch -Wa,-O0.
+ *
+ * Coprozessor 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/smp_lock.h>
+
+#include <asm/branch.h>
+#include <asm/byteorder.h>
+#include <asm/inst.h>
+#include <asm/uaccess.h>
+
+#undef CONF_NO_UNALIGNED_KERNEL_ACCESS
+#undef CONF_LOG_UNALIGNED_ACCESSES
+
+#define STR(x)  __STR(x)
+#define __STR(x)  #x
+
+typedef unsigned long register_t;
+
+/*
+ * User code may only access USEG; kernel code may access the
+ * entire address space.
+ */
+#define check_axs(p,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;
+	register_t value;
+
+	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 interrest.
+	 */
+	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 coprozessor 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 ...
+		 */
+		force_sig(SIGILL, current);
+	}
+	return;
+
+fault:
+	send_sig(SIGSEGV, current, 1);
+	return;
+sigbus:
+	send_sig(SIGBUS, current, 1);
+	return;
+}
+
+unsigned long unaligned_instructions;
+
+static inline void
+fix_ade(struct pt_regs *regs, unsigned long pc)
+{
+	/*
+	 * Did we catch a fault trying to load an instruction?
+	 */
+	if (regs->cp0_badvaddr == pc) {
+		/*
+		 * Phee...  Either the code is severly messed up or the
+		 * process tried to activate some MIPS16 code.
+		 */
+		force_sig(SIGBUS, current);
+	}
+
+	/*
+	 * Ok, this wasn't a failed instruction load.  The CPU was capable of
+	 * reading the instruction and faulted after this.  So we don't need
+	 * to verify_area the address of the instrucion.  We still don't
+	 * know whether the address used was legal and therefore need to do
+	 * verify_area().  The CPU already did the checking for legal
+	 * instructions for us, so we don't need to do this.
+	 */
+	emulate_load_store_insn(regs, regs->cp0_badvaddr, pc);
+	unaligned_instructions++;
+}
+
+#define kernel_address(x) ((long)(x) < 0)
+
+asmlinkage void
+do_ade(struct pt_regs *regs)
+{
+	register_t pc = regs->cp0_epc;
+	register_t badvaddr __attribute__ ((unused)) = regs->cp0_badvaddr;
+	char *adels;
+
+	lock_kernel();
+	adels = (((regs->cp0_cause & CAUSEF_EXCCODE) >>
+                  CAUSEB_EXCCODE) == 4) ? "adel" : "ades";
+
+#ifdef CONF_NO_UNALIGNED_KERNEL_ACCESS
+	/*
+	 * In an ideal world there are no unaligned accesses by the kernel.
+	 * So be a bit noisy ...
+	 */
+	if (kernel_address(badvaddr) && !user_mode(regs)) {
+		show_regs(regs);
+#ifdef __mips64
+		panic("Caught %s exception in kernel mode accessing %016Lx.",
+                      adels, badvaddr);
+#else
+		panic("Caught %s exception in kernel mode accessing %08lx.",
+                      adels, badvaddr);
+#endif
+	}
+#endif /* CONF_NO_UNALIGNED_KERNEL_ACCESS */
+
+#ifdef CONF_LOG_UNALIGNED_ACCESSES
+	if (current->tss.mflags & MF_LOGADE) {
+		register_t logpc = pc;
+		if (regs->cp0_cause & CAUSEF_BD)
+			logpc += 4;
+#ifdef __mips64
+		printk(KERN_DEBUG
+		       "Caught %s in '%s' at 0x%016Lx accessing 0x%016Lx.\n",
+		       adels, current->comm, logpc, regs->cp0_badvaddr);
+#else
+		printk(KERN_DEBUG
+		       "Caught %s in '%s' at 0x%08lx accessing 0x%08lx.\n",
+		       adels, current->comm, logpc, regs->cp0_badvaddr);
+#endif
+	}
+#endif /* CONF_LOG_UNALIGNED_ACCESSES */
+
+	if (compute_return_epc(regs))
+		goto out;
+	if(current->tss.mflags & MF_FIXADE) {
+		pc += ((regs->cp0_cause & CAUSEF_BD) ? 4 : 0);
+		fix_ade(regs, pc);
+		goto out;
+	}
+
+#ifdef CONF_DEBUG_EXCEPTIONS
+	show_regs(regs);
+#endif
+
+	force_sig(SIGBUS, current);
+
+out:
+	unlock_kernel();
+	return;
+}