ARC: Unaligned access emulation

ARC700 doesn't natively support unaligned access, but can be emulated
-Unaligned Access Exception
-Disassembly at the Fault address to find the exact insn (long/short)

Also per Arnd's comment, we runtime control it using 2 sysctl knobs:
* SYSCTL_ARCH_UNALIGN_ALLOW: Runtime enable/disble
* SYSCTL_ARCH_UNALIGN_NO_WARN: Warn on each emulation attempt

Originally contributed by Tim Yao <tim.yao@amlogic.com>

Signed-off-by: Vineet Gupta <vgupta@synopsys.com>
Cc: Tim Yao <tim.yao@amlogic.com>
Acked-by: Arnd Bergmann <arnd@arndb.de>

5 files changed, 286 insertions, 1 deletions

diff --git a/arch/arc/kernel/Makefile b/arch/arc/kernel/Makefile
index d331bd7047a1..507a33d4a255 100644
--- a/arch/arc/kernel/Makefile
+++ b/arch/arc/kernel/Makefile
@@ -16,6 +16,7 @@ obj-$(CONFIG_MODULES)			+= arcksyms.o module.o
 obj-$(CONFIG_SMP)                       += smp.o
 obj-$(CONFIG_ARC_DW2_UNWIND)            += unwind.o
 obj-$(CONFIG_KPROBES)                   += kprobes.o
+obj-$(CONFIG_ARC_MISALIGN_ACCESS)       += unaligned.o
 
 obj-$(CONFIG_ARC_FPU_SAVE_RESTORE)      += fpu.o
 CFLAGS_fpu.o   += -mdpfp
diff --git a/arch/arc/kernel/disasm.c b/arch/arc/kernel/disasm.c
index 51bad8ff373b..2f390289a792 100644
--- a/arch/arc/kernel/disasm.c
+++ b/arch/arc/kernel/disasm.c
@@ -15,7 +15,7 @@
 #include <asm/disasm.h>
 #include <asm/uaccess.h>
 
-#if defined(CONFIG_KGDB) || defined(CONFIG_MISALIGN_ACCESS) || \
+#if defined(CONFIG_KGDB) || defined(CONFIG_ARC_MISALIGN_ACCESS) || \
         defined(CONFIG_KPROBES)
 
 /* disasm_instr: Analyses instruction at addr, stores
diff --git a/arch/arc/kernel/entry.S b/arch/arc/kernel/entry.S
index 021cfa46a1dc..f8efade15368 100644
--- a/arch/arc/kernel/entry.S
+++ b/arch/arc/kernel/entry.S
@@ -7,6 +7,9 @@
  * it under the terms of the GNU General Public License version 2 as
  * published by the Free Software Foundation.
  *
+ * vineetg: May 2011
+ *  -Userspace unaligned access emulation
+ *
  * vineetg: Feb 2011 (ptrace low level code fixes)
  *  -traced syscall return code (r0) was not saved into pt_regs for restoring
  *   into user reg-file when traded task rets to user space.
@@ -387,7 +390,17 @@ ARC_ENTRY EV_TLBProtV
         mov r1, r4              ; faulting address
         mov r2, sp              ; pt_regs
 
+#ifdef  CONFIG_ARC_MISALIGN_ACCESS
+        SAVE_CALLEE_SAVED_USER
+        mov r3, sp              ; callee_regs
+#endif
+
         bl  do_misaligned_access
+
+#ifdef  CONFIG_ARC_MISALIGN_ACCESS
+        DISCARD_CALLEE_SAVED_USER
+#endif
+
         b   ret_from_exception
 
 ARC_EXIT EV_TLBProtV
diff --git a/arch/arc/kernel/traps.c b/arch/arc/kernel/traps.c
index c6396b48fcd2..ec802c52a1ca 100644
--- a/arch/arc/kernel/traps.c
+++ b/arch/arc/kernel/traps.c
@@ -7,6 +7,9 @@
  * it under the terms of the GNU General Public License version 2 as
  * published by the Free Software Foundation.
  *
+ * vineetg: May 2011
+ *  -user-space unaligned access emulation
+ *
  * Rahul Trivedi: Codito Technologies 2004
  */
 
@@ -16,6 +19,7 @@
 #include <asm/ptrace.h>
 #include <asm/setup.h>
 #include <asm/kprobes.h>
+#include <asm/unaligned.h>
 
 void __init trap_init(void)
 {
@@ -79,7 +83,29 @@ DO_ERROR_INFO(SIGILL, "Illegal Insn (or Seq)", insterror_is_error, ILL_ILLOPC)
 DO_ERROR_INFO(SIGBUS, "Invalid Mem Access", do_memory_error, BUS_ADRERR)
 DO_ERROR_INFO(SIGTRAP, "Breakpoint Set", trap_is_brkpt, TRAP_BRKPT)
 
+#ifdef CONFIG_ARC_MISALIGN_ACCESS
+/*
+ * Entry Point for Misaligned Data access Exception, for emulating in software
+ */
+int do_misaligned_access(unsigned long cause, unsigned long address,
+                         struct pt_regs *regs, struct callee_regs *cregs)
+{
+        if (misaligned_fixup(address, regs, cause, cregs) != 0) {
+                siginfo_t info;
+
+                info.si_signo = SIGBUS;
+                info.si_errno = 0;
+                info.si_code = BUS_ADRALN;
+                info.si_addr = (void __user *)address;
+                return handle_exception(cause, "Misaligned Access", regs,
+                                          &info);
+        }
+        return 0;
+}
+
+#else
 DO_ERROR_INFO(SIGSEGV, "Misaligned Access", do_misaligned_access, SEGV_ACCERR)
+#endif
 
 /*
  * Entry point for miscll errors such as Nested Exceptions
diff --git a/arch/arc/kernel/unaligned.c b/arch/arc/kernel/unaligned.c
new file mode 100644
index 000000000000..4cd81633febd
--- /dev/null
+++ b/arch/arc/kernel/unaligned.c
@@ -0,0 +1,245 @@
+/*
+ * Copyright (C) 2011-2012 Synopsys (www.synopsys.com)
+ *
+ * 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.
+ *
+ * vineetg : May 2011
+ *  -Adapted (from .26 to .35)
+ *  -original contribution by Tim.yao@amlogic.com
+ *
+ */
+
+#include <linux/types.h>
+#include <linux/ptrace.h>
+#include <linux/uaccess.h>
+#include <asm/disasm.h>
+
+#define __get8_unaligned_check(val, addr, err)          \
+        __asm__(                                        \
+        "1:     ldb.ab  %1, [%2, 1]\n"                  \
+        "2:\n"                                          \
+        "       .section .fixup,\"ax\"\n"               \
+        "       .align  4\n"                            \
+        "3:     mov     %0, 1\n"                        \
+        "       b       2b\n"                           \
+        "       .previous\n"                            \
+        "       .section __ex_table,\"a\"\n"            \
+        "       .align  4\n"                            \
+        "       .long   1b, 3b\n"                       \
+        "       .previous\n"                            \
+        : "=r" (err), "=&r" (val), "=r" (addr)          \
+        : "0" (err), "2" (addr))
+
+#define get16_unaligned_check(val, addr)                \
+        do {                                            \
+                unsigned int err = 0, v, a = addr;      \
+                __get8_unaligned_check(v, a, err);      \
+                val =  v ;                              \
+                __get8_unaligned_check(v, a, err);      \
+                val |= v << 8;                          \
+                if (err)                                \
+                        goto fault;                     \
+        } while (0)
+
+#define get32_unaligned_check(val, addr)                \
+        do {                                            \
+                unsigned int err = 0, v, a = addr;      \
+                __get8_unaligned_check(v, a, err);      \
+                val =  v << 0;                          \
+                __get8_unaligned_check(v, a, err);      \
+                val |= v << 8;                          \
+                __get8_unaligned_check(v, a, err);      \
+                val |= v << 16;                         \
+                __get8_unaligned_check(v, a, err);      \
+                val |= v << 24;                         \
+                if (err)                                \
+                        goto fault;                     \
+        } while (0)
+
+#define put16_unaligned_check(val, addr)                \
+        do {                                            \
+                unsigned int err = 0, v = val, a = addr;\
+                                                        \
+                __asm__(                                \
+                "1:     stb.ab  %1, [%2, 1]\n"          \
+                "       lsr %1, %1, 8\n"                \
+                "2:     stb     %1, [%2]\n"             \
+                "3:\n"                                  \
+                "       .section .fixup,\"ax\"\n"       \
+                "       .align  4\n"                    \
+                "4:     mov     %0, 1\n"                \
+                "       b       3b\n"                   \
+                "       .previous\n"                    \
+                "       .section __ex_table,\"a\"\n"    \
+                "       .align  4\n"                    \
+                "       .long   1b, 4b\n"               \
+                "       .long   2b, 4b\n"               \
+                "       .previous\n"                    \
+                : "=r" (err), "=&r" (v), "=&r" (a)      \
+                : "0" (err), "1" (v), "2" (a));         \
+                                                        \
+                if (err)                                \
+                        goto fault;                     \
+        } while (0)
+
+#define put32_unaligned_check(val, addr)                \
+        do {                                            \
+                unsigned int err = 0, v = val, a = addr;\
+                __asm__(                                \
+                                                        \
+                "1:     stb.ab  %1, [%2, 1]\n"          \
+                "       lsr %1, %1, 8\n"                \
+                "2:     stb.ab  %1, [%2, 1]\n"          \
+                "       lsr %1, %1, 8\n"                \
+                "3:     stb.ab  %1, [%2, 1]\n"          \
+                "       lsr %1, %1, 8\n"                \
+                "4:     stb     %1, [%2]\n"             \
+                "5:\n"                                  \
+                "       .section .fixup,\"ax\"\n"       \
+                "       .align  4\n"                    \
+                "6:     mov     %0, 1\n"                \
+                "       b       5b\n"                   \
+                "       .previous\n"                    \
+                "       .section __ex_table,\"a\"\n"    \
+                "       .align  4\n"                    \
+                "       .long   1b, 6b\n"               \
+                "       .long   2b, 6b\n"               \
+                "       .long   3b, 6b\n"               \
+                "       .long   4b, 6b\n"               \
+                "       .previous\n"                    \
+                : "=r" (err), "=&r" (v), "=&r" (a)      \
+                : "0" (err), "1" (v), "2" (a));         \
+                                                        \
+                if (err)                                \
+                        goto fault;                     \
+        } while (0)
+
+/* sysctl hooks */
+int unaligned_enabled __read_mostly = 1;        /* Enabled by default */
+int no_unaligned_warning __read_mostly = 1;     /* Only 1 warning by default */
+
+static void fixup_load(struct disasm_state *state, struct pt_regs *regs,
+                        struct callee_regs *cregs)
+{
+        int val;
+
+        /* register write back */
+        if ((state->aa == 1) || (state->aa == 2)) {
+                set_reg(state->wb_reg, state->src1 + state->src2, regs, cregs);
+
+                if (state->aa == 2)
+                        state->src2 = 0;
+        }
+
+        if (state->zz == 0) {
+                get32_unaligned_check(val, state->src1 + state->src2);
+        } else {
+                get16_unaligned_check(val, state->src1 + state->src2);
+
+                if (state->x)
+                        val = (val << 16) >> 16;
+        }
+
+        if (state->pref == 0)
+                set_reg(state->dest, val, regs, cregs);
+
+        return;
+
+fault:  state->fault = 1;
+}
+
+static void fixup_store(struct disasm_state *state, struct pt_regs *regs,
+                        struct callee_regs *cregs)
+{
+        /* register write back */
+        if ((state->aa == 1) || (state->aa == 2)) {
+                set_reg(state->wb_reg, state->src2 + state->src3, regs, cregs);
+
+                if (state->aa == 3)
+                        state->src3 = 0;
+        } else if (state->aa == 3) {
+                if (state->zz == 2) {
+                        set_reg(state->wb_reg, state->src2 + (state->src3 << 1),
+                                regs, cregs);
+                } else if (!state->zz) {
+                        set_reg(state->wb_reg, state->src2 + (state->src3 << 2),
+                                regs, cregs);
+                } else {
+                        goto fault;
+                }
+        }
+
+        /* write fix-up */
+        if (!state->zz)
+                put32_unaligned_check(state->src1, state->src2 + state->src3);
+        else
+                put16_unaligned_check(state->src1, state->src2 + state->src3);
+
+        return;
+
+fault:  state->fault = 1;
+}
+
+/*
+ * Handle an unaligned access
+ * Returns 0 if successfully handled, 1 if some error happened
+ */
+int misaligned_fixup(unsigned long address, struct pt_regs *regs,
+                     unsigned long cause, struct callee_regs *cregs)
+{
+        struct disasm_state state;
+        char buf[TASK_COMM_LEN];
+
+        /* handle user mode only and only if enabled by sysadmin */
+        if (!user_mode(regs) || !unaligned_enabled)
+                return 1;
+
+        if (no_unaligned_warning) {
+                pr_warn_once("%s(%d) made unaligned access which was emulated"
+                             " by kernel assist\n. This can degrade application"
+                             " performance significantly\n. To enable further"
+                             " logging of such instances, please \n"
+                             " echo 0 > /proc/sys/kernel/ignore-unaligned-usertrap\n",
+                             get_task_comm(buf, current), task_pid_nr(current));
+        } else {
+                /* Add rate limiting if it gets down to it */
+                pr_warn("%s(%d): unaligned access to/from 0x%lx by PC: 0x%lx\n",
+                        get_task_comm(buf, current), task_pid_nr(current),
+                        address, regs->ret);
+
+        }
+
+        disasm_instr(regs->ret, &state, 1, regs, cregs);
+
+        if (state.fault)
+                goto fault;
+
+        /* ldb/stb should not have unaligned exception */
+        if ((state.zz == 1) || (state.di))
+                goto fault;
+
+        if (!state.write)
+                fixup_load(&state, regs, cregs);
+        else
+                fixup_store(&state, regs, cregs);
+
+        if (state.fault)
+                goto fault;
+
+        if (delay_mode(regs)) {
+                regs->ret = regs->bta;
+                regs->status32 &= ~STATUS_DE_MASK;
+        } else {
+                regs->ret += state.instr_len;
+        }
+
+        return 0;
+
+fault:
+        pr_err("Alignment trap: fault in fix-up %08lx at [<%08lx>]\n",
+                state.words[0], address);
+
+        return 1;
+}