[PATCH v2 56/76] ARC: Unaligned access emulation
From: Vineet Gupta
Date: Fri Jan 18 2013 - 07:33:21 EST
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@xxxxxxxxxxx>
Signed-off-by: Vineet Gupta <vgupta@xxxxxxxxxxxx>
Cc: Tim Yao <tim.yao@xxxxxxxxxxx>
---
arch/arc/Kconfig | 11 ++
arch/arc/include/asm/Kbuild | 1 -
arch/arc/include/asm/ptrace.h | 3 +
arch/arc/include/asm/unaligned.h | 29 +++++
arch/arc/kernel/Makefile | 1 +
arch/arc/kernel/disasm.c | 2 +-
arch/arc/kernel/entry.S | 13 ++
arch/arc/kernel/traps.c | 26 ++++
arch/arc/kernel/unaligned.c | 245 ++++++++++++++++++++++++++++++++++++++
9 files changed, 329 insertions(+), 2 deletions(-)
create mode 100644 arch/arc/include/asm/unaligned.h
create mode 100644 arch/arc/kernel/unaligned.c
diff --git a/arch/arc/Kconfig b/arch/arc/Kconfig
index c34f3c3..d735de8 100644
--- a/arch/arc/Kconfig
+++ b/arch/arc/Kconfig
@@ -341,6 +341,17 @@ config ARC_CURR_IN_REG
This reserved Register R25 to point to Current Task in
kernel mode. This saves memory access for each such access
+
+config ARC_MISALIGN_ACCESS
+ bool "Emulate unaligned memory access (userspace only)"
+ default N
+ select SYSCTL_ARCH_UNALIGN_NO_WARN
+ select SYSCTL_ARCH_UNALIGN_ALLOW
+ help
+ This enables misaligned 16 & 32 bit memory access from user space.
+ Use ONLY-IF-ABS-NECESSARY as it will be very slow and also can hide
+ potential bugs in code
+
config ARC_STACK_NONEXEC
bool "Make stack non-executable"
default n
diff --git a/arch/arc/include/asm/Kbuild b/arch/arc/include/asm/Kbuild
index 78e982d..b24089c 100644
--- a/arch/arc/include/asm/Kbuild
+++ b/arch/arc/include/asm/Kbuild
@@ -52,7 +52,6 @@ generic-y += topology.h
generic-y += trace_clock.h
generic-y += types.h
generic-y += ucontext.h
-generic-y += unaligned.h
generic-y += user.h
generic-y += vga.h
generic-y += xor.h
diff --git a/arch/arc/include/asm/ptrace.h b/arch/arc/include/asm/ptrace.h
index e4e1ac6..fd68c4b 100644
--- a/arch/arc/include/asm/ptrace.h
+++ b/arch/arc/include/asm/ptrace.h
@@ -127,6 +127,9 @@ struct user_regs_struct {
sp; \
})
+/* return 1 if PC in delay slot */
+#define delay_mode(regs) ((regs->status32 & STATUS_DE_MASK) == STATUS_DE_MASK)
+
#define in_syscall(regs) (regs->orig_r8 & orig_r8_IS_SCALL)
#define in_brkpt_trap(regs) (regs->orig_r8 & orig_r8_IS_BRKPT)
diff --git a/arch/arc/include/asm/unaligned.h b/arch/arc/include/asm/unaligned.h
new file mode 100644
index 0000000..5dbe63f
--- /dev/null
+++ b/arch/arc/include/asm/unaligned.h
@@ -0,0 +1,29 @@
+/*
+ * Copyright (C) 2004, 2007-2010, 2011-2012 Synopsys, Inc. (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.
+ */
+
+#ifndef _ASM_ARC_UNALIGNED_H
+#define _ASM_ARC_UNALIGNED_H
+
+/* ARC700 can't handle unaligned Data accesses. */
+
+#include <asm-generic/unaligned.h>
+#include <asm/ptrace.h>
+
+#ifdef CONFIG_ARC_MISALIGN_ACCESS
+int misaligned_fixup(unsigned long address, struct pt_regs *regs,
+ unsigned long cause, struct callee_regs *cregs);
+#else
+static inline int
+misaligned_fixup(unsigned long address, struct pt_regs *regs,
+ unsigned long cause, struct callee_regs *cregs)
+{
+ return 0;
+}
+#endif
+
+#endif /* _ASM_ARC_UNALIGNED_H */
diff --git a/arch/arc/kernel/Makefile b/arch/arc/kernel/Makefile
index f11318f..eda40d7 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 51bad8f..2f39028 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 7e392d4..0ef234e 100644
--- a/arch/arc/kernel/entry.S
+++ b/arch/arc/kernel/entry.S
@@ -12,6 +12,9 @@
* needed before task_pt_regs was invented. This saves a branch per call
* and more importantly allows clean invocation of post-syscall ptrace hook
*
+ * 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.
@@ -392,7 +395,17 @@ 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 c6396b4..ec802c5 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 0000000..4cd8163
--- /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@xxxxxxxxxxx
+ *
+ */
+
+#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;
+}
--
1.7.4.1
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