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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>
This commit is contained in:
Vineet Gupta 2013-01-23 16:30:36 +05:30
parent bf14e3b979
commit 2e651ea159
9 changed files with 329 additions and 2 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

11
arch/arc/Kconfig
View File

@ -336,6 +336,17 @@ 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

1
arch/arc/include/asm/Kbuild
View File

@ -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

3
arch/arc/include/asm/ptrace.h
View File

@ -97,6 +97,9 @@ struct callee_regs {
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->event & orig_r8_IS_SCALL)
#define in_brkpt_trap(regs) (regs->event & orig_r8_IS_BRKPT)

29
arch/arc/include/asm/unaligned.h Normal file
View File

@ -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 */

1
arch/arc/kernel/Makefile
View File

@ -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

2
arch/arc/kernel/disasm.c
View File

@ -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

13
arch/arc/kernel/entry.S
View File

@ -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

26
arch/arc/kernel/traps.c
View File

@ -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

245
arch/arc/kernel/unaligned.c Normal file
View File

@ -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;
}