[RFC][PATCH] ARM: ptrace: remove single-step emulation code
Will Deacon
will.deacon at arm.com
Wed Jan 19 10:07:15 EST 2011
PTRACE_SINGLESTEP is a ptrace request designed to offer single-stepping
support to userspace when the underlying architecture has hardware
support for this operation.
On ARM, we set arch_has_single_step() to 1 and attempt to emulate hardware
single-stepping by disassembling the current instruction to determine the
next pc and placing a software breakpoint on that location.
Unfortunately this has the following problems:
1.) Only a subset of ARMv7 instructions are supported
2.) Thumb-2 is unsupported
3.) The code is not SMP safe
We could try to fix this code, but it turns out that nobody uses it anyway.
GDB, for example, uses PTRACE_POKETEXT and PTRACE_PEEKTEXT to manage
breakpoints itself and does not require any kernel assistance.
This patch removes the single-step emulation code from ptrace meaning that
the PTRACE_SINGLESTEP request will return -EIO on ARM.
Signed-off-by: Will Deacon <will.deacon at arm.com>
---
I'm posting this as an RFC to see if anybody has a good reason to keep this
code around. There's also a chance I've missed an opportunity to remove some
related code, but I think I found everything. Tested on a Versatile Express,
single-stepping in GDB worked fine.
arch/arm/include/asm/processor.h | 12 --
arch/arm/include/asm/ptrace.h | 2 -
arch/arm/include/asm/traps.h | 1 +
arch/arm/kernel/ptrace.c | 383 +-------------------------------------
arch/arm/kernel/ptrace.h | 37 ----
arch/arm/kernel/signal.c | 9 -
arch/arm/kernel/traps.c | 1 -
7 files changed, 2 insertions(+), 443 deletions(-)
delete mode 100644 arch/arm/kernel/ptrace.h
diff --git a/arch/arm/include/asm/processor.h b/arch/arm/include/asm/processor.h
index 67357ba..b439b41 100644
--- a/arch/arm/include/asm/processor.h
+++ b/arch/arm/include/asm/processor.h
@@ -29,19 +29,7 @@
#define STACK_TOP_MAX TASK_SIZE
#endif
-union debug_insn {
- u32 arm;
- u16 thumb;
-};
-
-struct debug_entry {
- u32 address;
- union debug_insn insn;
-};
-
struct debug_info {
- int nsaved;
- struct debug_entry bp[2];
#ifdef CONFIG_HAVE_HW_BREAKPOINT
struct perf_event *hbp[ARM_MAX_HBP_SLOTS];
#endif
diff --git a/arch/arm/include/asm/ptrace.h b/arch/arm/include/asm/ptrace.h
index 783d50f..a8ff22b 100644
--- a/arch/arm/include/asm/ptrace.h
+++ b/arch/arm/include/asm/ptrace.h
@@ -130,8 +130,6 @@ struct pt_regs {
#ifdef __KERNEL__
-#define arch_has_single_step() (1)
-
#define user_mode(regs) \
(((regs)->ARM_cpsr & 0xf) == 0)
diff --git a/arch/arm/include/asm/traps.h b/arch/arm/include/asm/traps.h
index 1b960d5..f90756d 100644
--- a/arch/arm/include/asm/traps.h
+++ b/arch/arm/include/asm/traps.h
@@ -45,6 +45,7 @@ static inline int in_exception_text(unsigned long ptr)
extern void __init early_trap_init(void);
extern void dump_backtrace_entry(unsigned long where, unsigned long from, unsigned long frame);
+extern void ptrace_break(struct task_struct *tsk, struct pt_regs *regs);
extern void *vectors_page;
diff --git a/arch/arm/kernel/ptrace.c b/arch/arm/kernel/ptrace.c
index 19c6816..eace844 100644
--- a/arch/arm/kernel/ptrace.c
+++ b/arch/arm/kernel/ptrace.c
@@ -26,8 +26,6 @@
#include <asm/system.h>
#include <asm/traps.h>
-#include "ptrace.h"
-
#define REG_PC 15
#define REG_PSR 16
/*
@@ -184,389 +182,12 @@ put_user_reg(struct task_struct *task, int offset, long data)
return ret;
}
-static inline int
-read_u32(struct task_struct *task, unsigned long addr, u32 *res)
-{
- int ret;
-
- ret = access_process_vm(task, addr, res, sizeof(*res), 0);
-
- return ret == sizeof(*res) ? 0 : -EIO;
-}
-
-static inline int
-read_instr(struct task_struct *task, unsigned long addr, u32 *res)
-{
- int ret;
-
- if (addr & 1) {
- u16 val;
- ret = access_process_vm(task, addr & ~1, &val, sizeof(val), 0);
- ret = ret == sizeof(val) ? 0 : -EIO;
- *res = val;
- } else {
- u32 val;
- ret = access_process_vm(task, addr & ~3, &val, sizeof(val), 0);
- ret = ret == sizeof(val) ? 0 : -EIO;
- *res = val;
- }
- return ret;
-}
-
-/*
- * Get value of register `rn' (in the instruction)
- */
-static unsigned long
-ptrace_getrn(struct task_struct *child, unsigned long insn)
-{
- unsigned int reg = (insn >> 16) & 15;
- unsigned long val;
-
- val = get_user_reg(child, reg);
- if (reg == 15)
- val += 8;
-
- return val;
-}
-
-/*
- * Get value of operand 2 (in an ALU instruction)
- */
-static unsigned long
-ptrace_getaluop2(struct task_struct *child, unsigned long insn)
-{
- unsigned long val;
- int shift;
- int type;
-
- if (insn & 1 << 25) {
- val = insn & 255;
- shift = (insn >> 8) & 15;
- type = 3;
- } else {
- val = get_user_reg (child, insn & 15);
-
- if (insn & (1 << 4))
- shift = (int)get_user_reg (child, (insn >> 8) & 15);
- else
- shift = (insn >> 7) & 31;
-
- type = (insn >> 5) & 3;
- }
-
- switch (type) {
- case 0: val <<= shift; break;
- case 1: val >>= shift; break;
- case 2:
- val = (((signed long)val) >> shift);
- break;
- case 3:
- val = (val >> shift) | (val << (32 - shift));
- break;
- }
- return val;
-}
-
-/*
- * Get value of operand 2 (in a LDR instruction)
- */
-static unsigned long
-ptrace_getldrop2(struct task_struct *child, unsigned long insn)
-{
- unsigned long val;
- int shift;
- int type;
-
- val = get_user_reg(child, insn & 15);
- shift = (insn >> 7) & 31;
- type = (insn >> 5) & 3;
-
- switch (type) {
- case 0: val <<= shift; break;
- case 1: val >>= shift; break;
- case 2:
- val = (((signed long)val) >> shift);
- break;
- case 3:
- val = (val >> shift) | (val << (32 - shift));
- break;
- }
- return val;
-}
-
-#define OP_MASK 0x01e00000
-#define OP_AND 0x00000000
-#define OP_EOR 0x00200000
-#define OP_SUB 0x00400000
-#define OP_RSB 0x00600000
-#define OP_ADD 0x00800000
-#define OP_ADC 0x00a00000
-#define OP_SBC 0x00c00000
-#define OP_RSC 0x00e00000
-#define OP_ORR 0x01800000
-#define OP_MOV 0x01a00000
-#define OP_BIC 0x01c00000
-#define OP_MVN 0x01e00000
-
-static unsigned long
-get_branch_address(struct task_struct *child, unsigned long pc, unsigned long insn)
-{
- u32 alt = 0;
-
- switch (insn & 0x0e000000) {
- case 0x00000000:
- case 0x02000000: {
- /*
- * data processing
- */
- long aluop1, aluop2, ccbit;
-
- if ((insn & 0x0fffffd0) == 0x012fff10) {
- /*
- * bx or blx
- */
- alt = get_user_reg(child, insn & 15);
- break;
- }
-
-
- if ((insn & 0xf000) != 0xf000)
- break;
-
- aluop1 = ptrace_getrn(child, insn);
- aluop2 = ptrace_getaluop2(child, insn);
- ccbit = get_user_reg(child, REG_PSR) & PSR_C_BIT ? 1 : 0;
-
- switch (insn & OP_MASK) {
- case OP_AND: alt = aluop1 & aluop2; break;
- case OP_EOR: alt = aluop1 ^ aluop2; break;
- case OP_SUB: alt = aluop1 - aluop2; break;
- case OP_RSB: alt = aluop2 - aluop1; break;
- case OP_ADD: alt = aluop1 + aluop2; break;
- case OP_ADC: alt = aluop1 + aluop2 + ccbit; break;
- case OP_SBC: alt = aluop1 - aluop2 + ccbit; break;
- case OP_RSC: alt = aluop2 - aluop1 + ccbit; break;
- case OP_ORR: alt = aluop1 | aluop2; break;
- case OP_MOV: alt = aluop2; break;
- case OP_BIC: alt = aluop1 & ~aluop2; break;
- case OP_MVN: alt = ~aluop2; break;
- }
- break;
- }
-
- case 0x04000000:
- case 0x06000000:
- /*
- * ldr
- */
- if ((insn & 0x0010f000) == 0x0010f000) {
- unsigned long base;
-
- base = ptrace_getrn(child, insn);
- if (insn & 1 << 24) {
- long aluop2;
-
- if (insn & 0x02000000)
- aluop2 = ptrace_getldrop2(child, insn);
- else
- aluop2 = insn & 0xfff;
-
- if (insn & 1 << 23)
- base += aluop2;
- else
- base -= aluop2;
- }
- read_u32(child, base, &alt);
- }
- break;
-
- case 0x08000000:
- /*
- * ldm
- */
- if ((insn & 0x00108000) == 0x00108000) {
- unsigned long base;
- unsigned int nr_regs;
-
- if (insn & (1 << 23)) {
- nr_regs = hweight16(insn & 65535) << 2;
-
- if (!(insn & (1 << 24)))
- nr_regs -= 4;
- } else {
- if (insn & (1 << 24))
- nr_regs = -4;
- else
- nr_regs = 0;
- }
-
- base = ptrace_getrn(child, insn);
-
- read_u32(child, base + nr_regs, &alt);
- break;
- }
- break;
-
- case 0x0a000000: {
- /*
- * bl or b
- */
- signed long displ;
- /* It's a branch/branch link: instead of trying to
- * figure out whether the branch will be taken or not,
- * we'll put a breakpoint at both locations. This is
- * simpler, more reliable, and probably not a whole lot
- * slower than the alternative approach of emulating the
- * branch.
- */
- displ = (insn & 0x00ffffff) << 8;
- displ = (displ >> 6) + 8;
- if (displ != 0 && displ != 4)
- alt = pc + displ;
- }
- break;
- }
-
- return alt;
-}
-
-static int
-swap_insn(struct task_struct *task, unsigned long addr,
- void *old_insn, void *new_insn, int size)
-{
- int ret;
-
- ret = access_process_vm(task, addr, old_insn, size, 0);
- if (ret == size)
- ret = access_process_vm(task, addr, new_insn, size, 1);
- return ret;
-}
-
-static void
-add_breakpoint(struct task_struct *task, struct debug_info *dbg, unsigned long addr)
-{
- int nr = dbg->nsaved;
-
- if (nr < 2) {
- u32 new_insn = BREAKINST_ARM;
- int res;
-
- res = swap_insn(task, addr, &dbg->bp[nr].insn, &new_insn, 4);
-
- if (res == 4) {
- dbg->bp[nr].address = addr;
- dbg->nsaved += 1;
- }
- } else
- printk(KERN_ERR "ptrace: too many breakpoints\n");
-}
-
-/*
- * Clear one breakpoint in the user program. We copy what the hardware
- * does and use bit 0 of the address to indicate whether this is a Thumb
- * breakpoint or an ARM breakpoint.
- */
-static void clear_breakpoint(struct task_struct *task, struct debug_entry *bp)
-{
- unsigned long addr = bp->address;
- union debug_insn old_insn;
- int ret;
-
- if (addr & 1) {
- ret = swap_insn(task, addr & ~1, &old_insn.thumb,
- &bp->insn.thumb, 2);
-
- if (ret != 2 || old_insn.thumb != BREAKINST_THUMB)
- printk(KERN_ERR "%s:%d: corrupted Thumb breakpoint at "
- "0x%08lx (0x%04x)\n", task->comm,
- task_pid_nr(task), addr, old_insn.thumb);
- } else {
- ret = swap_insn(task, addr & ~3, &old_insn.arm,
- &bp->insn.arm, 4);
-
- if (ret != 4 || old_insn.arm != BREAKINST_ARM)
- printk(KERN_ERR "%s:%d: corrupted ARM breakpoint at "
- "0x%08lx (0x%08x)\n", task->comm,
- task_pid_nr(task), addr, old_insn.arm);
- }
-}
-
-void ptrace_set_bpt(struct task_struct *child)
-{
- struct pt_regs *regs;
- unsigned long pc;
- u32 insn;
- int res;
-
- regs = task_pt_regs(child);
- pc = instruction_pointer(regs);
-
- if (thumb_mode(regs)) {
- printk(KERN_WARNING "ptrace: can't handle thumb mode\n");
- return;
- }
-
- res = read_instr(child, pc, &insn);
- if (!res) {
- struct debug_info *dbg = &child->thread.debug;
- unsigned long alt;
-
- dbg->nsaved = 0;
-
- alt = get_branch_address(child, pc, insn);
- if (alt)
- add_breakpoint(child, dbg, alt);
-
- /*
- * Note that we ignore the result of setting the above
- * breakpoint since it may fail. When it does, this is
- * not so much an error, but a forewarning that we may
- * be receiving a prefetch abort shortly.
- *
- * If we don't set this breakpoint here, then we can
- * lose control of the thread during single stepping.
- */
- if (!alt || predicate(insn) != PREDICATE_ALWAYS)
- add_breakpoint(child, dbg, pc + 4);
- }
-}
-
-/*
- * Ensure no single-step breakpoint is pending. Returns non-zero
- * value if child was being single-stepped.
- */
-void ptrace_cancel_bpt(struct task_struct *child)
-{
- int i, nsaved = child->thread.debug.nsaved;
-
- child->thread.debug.nsaved = 0;
-
- if (nsaved > 2) {
- printk("ptrace_cancel_bpt: bogus nsaved: %d!\n", nsaved);
- nsaved = 2;
- }
-
- for (i = 0; i < nsaved; i++)
- clear_breakpoint(child, &child->thread.debug.bp[i]);
-}
-
-void user_disable_single_step(struct task_struct *task)
-{
- task->ptrace &= ~PT_SINGLESTEP;
- ptrace_cancel_bpt(task);
-}
-
-void user_enable_single_step(struct task_struct *task)
-{
- task->ptrace |= PT_SINGLESTEP;
-}
-
/*
* Called by kernel/ptrace.c when detaching..
*/
void ptrace_disable(struct task_struct *child)
{
- user_disable_single_step(child);
+ /* Nothing to do. */
}
/*
@@ -576,8 +197,6 @@ void ptrace_break(struct task_struct *tsk, struct pt_regs *regs)
{
siginfo_t info;
- ptrace_cancel_bpt(tsk);
-
info.si_signo = SIGTRAP;
info.si_errno = 0;
info.si_code = TRAP_BRKPT;
diff --git a/arch/arm/kernel/ptrace.h b/arch/arm/kernel/ptrace.h
deleted file mode 100644
index 3926605..0000000
--- a/arch/arm/kernel/ptrace.h
+++ /dev/null
@@ -1,37 +0,0 @@
-/*
- * linux/arch/arm/kernel/ptrace.h
- *
- * Copyright (C) 2000-2003 Russell King
- *
- * 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.
- */
-#include <linux/ptrace.h>
-
-extern void ptrace_cancel_bpt(struct task_struct *);
-extern void ptrace_set_bpt(struct task_struct *);
-extern void ptrace_break(struct task_struct *, struct pt_regs *);
-
-/*
- * Send SIGTRAP if we're single-stepping
- */
-static inline void single_step_trap(struct task_struct *task)
-{
- if (task->ptrace & PT_SINGLESTEP) {
- ptrace_cancel_bpt(task);
- send_sig(SIGTRAP, task, 1);
- }
-}
-
-static inline void single_step_clear(struct task_struct *task)
-{
- if (task->ptrace & PT_SINGLESTEP)
- ptrace_cancel_bpt(task);
-}
-
-static inline void single_step_set(struct task_struct *task)
-{
- if (task->ptrace & PT_SINGLESTEP)
- ptrace_set_bpt(task);
-}
diff --git a/arch/arm/kernel/signal.c b/arch/arm/kernel/signal.c
index 907d5a6..7709668 100644
--- a/arch/arm/kernel/signal.c
+++ b/arch/arm/kernel/signal.c
@@ -20,7 +20,6 @@
#include <asm/unistd.h>
#include <asm/vfp.h>
-#include "ptrace.h"
#include "signal.h"
#define _BLOCKABLE (~(sigmask(SIGKILL) | sigmask(SIGSTOP)))
@@ -348,8 +347,6 @@ asmlinkage int sys_sigreturn(struct pt_regs *regs)
if (restore_sigframe(regs, frame))
goto badframe;
- single_step_trap(current);
-
return regs->ARM_r0;
badframe:
@@ -383,8 +380,6 @@ asmlinkage int sys_rt_sigreturn(struct pt_regs *regs)
if (do_sigaltstack(&frame->sig.uc.uc_stack, NULL, regs->ARM_sp) == -EFAULT)
goto badframe;
- single_step_trap(current);
-
return regs->ARM_r0;
badframe:
@@ -704,8 +699,6 @@ static void do_signal(struct pt_regs *regs, int syscall)
if (try_to_freeze())
goto no_signal;
- single_step_clear(current);
-
signr = get_signal_to_deliver(&info, &ka, regs, NULL);
if (signr > 0) {
sigset_t *oldset;
@@ -724,7 +717,6 @@ static void do_signal(struct pt_regs *regs, int syscall)
if (test_thread_flag(TIF_RESTORE_SIGMASK))
clear_thread_flag(TIF_RESTORE_SIGMASK);
}
- single_step_set(current);
return;
}
@@ -770,7 +762,6 @@ static void do_signal(struct pt_regs *regs, int syscall)
sigprocmask(SIG_SETMASK, ¤t->saved_sigmask, NULL);
}
}
- single_step_set(current);
}
asmlinkage void
diff --git a/arch/arm/kernel/traps.c b/arch/arm/kernel/traps.c
index ee57640..1f3f0e8 100644
--- a/arch/arm/kernel/traps.c
+++ b/arch/arm/kernel/traps.c
@@ -32,7 +32,6 @@
#include <asm/unwind.h>
#include <asm/tls.h>
-#include "ptrace.h"
#include "signal.h"
static const char *handler[]= { "prefetch abort", "data abort", "address exception", "interrupt" };
--
1.7.0.4
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