arch/i386/Kconfig.debug


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menu "Kernel hacking"

config TRACE_IRQFLAGS_SUPPORT
	bool
	default y

source "lib/Kconfig.debug"

config EARLY_PRINTK
	bool "Early printk" if EMBEDDED && DEBUG_KERNEL
	default y
	help
	  Write kernel log output directly into the VGA buffer or to a serial
	  port.

	  This is useful for kernel debugging when your machine crashes very
	  early before the console code is initialized. For normal operation
	  it is not recommended because it looks ugly and doesn't cooperate
	  with klogd/syslogd or the X server. You should normally N here,
	  unless you want to debug such a crash.

config DEBUG_STACKOVERFLOW
	bool "Check for stack overflows"
	depends on DEBUG_KERNEL
	help
	  This option will cause messages to be printed if free stack space
	  drops below a certain limit.

config DEBUG_STACK_USAGE
	bool "Stack utilization instrumentation"
	depends on DEBUG_KERNEL
	help
	  Enables the display of the minimum amount of free stack which each
	  task has ever had available in the sysrq-T and sysrq-P debug output.

	  This option will slow down process creation somewhat.

comment "Page alloc debug is incompatible with Software Suspend on i386"
	depends on DEBUG_KERNEL && SOFTWARE_SUSPEND

config DEBUG_PAGEALLOC
	bool "Debug page memory allocations"
	depends on DEBUG_KERNEL && !SOFTWARE_SUSPEND && !HUGETLBFS
	help
	  Unmap pages from the kernel linear mapping after free_pages().
	  This results in a large slowdown, but helps to find certain types
	  of memory corruptions.

config DEBUG_RODATA
	bool "Write protect kernel read-only data structures"
	depends on DEBUG_KERNEL
	help
	  Mark the kernel read-only data as write-protected in the pagetables,
	  in order to catch accidental (and incorrect) writes to such const
	  data. This option may have a slight performance impact because a
	  portion of the kernel code won't be covered by a 2MB TLB anymore.
	  If in doubt, say "N".

config 4KSTACKS
	bool "Use 4Kb for kernel stacks instead of 8Kb"
	depends on DEBUG_KERNEL
	help
	  If you say Y here the kernel will use a 4Kb stacksize for the
	  kernel stack attached to each process/thread. This facilitates
	  running more threads on a system and also reduces the pressure
	  on the VM subsystem for higher order allocations. This option
	  will also use IRQ stacks to compensate for the reduced stackspace.

config X86_FIND_SMP_CONFIG
	bool
	depends on X86_LOCAL_APIC || X86_VOYAGER
	default y

config X86_MPPARSE
	bool
	depends on X86_LOCAL_APIC && !X86_VISWS
	default y

config DOUBLEFAULT
	default y
	bool "Enable doublefault exception handler" if EMBEDDED
	help
          This option allows trapping of rare doublefault exceptions that
          would otherwise cause a system to silently reboot. Disabling this
          option saves about 4k and might cause you much additional grey
          hair.

config DEBUG_PARAVIRT
	bool "Enable some paravirtualization debugging"
	default n
	depends on PARAVIRT && DEBUG_KERNEL
	help
	  Currently deliberately clobbers regs which are allowed to be
	  clobbered in inlined paravirt hooks, even in native mode.
	  If turning this off solves a problem, then DISABLE_INTERRUPTS() or
	  ENABLE_INTERRUPTS() is lying about what registers can be clobbered.

endmenu
/*
 * dcookies.c
 *
 * Copyright 2002 John Levon <levon@movementarian.org>
 *
 * Persistent cookie-path mappings. These are used by
 * profilers to convert a per-task EIP value into something
 * non-transitory that can be processed at a later date.
 * This is done by locking the dentry/vfsmnt pair in the
 * kernel until released by the tasks needing the persistent
 * objects. The tag is simply an unsigned long that refers
 * to the pair and can be looked up from userspace.
 */

#include <linux/syscalls.h>
#include <linux/module.h>
#include <linux/slab.h>
#include <linux/list.h>
#include <linux/mount.h>
#include <linux/capability.h>
#include <linux/dcache.h>
#include <linux/mm.h>
#include <linux/err.h>
#include <linux/errno.h>
#include <linux/dcookies.h>
#include <linux/mutex.h>
#include <linux/path.h>
#include <asm/uaccess.h>

/* The dcookies are allocated from a kmem_cache and
 * hashed onto a small number of lists. None of the
 * code here is particularly performance critical
 */
struct dcookie_struct {
	struct path path;
	struct list_head hash_list;
};

static LIST_HEAD(dcookie_users);
static DEFINE_MUTEX(dcookie_mutex);
static struct kmem_cache *dcookie_cache __read_mostly;
static struct list_head *dcookie_hashtable __read_mostly;
static size_t hash_size __read_mostly;

static inline int is_live(void)
{
	return !(list_empty(&dcookie_users));
}


/* The dentry is locked, its address will do for the cookie */
static inline unsigned long dcookie_value(struct dcookie_struct * dcs)
{
	return (unsigned long)dcs->path.dentry;
}


static size_t dcookie_hash(unsigned long dcookie)
{
	return (dcookie >> L1_CACHE_SHIFT) & (hash_size - 1);
}


static struct dcookie_struct * find_dcookie(unsigned long dcookie)
{
	struct dcookie_struct *found = NULL;
	struct dcookie_struct * dcs;
	struct list_head * pos;
	struct list_head * list;

	list = dcookie_hashtable + dcookie_hash(dcookie);

	list_for_each(pos, list) {
		dcs = list_entry(pos, struct dcookie_struct, hash_list);
		if (dcookie_value(dcs) == dcookie) {
			found = dcs;
			break;
		}
	}

	return found;
}


static void hash_dcookie(struct dcookie_struct * dcs)
{
	struct list_head * list = dcookie_hashtable + dcookie_hash(dcookie_value(dcs));
	list_add(&dcs->hash_list, list);
}


static struct dcookie_struct *alloc_dcookie(struct path *path)
{
	struct dcookie_struct *dcs = kmem_cache_alloc(dcookie_cache,
							GFP_KERNEL);
	struct dentry *d;
	if (!dcs)
		return NULL;

	d = path->dentry;
	spin_lock(&d->d_lock);
	d->d_flags |= DCACHE_COOKIE;
	spin_unlock(&d->d_lock);

	dcs->path = *path;
	path_get(path);
	hash_dcookie(dcs);
	return dcs;
}


/* This is the main kernel-side routine that retrieves the cookie
 * value for a dentry/vfsmnt pair.
 */
int get_dcookie(struct path *path, unsigned long *cookie)
{
	int err = 0;
	struct dcookie_struct * dcs;

	mutex_lock(&dcookie_mutex);

	if (!is_live()) {
		err = -EINVAL;
		goto out;
	}

	if (path->dentry->d_flags & DCACHE_COOKIE) {
		dcs = find_dcookie((unsigned long)path->dentry);
	} else {
		dcs = alloc_dcookie(path);
		if (!dcs) {
			err = -ENOMEM;
			goto out;
		}
	}

	*cookie = dcookie_value(dcs);

out:
	mutex_unlock(&dcookie_mutex);
	return err;
}


/* And here is where the userspace process can look up the cookie value
 * to retrieve the path.
 */
SYSCALL_DEFINE(lookup_dcookie)(u64 cookie64, char __user * buf, size_t len)
{
	unsigned long cookie = (unsigned long)cookie64;
	int err = -EINVAL;
	char * kbuf;
	char * path;
	size_t pathlen;
	struct dcookie_struct * dcs;

	/* we could leak path information to users
	 * without dir read permission without this
	 */
	if (!capable(CAP_SYS_ADMIN))
		return -EPERM;

	mutex_lock(&dcookie_mutex);

	if (!is_live()) {
		err = -EINVAL;
		goto out;
	}

	if (!(dcs = find_dcookie(cookie)))
		goto out;

	err = -ENOMEM;
	kbuf = kmalloc(PAGE_SIZE, GFP_KERNEL);
	if (!kbuf)
		goto out;

	/* FIXME: (deleted) ? */
	path = d_path(&dcs->path, kbuf, PAGE_SIZE);

	if (IS_ERR(path)) {
		err = PTR_ERR(path);
		goto out_free;
	}

	err = -ERANGE;
 
	pathlen = kbuf + PAGE_SIZE - path;
	if (pathlen <= len) {
		err = pathlen;
		if (copy_to_user(buf, path, pathlen))
			err = -EFAULT;
	}

out_free:
	kfree(kbuf);
out:
	mutex_unlock(&dcookie_mutex);
	return err;
}
#ifdef CONFIG_HAVE_SYSCALL_WRAPPERS
asmlinkage long SyS_lookup_dcookie(u64 cookie64, long buf, long len)
{
	return SYSC_lookup_dcookie(cookie64, (char __user *) buf, (size_t) len);
}
SYSCALL_ALIAS(sys_lookup_dcookie, SyS_lookup_dcookie);
#endif

static int dcookie_init(void)
{
	struct list_head * d;
	unsigned int i, hash_bits;
	int err = -ENOMEM;

	dcookie_cache = kmem_cache_create("dcookie_cache",
		sizeof(struct dcookie_struct),
		0, 0, NULL);

	if (!dcookie_cache)
		goto out;

	dcookie_hashtable = kmalloc(PAGE_SIZE, GFP_KERNEL);
	if (!dcookie_hashtable)
		goto out_kmem;

	err = 0;

	/*
	 * Find the power-of-two list-heads that can fit into the allocation..
	 * We don't guarantee that "sizeof(struct list_head)" is necessarily
	 * a power-of-two.
	 */
	hash_size = PAGE_SIZE / sizeof(struct list_head);
	hash_bits = 0;
	do {
		hash_bits++;
	} while ((hash_size >> hash_bits) != 0);
	hash_bits--;

	/*
	 * Re-calculate the actual number of entries and the mask
	 * from the number of bits we can fit.
	 */
	hash_size = 1UL << hash_bits;

	/* And initialize the newly allocated array */
	d = dcookie_hashtable;
	i = hash_size;
	do {
		INIT_LIST_HEAD(d);
		d++;
		i--;
	} while (i);

out:
	return err;
out_kmem:
	kmem_cache_destroy(dcookie_cache);
	goto out;
}


static void free_dcookie(struct dcookie_struct * dcs)
{
	struct dentry *d = dcs->path.dentry;

	spin_lock(&d->d_lock);
	d->d_flags &= ~DCACHE_COOKIE;
	spin_unlock(&d->d_lock);

	path_put(&dcs->path);
	kmem_cache_free(dcookie_cache, dcs);
}


static void dcookie_exit(void)
{
	struct list_head * list;
	struct list_head * pos;
	struct list_head * pos2;
	struct dcookie_struct * dcs;
	size_t i;

	for (i = 0; i < hash_size; ++i) {
		list = dcookie_hashtable + i;
		list_for_each_safe(pos, pos2, list) {
			dcs = list_entry(pos, struct dcookie_struct, hash_list);
			list_del(&dcs->hash_list);
			free_dcookie(dcs);
		}
	}

	kfree(dcookie_hashtable);
	kmem_cache_destroy(dcookie_cache);
}


struct dcookie_user {
	struct list_head next;
};
 
struct dcookie_user * dcookie_register(void)
{
	struct dcookie_user * user;

	mutex_lock(&dcookie_mutex);

	user = kmalloc(sizeof(struct dcookie_user), GFP_KERNEL);
	if (!user)
		goto out;

	if (!is_live() && dcookie_init())
		goto out_free;

	list_add(&user->next, &dcookie_users);

out:
	mutex_unlock(&dcookie_mutex);
	return user;
out_free:
	kfree(user);
	user = NULL;
	goto out;
}


void dcookie_unregister(struct dcookie_user * user)
{
	mutex_lock(&dcookie_mutex);

	list_del(&user->next);
	kfree(user);

	if (!is_live())
		dcookie_exit();

	mutex_unlock(&dcookie_mutex);
}

EXPORT_SYMBOL_GPL(dcookie_register);
EXPORT_SYMBOL_GPL(dcookie_unregister);
EXPORT_SYMBOL_GPL(get_dcookie);