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#include <linux/list.h>
#include <linux/jhash.h>
#include <linux/spinlock.h>
// When handling mmap()/munmap()/mprotect() syscall tracing to notice
// memory map changes, we need to cache syscall entry parameter values
// for processing at syscall exit.
// __stp_tf_map_lock protects the hash table.
// Documentation/spinlocks.txt suggest we can be a bit more clever
// if we guarantee that in interrupt context we only read, not write
// the datastructures. We should never change the hash table or the
// contents in interrupt context (which should only ever call
// stap_find_map_map_info for getting stored info). So we might
// want to look into that if this seems a bottleneck.
static DEFINE_RWLOCK(__stp_tf_map_lock);
#define __STP_TF_HASH_BITS 4
#define __STP_TF_TABLE_SIZE (1 << __STP_TF_HASH_BITS)
#ifndef TASK_FINDER_MAP_ENTRY_ITEMS
#define TASK_FINDER_MAP_ENTRY_ITEMS 100
#endif
struct __stp_tf_map_entry {
/* private: */
struct hlist_node hlist;
int usage;
/* public: */
pid_t pid;
long syscall_no;
unsigned long arg0;
unsigned long arg1;
unsigned long arg2;
};
static struct __stp_tf_map_entry
__stp_tf_map_free_list_items[TASK_FINDER_MAP_ENTRY_ITEMS];
static struct hlist_head __stp_tf_map_free_list[1];
static struct hlist_head __stp_tf_map_table[__STP_TF_TABLE_SIZE];
// __stp_tf_map_initialize(): Initialize the free list. Grabs the
// lock.
static void
__stp_tf_map_initialize(void)
{
int i;
struct hlist_head *head = &__stp_tf_map_free_list[0];
unsigned long flags;
write_lock_irqsave(&__stp_tf_map_lock, flags);
for (i = 0; i < TASK_FINDER_MAP_ENTRY_ITEMS; i++) {
hlist_add_head(&__stp_tf_map_free_list_items[i].hlist, head);
}
write_unlock_irqrestore(&__stp_tf_map_lock, flags);
}
// __stp_tf_map_get_free_entry(): Returns an entry from the free list
// or NULL. The __stp_tf_map_lock must be write locked before calling this
// function.
static struct __stp_tf_map_entry *
__stp_tf_map_get_free_entry(void)
{
struct hlist_head *head = &__stp_tf_map_free_list[0];
struct hlist_node *node;
struct __stp_tf_map_entry *entry = NULL;
if (hlist_empty(head))
return NULL;
hlist_for_each_entry(entry, node, head, hlist) {
break;
}
if (entry != NULL)
hlist_del(&entry->hlist);
return entry;
}
// __stp_tf_map_put_free_entry(): Puts an entry back on the free
// list. The __stp_tf_map_lock must be write locked before calling this
// function.
static void
__stp_tf_map_put_free_entry(struct __stp_tf_map_entry *entry)
{
struct hlist_head *head = &__stp_tf_map_free_list[0];
hlist_add_head(&entry->hlist, head);
}
// __stp_tf_map_hash(): Compute the map hash.
static inline u32
__stp_tf_map_hash(struct task_struct *tsk)
{
return (jhash_1word(tsk->pid, 0) & (__STP_TF_TABLE_SIZE - 1));
}
// Get map_entry if the map is present in the map hash table.
// Returns NULL if not present. Takes a read lock on __stp_tf_map_lock.
static struct __stp_tf_map_entry *
__stp_tf_get_map_entry(struct task_struct *tsk)
{
struct hlist_head *head;
struct hlist_node *node;
struct __stp_tf_map_entry *entry;
unsigned long flags;
read_lock_irqsave(&__stp_tf_map_lock, flags);
head = &__stp_tf_map_table[__stp_tf_map_hash(tsk)];
hlist_for_each_entry(entry, node, head, hlist) {
if (tsk->pid == entry->pid) {
read_unlock_irqrestore(&__stp_tf_map_lock, flags);
return entry;
}
}
read_unlock_irqrestore(&__stp_tf_map_lock, flags);
return NULL;
}
// Add the map info to the map hash table. Takes a write lock on
// __stp_tf_map_lock.
static int
__stp_tf_add_map(struct task_struct *tsk, long syscall_no, unsigned long arg0,
unsigned long arg1, unsigned long arg2)
{
struct hlist_head *head;
struct hlist_node *node;
struct __stp_tf_map_entry *entry;
unsigned long flags;
write_lock_irqsave(&__stp_tf_map_lock, flags);
head = &__stp_tf_map_table[__stp_tf_map_hash(tsk)];
hlist_for_each_entry(entry, node, head, hlist) {
// If we find an existing entry, just increment the
// usage count.
if (tsk->pid == entry->pid) {
entry->usage++;
write_unlock_irqrestore(&__stp_tf_map_lock, flags);
return 0;
}
}
// Get an element from the free list.
entry = __stp_tf_map_get_free_entry();
if (!entry) {
write_unlock_irqrestore(&__stp_tf_map_lock, flags);
return -ENOMEM;
}
entry->usage = 1;
entry->pid = tsk->pid;
entry->syscall_no = syscall_no;
entry->arg0 = arg0;
entry->arg1 = arg1;
entry->arg2 = arg2;
hlist_add_head(&entry->hlist, head);
write_unlock_irqrestore(&__stp_tf_map_lock, flags);
return 0;
}
// Remove the map entry from the map hash table. Takes a write lock on
// __stp_tf_map_lock.
static int
__stp_tf_remove_map_entry(struct __stp_tf_map_entry *entry)
{
struct hlist_head *head;
struct hlist_node *node;
int found = 0;
if (entry != NULL) {
unsigned long flags;
write_lock_irqsave(&__stp_tf_map_lock, flags);
// Decrement the usage count.
entry->usage--;
// If the entry is unused, put it back on the free
// list.
if (entry->usage == 0) {
hlist_del(&entry->hlist);
__stp_tf_map_put_free_entry(entry);
}
write_unlock_irqrestore(&__stp_tf_map_lock, flags);
}
return 0;
}
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