批判我的非侵入式堆调试器 [英] Critique my non-intrusive heap debugger
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问题描述
这是对昨天批评我的堆调试器的跟进。
堆调试器现在检测到以下类型的错误：
The heap debugger now detects the following kinds of errors:
- 内存泄漏（现在具有更详细的调试输出）
- 非法指针传递给删除删除）
- 错误的删除形式（数组与非数组）
- 缓冲区溢出
- 下溢
- memory leaks (now with more verbose debugging output)
- illegal pointers passed to delete (that also takes care of double deletes)
- wrong form of delete (array vs. non-array)
- buffer overflows
- buffer underflows
提前自由讨论并感谢！
#include <cstdio>
#include <cstdlib>
#include <cstring>
#include <new>
namespace
{
// I don't want to #include <algorithm> for a single function template :)
template <typename T>
void my_swap(T& x, T& y)
{
T z(x);
x = y;
y = z;
}
typedef unsigned char byte;
const byte CANARY[] = {0x5A, 0xFE, 0x6A, 0x8D,
0x5A, 0xFE, 0x6A, 0x8D,
0x5A, 0xFE, 0x6A, 0x8D,
0x5A, 0xFE, 0x6A, 0x8D};
bool canary_dead(const byte* cage)
{
bool dead = memcmp(cage, CANARY, sizeof CANARY);
if (dead)
{
for (size_t i = 0; i < sizeof CANARY; ++i)
{
byte b = cage[i];
printf(b == CANARY[i] ? "__ " : "%2X ", b);
}
putchar('\n');
}
return dead;
}
enum kind_of_memory {AVAILABLE, TOMBSTONE, NON_ARRAY_MEMORY, ARRAY_MEMORY};
const char* kind_string[] = {0, 0, "non-array memory", " array memory"};
struct metadata
{
byte* address;
size_t size;
kind_of_memory kind;
bool in_use() const
{
return kind & 2;
}
void print() const
{
printf("%s at %p (%d bytes)\n", kind_string[kind], address, size);
}
bool must_keep_searching_for(void* address)
{
return kind == TOMBSTONE || (in_use() && address != this->address);
}
bool canaries_alive() const
{
bool alive = true;
if (canary_dead(address - sizeof CANARY))
{
printf("ERROR: buffer underflow at %p\n", address);
alive = false;
}
if (canary_dead(address + size))
{
printf("ERROR: buffer overflow at %p\n", address);
alive = false;
}
return alive;
}
};
const size_t MINIMUM_CAPACITY = 11;
class hashtable
{
metadata* data;
size_t used;
size_t capacity;
size_t tombstones;
public:
size_t size() const
{
return used - tombstones;
}
void print() const
{
for (size_t i = 0; i < capacity; ++i)
{
if (data[i].in_use())
{
printf(":( leaked ");
data[i].print();
}
}
}
hashtable()
{
used = 0;
capacity = MINIMUM_CAPACITY;
data = static_cast<metadata*>(calloc(capacity, sizeof(metadata)));
tombstones = 0;
}
~hashtable()
{
free(data);
}
hashtable(const hashtable& that)
{
used = 0;
capacity = 3 * that.size() | 1;
if (capacity < MINIMUM_CAPACITY) capacity = MINIMUM_CAPACITY;
data = static_cast<metadata*>(calloc(capacity, sizeof(metadata)));
tombstones = 0;
for (size_t i = 0; i < that.capacity; ++i)
{
if (that.data[i].in_use())
{
insert_unsafe(that.data[i]);
}
}
}
hashtable& operator=(hashtable copy)
{
swap(copy);
return *this;
}
void swap(hashtable& that)
{
my_swap(data, that.data);
my_swap(used, that.used);
my_swap(capacity, that.capacity);
my_swap(tombstones, that.tombstones);
}
void insert_unsafe(const metadata& x)
{
*find(x.address) = x;
++used;
}
void insert(const metadata& x)
{
if (2 * used >= capacity)
{
hashtable copy(*this);
swap(copy);
}
insert_unsafe(x);
}
metadata* find(void* address)
{
size_t index = reinterpret_cast<size_t>(address) % capacity;
while (data[index].must_keep_searching_for(address))
{
++index;
if (index == capacity) index = 0;
}
return &data[index];
}
void erase(metadata* it)
{
it->kind = TOMBSTONE;
++tombstones;
}
} the_hashset;
struct heap_debugger
{
heap_debugger()
{
puts("heap debugger started");
}
~heap_debugger()
{
the_hashset.print();
puts("heap debugger shutting down");
}
} the_heap_debugger;
void* allocate(size_t size, kind_of_memory kind) throw (std::bad_alloc)
{
byte* raw = static_cast<byte*>(malloc(size + 2 * sizeof CANARY));
if (raw == 0) throw std::bad_alloc();
memcpy(raw, CANARY, sizeof CANARY);
byte* payload = raw + sizeof CANARY;
memcpy(payload + size, CANARY, sizeof CANARY);
metadata md = {payload, size, kind};
the_hashset.insert(md);
printf("allocated ");
md.print();
return payload;
}
void release(void* payload, kind_of_memory kind) throw ()
{
if (payload == 0) return;
metadata* p = the_hashset.find(payload);
if (!p->in_use())
{
printf("ERROR: no dynamic memory at %p\n", payload);
}
else if (p->kind != kind)
{
printf("ERROR:wrong form of delete at %p\n", payload);
}
else if (p->canaries_alive())
{
printf("releasing ");
p->print();
free(static_cast<byte*>(payload) - sizeof CANARY);
the_hashset.erase(p);
}
}
}
void* operator new(size_t size) throw (std::bad_alloc)
{
return allocate(size, NON_ARRAY_MEMORY);
}
void* operator new[](size_t size) throw (std::bad_alloc)
{
return allocate(size, ARRAY_MEMORY);
}
void operator delete(void* payload) throw ()
{
release(payload, NON_ARRAY_MEMORY);
}
void operator delete[](void* payload) throw ()
{
release(payload, ARRAY_MEMORY);
}
int main()
{
int* p = new int[1];
delete p; // wrong form of delete
delete[] p; // ok
delete p; // no dynamic memory (double delete)
p = new int[1];
p[-1] = 0xcafebabe;
p[+1] = 0x12345678;
delete[] p; // underflow and overflow prevent release
// p is not released, hence leak
}
推荐答案
非常好，确实。你的金丝雀可以揭示一些真实的溢出/下溢的情况（虽然不是所有的，如Matthieu指出的）。
Very nice, indeed. Your canaries could actually reveal some real cases of overflow/underflow (though not all of them as Matthieu pointed out).
还有什么。您可能会遇到多线程应用程序的一些问题。也许保护哈希表不能同时访问？
What more. You might run into some problems with a multi-threaded application. Perhaps protect the hashtable from concurrent access?
现在你记录每个分配和释放，你可以（如果你喜欢）提供更多有关被测试程序的信息。可能有兴趣知道在任何给定时间的总分配和平均分配数量？
Now that you log every allocation and deallocation, you can (if you like) provide more information about the program being tested. It might be interesting to know the total and average number of allocations at any given time? The total, max, min and average bytes allocated, and the average lifespan of allocations.
如果你想要比较不同的线程，至少使用Pthreads你可以识别它们与分配的总的，最大，最小和平均的字节和分配的平均寿命。 pthread_self（）。这个堆调试器可以成为一个非常有用的分析工具。
If you want to compare different threads, at least with Pthreads you can identify them with pthread_self(). This heap debugger could become a quite useful analysis tool.
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