c語言指針轉換為整數或者整數轉換為指針INT36-C. Converting a pointer to integer or integer to pointer

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An integer may be converted to any pointer type. Except as previously specified, the result is implementation-defined, might not be correctly aligned, might not point to an entity of the referenced type, and might be a trap representation.

Any pointer type may be converted to an integer type. Except as previously specified, the result is implementation-defined. If the result cannot be represented in the integer type, the behavior is undefined. The result need not be in the range of values of any integer type.

The mapping between pointers and integers must be consistent with the addressing structure of the execution environment. Issues may arise, for example, on architectures that have a segmented memory model.

The size of a pointer can be greater than the size of an integer, such as in an implementation where pointers are 64 bits and unsigned integers are 32 bits. This code example is noncompliant on such implementations because the result of converting the 64-bit <code>ptr</code> cannot be represented in the 32-bit integer type:

<code> </code><code>unsigned </code><code>int</code> <code>number = (unsigned </code><code>int</code><code>)ptr;</code>

Any valid pointer to <code>void</code> can be converted to <code>intptr_t</code> or <code>uintptr_t</code> and back with no change in value (seeINT36-EX2). The C Standard guarantees that a pointer to <code>void</code> may be converted to or from a pointer to any object type and back again and that the result must compare equal to the original pointer. Consequently, converting directly from a <code>char *</code> pointer to a <code>uintptr_t</code>, as in this compliant solution, is allowed on implementations that support the <code>uintptr_t</code> type.

<code>#include <stdint.h></code>

<code> </code><code>uintptr_t</code> <code>number = (</code><code>uintptr_t</code><code>)ptr; </code>

In this noncompliant code example, the pointer <code>ptr</code> is converted to an integer value. The high-order 9 bits of the number are used to hold a flag value, and the result is converted back into a pointer. This example is noncompliant on an implementation where pointers are 64 bits and unsigned integers are 32 bits because the result of converting the 64-bit <code>ptr</code> cannot be represented in the 32-bit integer type.

<code>void</code> <code>func(unsigned </code><code>int</code> <code>flag) {</code>

<code> </code><code>number = (number & 0x7fffff) | (flag << 23);</code>

<code> </code><code>ptr = (</code><code>char</code> <code>*)number;</code>

A similar scheme was used in early versions of Emacs, limiting its portability and preventing the ability to edit files larger than 8MB.

This compliant solution uses a <code>struct</code> to provide storage for both the pointer and the flag value. This solution is portable to machines of different word sizes, both smaller and larger than 32 bits, working even when pointers cannot be represented in any integer type.

<code>struct</code> <code>ptrflag {</code>

<code> </code><code>char</code> <code>*pointer;</code>

<code> </code><code>unsigned </code><code>int</code> <code>flag : 9;</code>

<code>} ptrflag;</code>

<code> </code><code>ptrflag.pointer = ptr;</code>

<code> </code><code>ptrflag.flag = flag;</code>

It is sometimes necessary to access memory at a specific location, requiring a literal integer to pointer conversion. In this noncompliant code, a pointer is set directly to an integer constant, where it is unknown whether the result will be as intended:

<code>unsigned </code><code>int</code> <code>*g(</code><code>void</code><code>) {</code>

<code> </code><code>unsigned </code><code>int</code> <code>*ptr = 0xdeadbeef;</code>

<code> </code><code>return</code> <code>ptr;</code>

Adding an explicit cast may help the compiler convert the integer value into a valid pointer. A common technique is to assign the integer to a volatile-qualified object of type <code>intptr_t</code> or <code>uintptr_t</code> and then assign the integer value to the pointer:

<code> </code><code>volatile</code> <code>uintptr_t</code> <code>iptr = 0xdeadbeef;</code>

<code> </code><code>unsigned </code><code>int</code> <code>*ptr = (unsigned </code><code>int</code> <code>*)iptr;</code>

INT36-EX1: A null pointer can be converted to an integer; it takes on the value 0. Likewise, the integer value 0 can be converted to a pointer; it becomes the null pointer.

INT36-EX2: Any valid pointer to <code>void</code> can be converted to <code>intptr_t</code> or <code>uintptr_t</code> or their underlying types and back again with no change in value. Use of underlying types instead of <code>intptr_t</code> or <code>uintptr_t</code> is discouraged, however, because it limits portability.

<code>#include <assert.h></code>

<code> </code><code>intptr_t</code> <code>i = (</code><code>intptr_t</code><code>)(</code><code>void</code> <code>*)&i;</code>

<code> </code><code>uintptr_t</code> <code>j = (</code><code>uintptr_t</code><code>)(</code><code>void</code> <code>*)&j;</code>

<code> </code><code>assert</code><code>(ip == &i);</code>

<code> </code><code>assert</code><code>(jp == &j);</code>

Converting from pointer to integer or vice versa results in code that is not portable and may create unexpected pointers to invalid memory locations.

Rule

Severity

Likelihood

Remediation Cost

Priority

Level

INT36-C

Low

Probable

High

Tool

Version

Checker

Description

<a href="https://www.securecoding.cert.org/confluence/display/seccode/Rose" target="_blank">Compass/ROSE</a>

<a href="https://www.securecoding.cert.org/confluence/display/seccode/Coverity" target="_blank">Coverity</a>

6.5

POINTER_CONVERSION_LOSES_BITS

Fully Implemented

<a href="https://www.securecoding.cert.org/confluence/display/seccode/CERT+C+Rules+implemented+in+the+LDRA+tool+suite" target="_blank">LDRA tool suite</a>

8.5.4

94 S

Fully implemented

v8.2

305, 306, 309, 674

Partially implemented

<a href="https://www.securecoding.cert.org/confluence/pages/viewpage.action?pageId=637" target="_blank">CERT C++ Coding Standard</a>

<a href="https://www.securecoding.cert.org/confluence/display/cplusplus/INT11-CPP.+Take+care+when+converting+from+pointer+to+integer+or+integer+to+pointer" target="_blank">INT11-CPP. Take care when converting from pointer to integer or integer to pointer</a>

Pointer Casting and Pointer Type Changes [HFC]

Converting a pointer to integer or integer to pointer [intptrconv]

<a href="http://cwe.mitre.org/" target="_blank">MITRE CWE</a>

6.3.2.3, "Pointers"

本文轉自fatshi51CTO部落格，原文連結：http://blog.51cto.com/duallay/1871615 ，如需轉載請自行聯系原作者

c語言指針轉換為整數或者整數轉換為指針INT36-C. Converting a pointer to integer or integer to pointer

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c語言 指針轉換為整數或者 整數轉換為指針INT36-C. Converting a pointer to integer or integer to pointer

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c語言指針轉換為整數或者整數轉換為指針INT36-C. Converting a pointer to integer or integer to pointer