如何从通用函数符号计算或指定COFF符号Table的"value"？

Question

我正在像汇编程序一样开发nasm，现在我正在编写一个生成 COFF 格式文件的过程。

我的问题非常具体，我在 COFF Symbol Table 上遇到了名为 value 的字段。我找不到计算或指定它的方法。

我阅读了文档Microsoft Portable Executable and Common Object File Format Specification。关注一篇文章，这是我参考的：

The Symbol Table described in this section is inherited from the traditional COFF format.
It is distinct from CodeView® information. A file may contain both a COFF Symbol
Table and CodeView debug information, and the two are kept separate. Some Microsoft
tools use the Symbol Table for limited but important purposes, such as communicating
COMDAT information to the linker. Section names and file names, as well as code and
data symbols, are listed in the Symbol Table.
The location of the Symbol Table is indicated in the COFF Header.
The Symbol Table is an array of records, each 18 bytes long. Each record is either a
standard or auxiliary symbol-table record. A standard record defines a symbol or name,
and has the following format:

|--------| -----|---------------|-------------------------------------------------------------------|
| Offset | Size | Field         | Description                                                       |
|--------| -----|---------------|-------------------------------------------------------------------|
| 0      | 8    | Name (*)      | Name of the symbol, represented by union of three structures.     |
|        |      |               | An array of eight bytes is used if the name is not more than      |
|        |      |               | eight bytes long. See Section 5.4.1,                              |
|        |      |               | "Symbol Name Representation, " for more information.              |
----------------------------------------------------------------------------------------------------|
| 8      | 4    | Value         | Value associated with the symbol.                                 |
|        |      |               | The interpretation of this field depends on Section Number        |
|        |      |               | and Storage Class. A typical meaning is the relocatable address.  |
----------------------------------------------------------------------------------------------------|
| 12     | 2    | SectionNumber | Signed integer identifying the section, using a one-based index   |
|        |      |               | into the Section Table. Some values have special meaning defined  |
|        |      |               | in "Section Number Values."                                       |
----------------------------------------------------------------------------------------------------|
| 14     | 2    | Type          | representing type. Microsoft tools set this field to 0x20         |
|        |      |               | (function) or 0x0 (not a function). See Section 5.4.3,            |
|        |      |               | "Type Representation," for more information.                      |
----------------------------------------------------------------------------------------------------|
| 16     | 1    | StorageClass  | Enumerated value representing storage class.                      |
|        |      |               | See Section 5.4.4, "Storage Class," for more information.         |
|        |      |               |                                                                   |
----------------------------------------------------------------------------------------------------|
| 17     | 1    | NumberOfAux   | Number of auxiliary symbol table entries that follow this record. |
|        |      | Symbols       |                                                                   |
----------------------------------------------------------------------------------------------------|

我想知道如何指定Value字段来定义基本的C函数符号，例如_test

// define basic C function, I think it will be the symbol like "_test" in COFF files.
void test(int value) { return;}

这个文件说Value字段代表relocatable address。怎么知道的？

Answer 1

终于明白value字段的意义了

该字段表示从符号table开始的偏移值。 如果一个符号和另一个符号之间有任何机器码，这个值应该包含那些字节大小。