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| <h3 class="section">2.3 Names of Include Files</h3> |
| |
| <p>There are several schemes for dealing with include files: the |
| traditional <code>N_SOL</code> approach, Sun's <code>N_BINCL</code> approach, and the |
| XCOFF <code>C_BINCL</code> approach (which despite the similar name has little in |
| common with <code>N_BINCL</code>). |
| |
| <p><a name="index-N_005fSOL-4"></a>An <code>N_SOL</code> symbol specifies which include file subsequent symbols |
| refer to. The string field is the name of the file and the value is the |
| text address corresponding to the end of the previous include file and |
| the start of this one. To specify the main source file again, use an |
| <code>N_SOL</code> symbol with the name of the main source file. |
| |
| <p><a name="index-N_005fBINCL-5"></a><a name="index-N_005fEINCL-6"></a><a name="index-N_005fEXCL-7"></a>The <code>N_BINCL</code> approach works as follows. An <code>N_BINCL</code> symbol |
| specifies the start of an include file. In an object file, only the |
| string is significant; the linker puts data into some of the other |
| fields. The end of the include file is marked by an <code>N_EINCL</code> |
| symbol (which has no string field). In an object file, there is no |
| significant data in the <code>N_EINCL</code> symbol. <code>N_BINCL</code> and |
| <code>N_EINCL</code> can be nested. |
| |
| <p>If the linker detects that two source files have identical stabs between |
| an <code>N_BINCL</code> and <code>N_EINCL</code> pair (as will generally be the case |
| for a header file), then it only puts out the stabs once. Each |
| additional occurrence is replaced by an <code>N_EXCL</code> symbol. I believe |
| the GNU linker and the Sun (both SunOS4 and Solaris) linker are the only |
| ones which supports this feature. |
| |
| <p>A linker which supports this feature will set the value of a |
| <code>N_BINCL</code> symbol to the total of all the characters in the stabs |
| strings included in the header file, omitting any file numbers. The |
| value of an <code>N_EXCL</code> symbol is the same as the value of the |
| <code>N_BINCL</code> symbol it replaces. This information can be used to |
| match up <code>N_EXCL</code> and <code>N_BINCL</code> symbols which have the same |
| filename. The <code>N_EINCL</code> value, and the values of the other and |
| description fields for all three, appear to always be zero. |
| |
| <p><a name="index-C_005fBINCL-8"></a><a name="index-C_005fEINCL-9"></a>For the start of an include file in XCOFF, use the <samp><span class="file">.bi</span></samp> assembler |
| directive, which generates a <code>C_BINCL</code> symbol. A <samp><span class="file">.ei</span></samp> |
| directive, which generates a <code>C_EINCL</code> symbol, denotes the end of |
| the include file. Both directives are followed by the name of the |
| source file in quotes, which becomes the string for the symbol. |
| The value of each symbol, produced automatically by the assembler |
| and linker, is the offset into the executable of the beginning |
| (inclusive, as you'd expect) or end (inclusive, as you would not expect) |
| of the portion of the COFF line table that corresponds to this include |
| file. <code>C_BINCL</code> and <code>C_EINCL</code> do not nest. |
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