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| <h3 class="section">4.5 Static Variables</h3> |
| |
| <p>Initialized static variables are represented by the ‘<samp><span class="samp">S</span></samp>’ and |
| ‘<samp><span class="samp">V</span></samp>’ symbol descriptors. ‘<samp><span class="samp">S</span></samp>’ means file scope static, and |
| ‘<samp><span class="samp">V</span></samp>’ means procedure scope static. One exception: in XCOFF, IBM's |
| xlc compiler always uses ‘<samp><span class="samp">V</span></samp>’, and whether it is file scope or not |
| is distinguished by whether the stab is located within a function. |
| |
| <!-- This is probably not worth mentioning; it is only true on the sparc --> |
| <!-- for `double' variables which although declared const are actually in --> |
| <!-- the data segment (the text segment can't guarantee 8 byte alignment). --> |
| <!-- (although GCC --> |
| <!-- 2.4.5 has a bug in that it uses @code{N_FUN}, so neither dbx nor GDB can --> |
| <!-- find the variables) --> |
| <p><a name="index-N_005fSTSYM-37"></a><a name="index-N_005fLCSYM-38"></a><a name="index-N_005fFUN_002c-for-variables-39"></a><a name="index-N_005fROSYM-40"></a>In a.out files, <code>N_STSYM</code> means the data section, <code>N_FUN</code> |
| means the text section, and <code>N_LCSYM</code> means the bss section. For |
| those systems with a read-only data section separate from the text |
| section (Solaris), <code>N_ROSYM</code> means the read-only data section. |
| |
| <p>For example, the source lines: |
| |
| <pre class="example"> static const int var_const = 5; |
| static int var_init = 2; |
| static int var_noinit; |
| </pre> |
| <p class="noindent">yield the following stabs: |
| |
| <pre class="example"> .stabs "var_const:S1",36,0,0,_var_const # <span class="roman">36 is N_FUN</span> |
| ... |
| .stabs "var_init:S1",38,0,0,_var_init # <span class="roman">38 is N_STSYM</span> |
| ... |
| .stabs "var_noinit:S1",40,0,0,_var_noinit # <span class="roman">40 is N_LCSYM</span> |
| </pre> |
| <p><a name="index-C_005fSTSYM-41"></a><a name="index-C_005fBSTAT-42"></a><a name="index-C_005fESTAT-43"></a>In XCOFF files, the stab type need not indicate the section; |
| <code>C_STSYM</code> can be used for all statics. Also, each static variable |
| is enclosed in a static block. A <code>C_BSTAT</code> (emitted with a |
| ‘<samp><span class="samp">.bs</span></samp>’ assembler directive) symbol begins the static block; its |
| value is the symbol number of the csect symbol whose value is the |
| address of the static block, its section is the section of the variables |
| in that static block, and its name is ‘<samp><span class="samp">.bs</span></samp>’. A <code>C_ESTAT</code> |
| (emitted with a ‘<samp><span class="samp">.es</span></samp>’ assembler directive) symbol ends the static |
| block; its name is ‘<samp><span class="samp">.es</span></samp>’ and its value and section are ignored. |
| |
| <p>In ECOFF files, the storage class is used to specify the section, so the |
| stab type need not indicate the section. |
| |
| <p>In ELF files, for the SunPRO compiler version 2.0.1, symbol descriptor |
| ‘<samp><span class="samp">S</span></samp>’ means that the address is absolute (the linker relocates it) |
| and symbol descriptor ‘<samp><span class="samp">V</span></samp>’ means that the address is relative to the |
| start of the relevant section for that compilation unit. SunPRO has |
| plans to have the linker stop relocating stabs; I suspect that their the |
| debugger gets the address from the corresponding ELF (not stab) symbol. |
| I'm not sure how to find which symbol of that name is the right one. |
| The clean way to do all this would be to have the value of a symbol |
| descriptor ‘<samp><span class="samp">S</span></samp>’ symbol be an offset relative to the start of the |
| file, just like everything else, but that introduces obvious |
| compatibility problems. For more information on linker stab relocation, |
| See <a href="ELF-Linker-Relocation.html#ELF-Linker-Relocation">ELF Linker Relocation</a>. |
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