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POHow to get a pointer to a binary section in MSVC?
 

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  1. POHow to get a pointer to a binary section in MSVC?
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    <p>I'm writing some code which stores some data structures in a special named binary section. These are all instances of the same struct which are scattered across many C files and are not within scope of each other. By placing them all in the named section I can iterate over all of them.</p> <p>In GCC, I use _<em>attribute</em>_((section(...)) plus some specially named extern pointers which are magically filled in by the linker. Here's a trivial example:</p> <pre><code>#include &lt;stdio.h&gt; extern int __start___mysection[]; extern int __stop___mysection[]; static int x __attribute__((section("__mysection"))) = 4; static int y __attribute__((section("__mysection"))) = 10; static int z __attribute__((section("__mysection"))) = 22; #define SECTION_SIZE(sect) \ ((size_t)((__stop_##sect - __start_##sect))) int main(void) { size_t sz = SECTION_SIZE(__mysection); int i; printf("Section size is %u\n", sz); for (i=0; i &lt; sz; i++) { printf("%d\n", __start___mysection[i]); } return 0; } </code></pre> <p>I'm trying to figure out how to do this in MSVC but I'm drawing a blank. I see from the compiler documentation that I can declare the section using __pragma(section(...)) and declare data to be in that section with __declspec(allocate(...)) but I can't see how I can get a pointer to the start and end of the section at runtime.</p> <p>I've seen some examples on the web related to doing _<em>attribute</em>_((constructor)) in MSVC, but it seems like hacking specific to CRT and not a general way to get a pointer to the beginning/end of a section. Anyone have any ideas?</p>
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    1. USAndrew B.
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    1. COMay I ask why you want to control binary section naming in the first place?
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    2. COIt's for a high-performance instrumentation framework. Imagine a printf(format, args...) invocation, where all the format strings were stored in the binary section, and the only thing that gets logged is the arguments plus a lookup value. The argument substitution takes place in post-processing.
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      1. POHow to get a pointer to a binary section in MSVC?
      1. USAndrew B.
    3. COA better example of this is a program that allows you to add modules by relinking rather than recompiling (and possibly regenerating some code). If you can treat the entire section as an array of some struct then you can iterate over it and perform some action on/for each entry, such as call `cur_entry[i]->init(&cur_entry)`. You can also use special knowledge about memory usage patterns to optimize for paging and cache locality by doing this. Not usually Windows related (that I know of) but this can also be required for Harvard architecture processors.
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