mirror of
https://github.com/matrix-construct/construct
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66 lines
2.1 KiB
Markdown
66 lines
2.1 KiB
Markdown
# Module Tree
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This directory contains dynamically loadable functionality to libircd.
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#### Approach
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Unlike most of the module systems found in traditional C free software
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projects, our approach is oriented around *global symbol* availability to the
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address space rather than explicit imports from self-contained modules. This
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direction is made viable by C++ and advances in the compiler and linker
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toolchains. The result is significantly simpler and more convenient for
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developers to work with.
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##### GLOBAL SYMBOLS
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Modules are loaded with `RTLD_GLOBAL` on both posix and windows platforms.
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Use of C++ namespaces, visibility attributes, `STB_GNU_UNIQUE`, etc are
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adequate to make this modernization.
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##### WEAK UNDEFINED SYMBOLS
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All project code is built to silently weaken undefined symbols. This means
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a complicated interface declared in a header, like a class interface with
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public and private and static members (typical in C++) can be included
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by itself into any part of the project without knowing where the definitions
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of that interface are until they are *first used* at runtime.
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If definitions are not available because they are in an unloaded module: a C++
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exception is thrown directly from the callsite. We have built this action
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is built into the lookup mechanism of the runtime dynamic linker; none of
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this requires knowledge or effort from developers to use.
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#### Layout
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(TODO)
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## Getting started
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The header `mods/mapi.h` is specific to modules and included for modules in
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addition to the core `ircd.h`. Both of these are included automatically
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via the compiler's command-line and the developer does not have to `#include`
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either in the module.
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1. Every loadable module requires a static `ircd::mapi::header` with the explicit
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name of `IRCD_MODULE`. This is an object which will be sought by the module
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loader in libircd.
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```
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// Example of a trivial module
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ircd::mapi::header
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IRCD_MODULE
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{
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"My Module", []
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{
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puts("hi\n");
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}
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};
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```
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2. Add an `_la_SOURCES` entry for your module in the appropriate place in
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Makefile.am.
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3. Add the module `.la` name to the appropriate LTLIBRARIES list
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in Makefile.am.
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