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This PR adds a detailed Configuration.md document that comprehensively explains the Compiler Explorer configuration system. It covers: - Configuration file structure and hierarchical loading - Property types and automatic conversions - List separators and specialized formats - Group inheritance and compiler configuration - Variable substitution mechanisms - Advanced features like remote compilers and property debugging Additionally, it updates all related documentation to reference this central document for configuration details, reducing duplication and ensuring consistency. This document will serve as the foundation for future configuration system improvements by providing clear documentation of the current implementation.
92 lines
4.6 KiB
Markdown
92 lines
4.6 KiB
Markdown
# About LD_LIBRARY_PATH and library paths
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## Background
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Libraries are hard. Libraries can be needed for user code, but also to run compilers.
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For CE we use a lot of different compilers and environments that need to be separated from the OS's installation, and
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that makes things more complicated than just building with your standard OS's compiler.
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Including header files or equivalent is usually the easy part. If there are binaries involved, things get complicated.
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We have a couple of separate stages where we use and mix different techniques to be able to produce the right assembly
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or executables.
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- Compilation without linking
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- The `LD_LIBRARY_PATH` environment variable is used here to enable the compiler to find the `.so` files that they
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need to run.
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- If you're running a local installation, this is usually your own systems' `LD_LIBRARY_PATH` plus extra things that
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CE adds through properties.
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- On godbolt.org we always start with an empty `LD_LIBRARY_PATH` and add what is set in the properties.
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- Building an executable or binary
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- We use `-Wl,-rpath=` (or equivalent `rpathFlag`) to force library paths into the executable so that they will always
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find the same `.so` files no matter where they are run. Usually this also includes lib64 and lib folders that the
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compiler offers for standard libraries that the toolchain offers.
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- Library paths supplied through `-Wl,-rpath=` for shared libraries will be able to dynamically link to the right
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architecture's `.so` even if multiple paths are given that contain the same `.so` file.
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- We use `-L` (or equivalent `libpathFlag`) to enable the compiler to find both static (`.a`) and shared (`.so`)
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libraries.
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- We always add '.' as a path as well because that's where we put libraries that are downloaded from our Conan server.
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- We use `-l` (or equivalent `linkFlag`) to say we want to statically or dynamically link to a named library binary
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(the compiler and linker decide if it's gonna be static or dynamic).
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- Running the executable
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- We use `LD_LIBRARY_PATH` just in case these are dependencies inherited from the compiler - and for the libraries
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that are used (also just in case).
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## Specific properties that are used in certain situations
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For a comprehensive overview of the configuration system, see [Configuration.md](Configuration.md).
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- Compiler .ldPath
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- is used for `LD_LIBRARY_PATH` to support running the compiler
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- is used for linking (`-Wl,-rpath=` and/or `-L`) during building binaries
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- is used for `LD_LIBRARY_PATH` to enable the users's executable to find `.so` files
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- Compiler .libPath
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- is used for linking (`-Wl,-rpath=` and/or `-L`) during building binaries
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- is used for `LD_LIBRARY_PATH` to enable the users's executable to find `.so` files
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- Library .libPath
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- is used for linking (`-Wl,-rpath=` and/or `-L`) during building binaries
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- is used for `LD_LIBRARY_PATH` to enable the users's executable to find `.so` files (just in case)
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## Example
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Say we have the following things in a `c++.local.properties` file:
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```INI
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compilers=mycl
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compiler.mycl.exe=/home/ubuntu/mycl/bin
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compiler.mycl.ldPath=/home/ubuntu/mycl/lib/lib64
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compiler.mycl.libPath=/home/ubuntu/mycl/lib/lib64:/home/ubuntu/mycl/lib/lib32
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compiler.mycl.options=--gcc-toolchain=/home/ubuntu/gcc10
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compiler.mycl.includeFlag=-I
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libs=mylib
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libs.mylib.name=My library
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libs.mylib.path=/home/ubuntu/mylib/include
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libs.mylib.libpath=/home/ubuntu/mylib/lib
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libs.mylib.staticliblink=mylib
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```
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This will result in the following situations if we want to compile some code with both the mycl compiler and the mylib
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library:
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- Compilation without linking
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- `LD_LIBRARY_PATH` is set to `/home/ubuntu/mycl/lib/lib64`
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- `-I/home/ubuntu/mylib/include` is added to the compilation arguments
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- Building an executable or binary
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- `LD_LIBRARY_PATH` is set to `/home/ubuntu/mycl/lib/lib64`
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- The following are added to the compilation arguments
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- `-I/home/ubuntu/mylib/include` (library include path)
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- `-Wl,-rpath=/home/ubuntu/mycl/lib/lib64` (compiler library paths)
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- `-Wl,-rpath=/home/ubuntu/mycl/lib/lib32`
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- `-Wl,-rpath=.` (conan library path)
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- `-L.`
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- `-Wl,-rpath=/home/ubuntu/gcc10/lib/lib` (gcc toolchain library paths)
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- `-Wl,-rpath=/home/ubuntu/gcc10/lib/lib32`
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- `-Wl,-rpath=/home/ubuntu/gcc10/lib/lib64`
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- `-Wl,-rpath=/home/ubuntu/mylib/lib` (mylib library path - just in case there are `.so` files used)
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- `-L/home/ubuntu/mylib/lib` (mylib library path used to find `libmylib.a`)
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- `-lmylib` (mylib library name)
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- Running the executable
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- `LD_LIBRARY_PATH` is set to `/home/ubuntu/mycl/lib/lib64:/home/ubuntu/mycl/lib/lib32:/home/ubuntu/mylib/lib`
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