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AddingACompiler.md

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Adding a new compiler

This document explains how to add a new compiler to Compiler Explorer ("CE" from here on), first for a local instance, and then how to submit PRs to get it into the main CE site.

Configuration

Compiler configuration is done through the etc/config/c++.*.properties files (for C++, other languages follow the obvious pattern, replace as needed for your case).

The various named configuration files are used in different contexts: for example etc/config/c++.local.properties take priority over etc/config/c++.defaults.properties. The local version is ignored by git, so you can make your own personalised changes there. The live site uses the etc/config/c++.amazon.properties file.

Within the file, configuration is a set of key and value pairs, separated by an =. Whitespace is not trimmed. Lines starting with # are considered comments and not parsed. The list of compilers is set by the compilers key and is a list of compiler identifiers or groups, separated by colons. Group names have an & prepended. As a nod to backwards compatibility with very old configurations, a path to a compiler can also be put in the list, but that doesn't let you configure many aspects of the compiler, nor does it allow paths with colons in them (since these are used as separators). The identifier itself is not important, but must be unique to that compiler.

An example configuration:

compilers=gcc620:gcc720:&clang

This says there are two compilers with identifiers gcc620 and gcc720, and a group of compilers called clang. For the compilers, CE will look for some keys named compiler.ID.name and compiler.ID.exe (and some others, detailed later). The ID is the identifier of the compiler being looked up. The name value is used as the human-readable compiler name shown to users, and the exe should be the path name of the compiler executable.

For example:

compiler.gcc620.name=GCC 6.2.0
compiler.gcc620.exe=/usr/bin/gcc-6.2.0
compiler.gcc720.name=GCC 7.2.0
compiler.gcc720.exe=/usr/bin/gcc-7.2.0

In addition to the name and exe per-compiler configuration keys, there are also some other options. Most of them default to sensible values for GCC-like compilers.

A group is defined similar to a list of compilers, and may contain other groups. Keys for groups start with group.ID. Configuration keys applied to the group apply to all compilers in that group (unless overridden by the compiler itself). An example:

group.clang.compilers=clang4:clang5
group.clang.intelAsm=-mllvm -x86-asm-syntax=intel
compiler.clang4.name=Clang 4
compiler.clang4.exe=/usr/bin/clang4
compiler.clang5.name=Clang 5
compiler.clang5.exe=/usr/bin/clang5

Note about configuration files hierarchy:

As mentioned previously, the live site uses etc/config/c++.amazon.properties to load its configuration from, but for properties not defined in the amazon file, the values present in etc/config/c++.defaults.properties will be used.

By design, this does not however work for groups (Nor any other nested property). That is, if in etc/config/c++.defaults.properties you define the intelAsm property as:

versionFlag=--version
compilers=&clang
group.clang.intelAsm=-mllvm -x86-asm-syntax=intel
group.clang.groupName=Clang
...

but etc/config/c++.amazon.properties only has:

compilers=&clang
group.clang.groupName=Clang
...

once the site runs on the Amazon environment, the &clang group will not have the intelAsm property set, but versionFlag will.

Configuration keys

Key Name Type Description
name String Human readable name of the compiler
exe Path Path to the executable
alias Identifier Another identifier for this compiler (mostly deprecated, used for backwards compatibility with very old CE URLs)
options String Additional compiler options passed to the compiler when running it
intelAsm String Flags used to select intel assembly format (if not detected automatically)
needsMulti Boolean Whether the compiler needs multi arch support (defaults to yes if the host has multiarch enabled)
supportsBinary Boolean Whether this compiler supports linking to binary (e.g. compile, assemble and link to final executable program)
supportsBinaryObject Boolean Whether this compiler supports compiling to binary object (e.g. compile and assemble to binary object)
supportsExecute Boolean Whether binary output from this compiler can be executed
versionFlag String The flag to pass to the compiler to make it emit its version
versionRe RegExp A regular expression used to capture the version from the version output
compilerType String The name of the class handling this compiler
interpreted Boolean Whether this is an interpreted language, and so the "compiler" is really an interpreter
executionWrapper Path Path to script that can execute the compiler's output (e.g. could run under qemu or mpi_run or similar)
executionWrapperArgs String List of arguments passed to the execution wrapper (separated by | character)
demangler String Path to the demangler tool
demanglerArgs String List of arguments passed to the demangler binary (separated by | character)
objdumper String Path to the object dump tool
objdumperArgs String List of arguments passed to the object dump tool (separated by | character)
instructionSet String The default set for the compiler, it will fall into that group of compilers (so you can filter by it) and get different instruction set documentation if available

The compilerType option is special: it refers to the Javascript class in lib/compilers/*.ts which handles running and handling output for this compiler type.

Adding a new compiler locally

It should be pretty straightforward to add a compiler of your own. Create a etc/config/c++.local.properties file and override the compilers list to include your own compiler, and its configuration.

Once you've done that, running make should pick up the configuration and during startup you should see your compiler being run and its version being extracted. If you don't, check for any errors, and try running with make EXTRA_ARGS='--debug' to see (a lot of) debug output.

If you're looking to add other language compilers for another language, obviously create the etc/config/LANG.local.properties in the above steps, and run with make EXTRA_ARGS='--language LANG' (e.g. etc/config/rust.local.properties and make EXTRA_ARGS='--language Rust').

Test locally, and for many compilers that's probably all you need to do. Some compilers might need a few options tweaks (like the intel asm setting, or the version flag). For a completely new compiler, you might need to define a whole new compilerType. Doing so is beyond this document's scope at present, but take a look inside lib/compilers/ to get some idea what might need to be done.

Adding a new compiler running remotely to your locally built compiler explorer

If you would like to have both gcc and MSVC running in the "same" compiler explorer, one option would be running gcc on your local Linux machine and add a proxy to the MSVC compiler, which is running on a remote Window host. To achieve this, you could

  • Setup compiler explorer on your Linux host as usual
  • Follow this guide to set up another compiler explorer instance on your Windows host
  • Add your Windows compiler explorer as a proxy to your Linux compiler explorer. You can simply modify your etc/config/c++.local.properties on your Linux host
compilers=&gcc:&clang:myWindowsHost@10240

Yes it is the @ symbol rather than the : before the port number. Restart the Linux compiler explorer, and you will be able to see the MSVC compiler in the compiler list.

Adding a new compiler to the live site

On the main CE website, compilers are installed into a /opt/compiler-explorer/ directory by a set of scripts in the sister GitHub repo: https://github.com/compiler-explorer/infra

In the update_compilers directory in that repository are a set of scripts that download and install binaries and compilers. If you wish to test locally, and can create a /opt/compiler-explorer directory on your machine which is readable and writable by your current user, then you can run the scripts directly. The binaries and the free compilers can be installed - the commercial compilers live in the install_nonfree_compilers.sh and won't work.

If your compiler fits nicely into the harness then it should be straightforward to add it there. Anything more complex: contact the CE authors for more help.

Putting it all together

Hopefully that's enough to get an idea. The ideal case of a GCC-like compiler should be a pull request to add a couple of lines to the infra repository to install the compiler, and a pull request to add a few lines to the LANG.amazon.properties file in this repository.

If you feel like we could improve this document in any way, please contact us. We'd love to hear from you!