This patch implements the initial support for upstreaming
[llubi](https://github.com/dtcxzyw/llvm-ub-aware-interpreter). It only
provides the minimal functionality to run a simple main function. I hope
we can focus on the interface design in this PR, rather than trivial
implementations for each instruction.
RFC link:
https://discourse.llvm.org/t/rfc-upstreaming-llvm-ub-aware-interpreter/89645
Excluding the driver `llubi.cpp`, this patch contains three components
for better decoupling:
+ `Value.h/cpp`: Value representation
+ `Context.h/cpp`: Global state management (e.g., memory) and
interpreter configuration
+ `Interpreter.cpp`: The main interpreter loop
Compared to the out-of-tree version, the major differences are listed
below:
+ The interpreter logic always returns the control to its caller, i.e.,
it never calls `exit/abort` when immediate UBs are triggered.
+ `EventHandler` provides an interface to dump the trace. It also allows
callers to inspect the actual value and verify the correctness of
analysis passes (e.g, KnownBits/SCEV).
+ The context is designed to be reentrant. That is, you can call
`runFunction` multiple times. But its usefulness remains in doubt due to
side effects made by previous calls.
+ `runFunction` handles function calls with a loop, instead of calling
itself recursively. This makes it no longer bounded by the stack depth.
+ Uninitialized memory is planned to be approximated by returning random
values each time an uninitialized byte is loaded.
LLVM Documentation
==================
LLVM's documentation is written in reStructuredText, a lightweight
plaintext markup language (file extension `.rst`). While the
reStructuredText documentation should be quite readable in source form, it
is mostly meant to be processed by the Sphinx documentation generation
system to create HTML pages which are hosted on <https://llvm.org/docs/> and
updated after every commit. Manpage output is also supported, see below.
If you instead would like to generate and view the HTML locally, install
Sphinx <http://sphinx-doc.org/> and then do:
cd <build-dir>
cmake -DLLVM_ENABLE_SPHINX=true -DSPHINX_OUTPUT_HTML=true <src-dir>
make -j3 docs-llvm-html
$BROWSER <build-dir>/docs/html/index.html
The mapping between reStructuredText files and generated documentation is
`docs/Foo.rst` <-> `<build-dir>/docs//html/Foo.html` <-> `https://llvm.org/docs/Foo.html`.
If you are interested in writing new documentation, you will want to read
`SphinxQuickstartTemplate.rst` which will get you writing documentation
very fast and includes examples of the most important reStructuredText
markup syntax.
Manpage Output
===============
Building the manpages is similar to building the HTML documentation. The
primary difference is to use the `man` makefile target, instead of the
default (which is `html`). Sphinx then produces the man pages in the
directory `<build-dir>/docs/man/`.
cd <build-dir>
cmake -DLLVM_ENABLE_SPHINX=true -DSPHINX_OUTPUT_MAN=true <src-dir>
make -j3 docs-llvm-man
man -l <build-dir>/docs/man/FileCheck.1
The correspondence between .rst files and man pages is
`docs/CommandGuide/Foo.rst` <-> `<build-dir>/docs//man/Foo.1`.
These .rst files are also included during HTML generation so they are also
viewable online (as noted above) at e.g.
`https://llvm.org/docs/CommandGuide/Foo.html`.
Checking links
==============
The reachability of external links in the documentation can be checked by
running:
cd llvm/docs/
sphinx-build -b linkcheck . _build/lintcheck/
# report will be generated in _build/lintcheck/output.txt
Doxygen page Output
==============
Install doxygen <https://www.doxygen.nl/download.html> and dot2tex <https://dot2tex.readthedocs.io/en/latest>.
cd <build-dir>
cmake -DLLVM_ENABLE_DOXYGEN=On <llvm-top-src-dir>
make doxygen-llvm # for LLVM docs
make doxygen-clang # for clang docs
It will generate html in
<build-dir>/docs/doxygen/html # for LLVM docs
<build-dir>/tools/clang/docs/doxygen/html # for clang docs
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