[PATCH] D11072: Implement tool to convert bitcode to text.

[Rafael Espíndola]

If we are going to have this (not convinced we should), it should be
another library and not modify lib/Bitcode.


On 9 July 2015 at 14:06, Karl Schimpf <kschimpf at google.com> wrote:
> kschimpf created this revision.
> kschimpf added reviewers: jvoung, dschuff.
> kschimpf added a subscriber: llvm-commits.
> Herald added a subscriber: jfb.
>
> Provide a new tool for LLVM bitcode files that makes it easier to test
> and fuzz. That is, a simple textual form that captures the contents of
> binary bitcode files.
>
> The textual form removes all references to abbreviations in the binary
> bitcode file. This is done to simplify its form.
>
> A textual bitcode record is a sequence of (unsigned) integers,
> separated by commas, and terminated with a semicolin. Each bitcode
> record appears on a separate line.
>
> The tool llvm-bcanalyzer also provides a textual version of bitcode
> files. However, it doesn't provide anyway to convert the output back
> to a binary bitcode file. It is also much more complex.
>
> Besides providing a command line tool, it set up for use with lit
> (LLVM Integrated Tester). Invalid bitcode tests, that don't
> corresponding to abbreviations and bitstream issues, can be written as
> a text file. This text file can run tests and check the results using
> FileCheck.
>
> The use of textual bitcode files (unlike the current invalid bitcode
> tests) can use a single file to describe the invalid test. It also has
> the advantage of being easier to port if the format of bitcode records
> change. In such cases, you only need to edit the problematic textual
> bitcode records that have changed since the test was added. Current
> tests are in binary form, and very difficult to figure out how to
> change when the bitcode format changes.
>
> For fuzzing, the text form is easy to model using tokens (the digits,
> separator ',', and terminator ';\n'). This allows (local) mutations to
> easily be formed by existing fuzzers (such as afl-fuzz) without
> modification. The textual-to-binary conversion methods can be used as
> a post-processor of the fuzzer, or as a preprocessor to the llvm tool
> being tested.
>
> The motivation for this tool has been the success PNaCl
> (www.gonacl.com) has had in testing its tools, as well as the ease of
> generating invalid test cases.
>
> http://reviews.llvm.org/D11072
>
> Files:
>   include/llvm/Bitcode/BitcodeConvert.h
>   lib/Bitcode/Reader/BitcodeRecordReader.cpp
>   lib/Bitcode/Reader/CMakeLists.txt
>   lib/Bitcode/Writer/BitcodeRecordWriter.cpp
>   lib/Bitcode/Writer/CMakeLists.txt
>   test/Bitcode/text-bitcode.ll
>   test/lit.cfg
>   tools/LLVMBuild.txt
>   tools/Makefile
>   tools/llvm-bcconv/CMakeLists.txt
>   tools/llvm-bcconv/LLVMBuild.txt
>   tools/llvm-bcconv/Makefile
>   tools/llvm-bcconv/llvm-bcconv.cpp
>
>
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