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Transition-to-CMake.md

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Transition to CMake

In August 2017, several incompatible changes were merged into the libsnark master branch:

Transitioned to CMake

We upgraded libsnark’s build process from a shell script and Makefile for installation and compilation to a new CMake-based process (https://cmake.org/). We are making this transition to better address the growing system-level and modularity needs of libsnark.

Factored out algebraic routines into new libraries

We have factored out core algebraic components of libsnark to allow developers to use internal classes and functions that are useful in applications beyond libsnark, as well as to simplify the growing directory structure of libsnark.

The two new libraries are:

  • libff for finite fields and elliptic curves
  • libfqfft for fast polynomial evaluation and interpolation in various finite domains

These libraries are now automatically fetched and installed as Git submodules, in the “depends” (formerly: “third-party”) directory.

Monolithic version of libsnark is archived and unsupported

As part of this transition, we will maintain a copy of the deprecated version under the monolithic branch. However, we will not support any future development work for the monolithic branch. Should a critical vulnerability be found in monolithic, we will patch it accordingly.

Transition Notes

See the the Building section of README.md for the new build instructions.

The compile flags are mostly analogous, but use different and more consistent notation (e.g., instead of make OPTFLAGS=... use cmake -DOPT_FLAGS=... && make. Notable changes:

  • Use cmake -DCURVE=curvename .. instead of the old make CURVE=curvename.
  • Use cmake -DLOWMEM=ON/OFF .. instead of the old make LOWMEM=1/0. Similarly for MULTICORE, MONTGOMERY_OUTPUT, USE_ASM, USE_MIXED_ADDITION and PERFORMANCE. (The defaults are unchanged.)
  • Binary output is now enabled by default; use cmake -DBINARY_OUTPUT=OFF .. to disable it for streaming-format compatibility with the old default.
  • Use cmake -DUSE_PT_COMPRESSION=OFF .. instead of defining NO_PT_COMPRESSION (but the default is still to use point compression).
  • Use cmake -DWITH_PROCPS=OFF .. instead of the old make NO_PROCPS=1 flag (but the default is still to use procps). Similarly for SUPERCOP.
  • Removed NO_GTEST (that was used to skip tests that use the Google Test library).
  • The new DEPENDS_DIR flag customizes the dependencies installation directory.

Handling dependencies shared with submodules

The following explains how we handles dependencies shared with submodules; you may need to understand this if you modify these submodules.

The depends folder (formerly third-party) includes libraries that libsnark depends on, such as libff and libfqfft. Observe that libfqfft also includes a depends folder that depends on libff. To prevent library duplication or versioning issues, we have made the dependency requirements explicit at each level. Namely, when fetching libsnark’s dependencies, we will only fetch and build top-level submodules. We will not recursively fetch submodules. This system of enforcing dependencies will ensure CMake can reliably compile dependencies as native code to libsnark, and prevent hidden, shared-library dependency files from arising.

The CMake compilation scripts include optional flags that pass state about the current calling parent to respective dependencies. This prevents CMake from unnecessarily recompiling dependencies and resetting state. We have built this system to ensure code duplication and library duplication do not arise as part of a developer’s workflow.