3.4 KiB
Sandboxing PFFFT library
Build System: CMake
OS: Linux
Check out the PFFFT library & CMake set up
git submodule add https://bitbucket.org/jpommier/pffft.git
mkdir -p build && cd build
cmake .. -G Ninja -DPFFFT_ROOT_DIR=$PWD
ninja
For testing:
cd build, then ./pffft_sandboxed
For debug:
display custom info with
./pffft_sandboxed --logtostderr
About the project
PFFFT library is concerned with 1D Fast-Fourier Transformations finding a
compromise between accuracy and speed. It deals with real and complex
vectors, both cases being illustrated in the testing part (main_pffft.c
for initially and original version, main_pffft_sandboxed.cc for our
currently implemented sandboxed version).
The original files can be found at: https://bitbucket.org/jpommier/pffft/src.
The purpose of sandboxing is to limit the permissions and capabilities of
library’s methods, in order to secure the usage of them.
After obtaining the sandbox, the functions will be called through an
Sandbox API (being called api in the current test) and so, the
operations, system calls or namspaces access may be controlled.
From both pffft.h and fftpack.h headers, useful methods are added to
sapi library builded with CMake. There is also a need to link math library
as the transformations made require mathematical operators.
Regarding the testing of the methods, one main is doing this job by
iterating through a set of values, that represents the accuracy of
transformations and print the speed for each value and type of
transformation. More specifically, the input length is the target for
accuracy (named as N) and it stands for the number of data points from
the series that calculate the result of transformation. It is also
important to mention that the cplx variable stands for a boolean value
that tells the type of transformation (0 for REAL and 1 for COMPLEX) and
it is taken into account while testing.
In the end, the performance of PFFFT library it is outlined by the output.
CMake observations resume:
- linking pffft and fftpack (which contains necessary functions for pffft)
- set math library
Sandboxed main observations resume:
- containing two testing parts (fft / pffft benchmarks)
- showing the performance of the transformations implies testing them through various FFT dimenstions. Variable N, the input length, will take specific values meaning the number of points to which it is set the calculus (more details of mathematical purpose of N - https://en.wikipedia.org/wiki/Cooley%E2%80%93Tukey_FFT_algorithm).
- output shows speed depending on the input length
Bugs history
1. [Solved] pffft benchmark bug: "Sandbox not active"
N = 64, status OK, pffft_transform generates error
N > 64, status not OK
Problem on initialising sapi::StatusOr<PFFFT_Setup *> s; the memory that stays
for s is not the same with the address passed in pffft_transform function.
(sapi::v::GenericPtr - to be changed)
Temporary solution: change the generated files to accept
uintptr_t instead of PFFFT_Setup
Solution: using "sapi::v::RemotePtr" instead of "sapi::v::GenericPtr"
to access the memory of object s
2. [Unresolved] compiling bug: "No space left on device"
The building process creates some `embed` files that use lots of
memory, trying to write them on /tmp.
Temporary solution: clean /tmp directory by `sudo rm -rf /tmp/*`.