Before making code changes, it is helpful to become familiar with Dory's build system, which is based on SCons.
Files SConstruct and src/SConscript
contain the build configuration. As shown
here, to build something, first
source the file bash_defs in the root of Dory's Git
repository. Then cd into the src directory or any directory beneath src
and use the build command to build a particular target. In general, to build
an executable you simply specify its name when invoking the build command.
For instance:
source bash_defs
cd src/dory
build dory # builds dory executable
build client/to_dory # builds command line client
build msg.o # compile source file msg.cc
build conf/conf.o # compile source file conf/conf.cc
If you are building on CentOS/RHEL 7, remember to build within a shell started
by scl enable devtoolset-8 bash, as detailed here.
All build results are in the out directory (relative to the root of the Git
repository). For instance, the built dory executable will be
out/debug/dory/dory. To build a release version of a target, use the
--release option with the build command. For instance,
build --release dory will build a release version of dory, which will be
out/release/dory/dory.
Source files ending in .test.cc are unit tests, which can be executed as
standalone executables. For instance, in the above example if we typed
build unix_dg_input_agent.test, this would build the unit test for Dory's
UNIX datagram input agent, which would then appear as executable file
out/debug/dory/unix_dg_input_agent.test. If you type
build --test unix_dg_input_agent.test, that will build the unit test and then
immediately execute it.
If you type build -c, that will remove all build artifacts by deleting the
out directory. For make users, this is the equivalent of make clean.
Alternatively, you can just type rm -fr out from the root of the Git
repository. If you wish to change any compiler or linker flags, look for the
section of code in the SConstruct file that looks roughly like this:
xerces_lib_deps = ['xerces-c']
ext_lib_deps = [
[r'^dory/dory\.test$', xerces_lib_deps],
[r'^dory/unix_dg_input_agent\.test$', xerces_lib_deps],
[r'^dory/stream_client_handler\.test$', xerces_lib_deps],
[r'^dory/conf/conf\.test$', xerces_lib_deps],
[r'^xml/.*', xerces_lib_deps],
[r'^dory/dory$', xerces_lib_deps]
]
env = Environment()
# As documented here:
#
# https://www.softwarecollections.org/en/scls/rhscl/devtoolset-8/
#
# gcc 8 is enabled on CentOS 7 by building in an environment set up by the
# following command:
#
# scl enable devtoolset-8 bash
#
# See if we are executing in this kind of environment. If so, we must inject
# our environment variables into the build environment so gcc 8 is used.
if 'X_SCLS' in os.environ and \
'devtoolset-8' in os.environ['X_SCLS'].split(' '):
env.Append(ENV=os.environ)
prog_libs = {'pthread', 'dl', 'rt', 'z'}
env.Append(CFLAGS=['-Wwrite-strings'],
CCFLAGS=['-Wall', '-Wextra', '-Werror', '-Wformat=2', '-Winit-self',
'-Wunused-parameter', '-Wshadow', '-Wpointer-arith',
'-Wcast-align', '-Wlogical-op', '-Wno-nonnull-compare'],
CPPDEFINES=[('SRC_ROOT', '\'"' + src.abspath + '"\'')],
CPPPATH=[src, tclap, gtestincdir],
CXXFLAGS=['-std=c++2a', '-Wold-style-cast', '-Wno-noexcept-type'],
DEP_SUFFIXES=['.cc', '.cpp', '.c', '.cxx', '.c++', '.C'],
PROG_LIBS=[lib for lib in prog_libs],
TESTSUFFIX='.test',
EXT_LIB_DEPS=ext_lib_deps)
def set_debug_options():
# Note: If you specify -fsanitize=address, you must also specify
# -fno-omit-frame-pointer and be sure libasan is installed (RPM package
# libasan on RHEL, Fedora, and CentOS).
env.AppendUnique(CCFLAGS=['-g3', '-ggdb', '-fno-omit-frame-pointer',
'-fvisibility=hidden'])
env.AppendUnique(CXXFLAGS=['-D_GLIBCXX_DEBUG',
'-D_GLIBCXX_DEBUG_PEDANTIC',
'-DTRACK_FILE_DESCRIPTORS'])
env.AppendUnique(LINKFLAGS=['-rdynamic'])
if GetOption('asan') == 'yes':
env.AppendUnique(CCFLAGS=['-fsanitize=address'])
env.AppendUnique(LINKFLAGS=['-fsanitize=address'])
def set_release_options():
# TODO: Enable link-time optimizations.
env.AppendUnique(CCFLAGS=['-O2', '-DNDEBUG', '-Wno-unused',
'-Wno-unused-parameter', '-fvisibility=hidden'])
env.AppendUnique(LINKFLAGS=['-rdynamic'])Note that SCons build files are actually Python scripts, so you can add
arbitrary Python code. Adding, removing or renaming source files does not
require any changes to the build scripts, since they are written to figure out
the dependencies on their own. If you want to build all targets (or a
substantial subset of all targets) with a single command, you can execute the
build_all script in the root of the Git repository. For
instance, build_all run_tests will build and run all unit tests. Type
build_all --help for a full description of the command line options.
Eventually it would be nice to eliminate the build_all script and integrate
its functionality directly into the SCons configuration.
As shown above, if you use the build command to build an individual binary,
it will create a debug version by default if --release is not specified.
Likewise, if you do not specify --mode=release when running the build_all
script, debug versions of binaries will be built by default. As documented
here, the pkg command may be used
for building an RPM package. By default, pkg builds a release version of
Dory. To build a debug version, specify --debug.
GCC provides support for AddressSanitizer, a useful debugging tool. This is enabled by default in debug builds. When running Dory with the address sanitizer, you may notice that it uses a large amount of virtual memory (often multiple terabytes). This is expected behavior. After running Dory for a while with the address sanitizer, it may exit with the following error message:
ERROR: Failed to mmap
If this causes problems, you can build Dory with the address sanitizer disabled. When building Dory directly, as described here, you can disable the address sanitizer as follows:
build --asan=no dory
Likewise, you can invoke build_all as follows:
./build_all --asan=no
When building an RPM package (as described here), a debug version with the address sanitizer disabled may be created as follows:
./pkg --debug --asan no rpm
or
./pkg --debug --asan no rpm_noconfig
Another thing to keep in mind about the address sanitizer's behavior is that it
causes operator new to return nullptr on allocation failure in cases where
the C++ standard dictates that std::bad_alloc should be thrown. This can
cause out of memory conditions to result in segmentation faults due to null
pointer dereferences. See
this issue for details.
Regardless of how you build dory (via the build command, the build_all
script, or the pkg script), the address sanitizer is always disabled in
release builds, regardless of any command line options that disable or enable
the address sanitizer.
The GNU C++ library provides a debug mode which implements various assertion checks for STL containers. Dory makes use of this in its debug build. A word of caution is therefore necessary. Suppose you have the following piece of code:
/* Do something interesting to an array of int values. 'begin' points to the
beginning of the array and 'end' points one position past the last element.
'begin' and 'end' will be equal in the case of an empty input. */
void DoSomethingToIntArray(int *begin, int *end) {
assert(begin || (end == begin));
assert(end >= begin);
// do something interesting ...
}
void foo(std::vector<int> &v) {
DoSomethingToIntArray(&v[0], &v[v.size()]);
}The above code is totally legitimate C++. However, the expression
&v[v.size()] will cause an out of range vector index to be reported when
running with debug mode enabled. In fact, the expression &v[0] is enough to
cause an error to be reported in the case where v is empty. Therefore the
code needs to be written a bit differently to avoid spurious errors in debug
builds. For instance, one might instead implement foo() like this:
void foo(std::vector<int> &v) {
if (!v.empty()) {
DoSomethingToIntArray(&v[0], &v[0] + v.size());
}
}Although this is a bit less elegant than the previous implementation, the
benefits of tools such as debug mode can be great when tracking down problems.
Therefore please avoid code such as the first version of foo() when making
changes to Dory.
Information on contributing to Dory is provided here.
dev_info.md: Copyright 2019 Dave Peterson (dave@dspeterson.com) Copyright 2014 if(we), Inc.
dev_info.md is licensed under a Creative Commons Attribution-ShareAlike 4.0 International License.
You should have received a copy of the license along with this work. If not, see http://creativecommons.org/licenses/by-sa/4.0/.