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ENVIRONMENT-STRUCTURE.md

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Environment structure

As described in Features, the Holy Build Box environment consists of a bare-bones CentOS 7 system, on top of which a compiler toolchain and various libraries are installed.

Most of the compiler toolchain, e.g. gcc and g++, are installed with YUM. However, some software in CentOS 7 is too outdated for compiling modern applications, so we installed more recent versions of them from source.

  • Executable tools such as CMake are installed to /hbb.
  • Libraries such as OpenSSL are installed to the library variant directories, e.g. /hbb_exe.

The activation script inside each library variant directory sets various environment variables to ensure that whatever is inside that library variant directory is found first. For example, it prepends /hbb/bin and /hbb_<VARIANT NAME>/bin to PATH.

The activation script sets the following environment variables:

  • PATH
  • C_INCLUDE_PATH
  • CPLUS_INCLUDE_PATH
  • LIBRARY_PATH
  • PKG_CONFIG_PATH
  • O3_ALLOWED
  • CFLAGS
  • CXXFLAGS
  • LDFLAGS

Some environment variables deserve special explanation:

  • O3_ALLOWED signals whether the variant is compatible with -O3. It is set to true or false. It is true for all variants except for the exe_gc_hardened variant.
  • CFLAGS, CXXFLAGS and LDFLAGS are meant for compiling binaries.
  • STATICLIB_CFLAGS and STATICLIB_CXXFLAGS are meant for compiling static libraries. When compiling static libraries, you should set CFLAGS and CXXFLAGS to equal these variables.
  • SHLIB_CFLAGS, SHLIB_CXXFLAGS and SHLIB_LDFLAGS are meant for compiling shared libraries. When compiling shared libraries, you should set CFLAGS, CXXFLAGS and LDFLAGS to equal these variables.

You can inspect the environment variables by starting a bash shell and sourcing one of the activation scripts:

$ docker run -t -i --rm ghcr.io/phusion/holy-build-box/hbb-64 bash

container$ source /hbb_exe/activate
Holy build box activated
Prefix: /hbb_exe
CFLAGS: -O2 -fvisibility=hidden -I/hbb_exe/include
LDFLAGS: -L/hbb_exe -static-libstdc++
STATICLIB_CFLAGS: -O2 -fvisibility=hidden -I/hbb_exe/include
SHLIB_CFLAGS: -O2 -fvisibility=hidden -I/hbb_exe/include
SHLIB_LDFLAGS: -L/hbb_exe

container$ echo $CFLAGS
-O2 -fvisibility=hidden -I/hbb_exe/include