Hybrid Builds

A hybrid build of Haiku used to be a regular Haiku built with gcc 2, also including the versions of the system libraries built with gcc 4 (or vice versa), so that programs built with either compiler could be run. Package management extends that concept and makes it more modular. Since it assigns gcc 2 and gcc 4 different (packaging) architectures ("x86_gcc2" and "x86"), we can now speak of a primary architecture -- the one the system has been built for -- and a secondary architecture -- the one the additional set of system libraries has been built for. This also fits fine with the x86_64+x86 hybrid option we might see in the future.

Since the files for the secondary architecture will live in one or more separate packages we gain some flexibility. E.g. one could start out with a non-hybrid Haiku and install the packages for the secondary architecture later on, and remove them when no longer needed. In theory there's nothing preventing us from supporting multiple secondary architectures (e.g. x86_64+x86+x86_gcc2), though that might get somewhat confusing in practice.

The following sections list the requirements for the hybrid concept and the packages built for a secondary architecture.

General Requirements

1. Secondary architecture libraries and add-ons must live in respective "<secondary_arch>" subdirectory, where the runtime loader will only look when loading a secondary architecture executable.
2. Secondary architecture development libraries and headers must live in "<secondary_arch>" subdirectory, where only the secondary architecture compiler will look for them.
3. Secondary architecture executables must live in a "<secondary_arch>" subdirectory, which by default isn't in PATH. The executables can be symlinked to the primary architecture "bin" directory, using a symlink name that doesn't clash with the primary architecture executable's name (by appending to the name the secondary architecture name, e.g. "grep-x86"). If there isn't a corresponding package for the primary architecture, the executables may also live directly in the "bin" directory.
4. Application directories should live in a "<secondary_arch>" subdirectory, unless there isn't a corresponding package for the primary architecture.

Secondary Architecture Package Requirements

1. A secondary architecture package must not conflict with the corresponding primary architecture package, so both can be active at the same time and in the same installation location.
2. Packages that require a command ("cmd:...") and don't need it to be for a particular architecture shouldn't need to be concerned with the primary/secondary architecture issue. E.g. "cmd:grep" should provide them with a working grep.
3. Secondary architecture packages providing a command should generally provide both "cmd:<command>" and "cmd:<command>_<secondary_arch>" (e.g. "cmd:grep" and "cmd:grep_x86_gcc2"). The former makes 2. possible. The latter allows for packages to explicitly require the command for the secondary architecture (3. of the general requirements actually implies that provides item). The former should be omitted, when the behavior/output of the command is architecture dependent (e.g. in case of compilers etc.).
4. Secondary architecture packages providing a library must provide "lib:<library>_<secondary_arch>" (e.g. "lib:libncurses_x86").