--- wikisrc/pkgsrc/gcc.mdwn 2017/11/26 01:07:36 1.1 +++ wikisrc/pkgsrc/gcc.mdwn 2017/11/26 01:28:44 1.3 @@ -1,8 +1,6 @@ -Using gcc in pkgsrc - On many systems pkgsrc supports, gcc is the standard compiler. In general, different versions of each OS have different gcc versions, -and some packages require newer GCC versions, in order to support +and some packages require newer gcc versions, in order to support newer language standards (e.g. c++11, written in the style of USE_LANGUAGES), or because older versions don't work (infrequently). @@ -20,7 +18,7 @@ build gcc versions (typically newer vers in a compiler within ${PREFIX}, e.g. /usr/pkg/gcc6/bin/gcc. This compiler can then be used to compile other packages. -Issues with using base system gcc are typically that it is too old, +The Issue with using base system gcc is typically that it is too old, such as gcc 4.5 with NetBSD 6, which cannot compile c++11. Issues when using pkgsrc gcc are that @@ -45,33 +43,42 @@ This section attempts to gather all the - The set of packages that are needed when building a bootstrap compiler should be minimized. - - All packages that use C++ should be built with the same compiler version. - - All packages that use C should have final linking with the highest version used in any included library. + - All packages that use C++ should be built with the same compiler + version. Because these in the general case may include C, the + version used for C++ must be at least as new as the version used + for any used C package. + - pkgsrc should avoid building gcc unless it is more or less necessary to build packges. (As an example, if the base system gcc can build c99 but not c++11, building a c99-only program should not trigger building a gcc version adequate for c++11.) - - The compiler selection logic should work on NetBSD 6, and in-use - (including LTS) GNU/Linux systems. It is desirable for this logic - to work on NetBSD 5. + - The compiler selection logic should work on NetBSD 6 and newer, + and other systems currently supported by pkgsrc, including in-use + LTS GNU/Linux systems. It should work on systems that default to + clang, when set to use GCC, at least as well as the current + scheme. It is desirable for this logic to work on NetBSD 5. - The compiler selection logic should be understandable and not brittle. ## Design The above requirements could in theory be satisfied in many ways, but -most of them are too complicated. +most of them are too complicated. We present a design that aims to be +sound while mimimizing complexity. - Packages declare what languages they need, with c++, c++11, and - c++14 being expressed differently. + c++14 being expressed differently. (This is exactly current + practice and just noted for completeness.) - The package-settable variable GCC_REQD will be used only when a compiler that generally can compile the declared language version - is insufficient. These cases are expected to be relatively rare. + is insufficient. These cases are expected to be relatively rare; + an example is firefox that is in c++ (but not c+11) and needs gcc + 4.9. - A user-settable variable PKGSRC_GCC_VERSION will declare the version of gcc to be used for C programs, with an OS- and @@ -95,8 +102,8 @@ most of them are too complicated. package building will fail. We call the resulting PKGSRC_GCC_VERSION or PKGSRC_GXX_VERSION the chosen version. - - When building a program using C or C++, the chosen version is not - provided by the base system, and the chosen version is not + - When building a program using C or C++, if the chosen version is + not provided by the base system, and the chosen version is not installed via pkgsrc, then it (and its dependencies) will be built from pkgsrc in a special bootstrap mode. When building in bootstrap mode, the version selection logic is ignored and the @@ -121,6 +128,9 @@ most of them are too complicated. approach is possible inconsistency with gcc's dependencies being built with the base compiler and used later. + - We hope that the chosen version can be built using the base system + version, and hope to avoid multi-stage bootstrapping. + - We expect that any program containing C++ will undergo final linking with a C++ compiler. This is not a change from the current situation. @@ -141,24 +151,32 @@ exist. \todo: Discuss adjusting options to minimize dependencies, including gcc-inplace-math and nls. +### Differing GCC and GXX versions + +Perhaps it is a mistake to allow the chosen GCC and GXX versions to +differ. If we require them to be the same, then essentially all +systems with a base system compiler older than gcc 5 will have to +bootstrap the compiler. For now, we allow them to differ and will +permit the defaults to differ. + ### Default versions for various systems -Note that if any particular system (or bulk build), a newer gcc has to -be built, it does not hurt incrementally to have built it earlier. +Note that if for any particular system's set of installed packages (or +bulk build), a newer gcc has to be built, it does not hurt to have +built it earlier. When the base system is old (e.g., gcc 4.5 in NetBSD 6, or 4.1, in NetBSD 5), then it is clear that a newer version must be built. For these, PKGSRC_GXX_VERSION should default to a newish gcc, avoiding being so new as to cause building issues. Currently, gcc6 is probably a good choice. PKGSRC_GCC_VERSION should probably default to the -system version if it can build C99, or match PKGSRC_GXX_VERSION, if -the system version is too old. Perhaps gcc 4.5 would be used, but 4.1 -not used. \todo Discuss. +system version if it can build all C99 programs, or match +PKGSRC_GXX_VERSION, if the system version is too old. Perhaps gcc 4.5 +would be used, but 4.1 not used. \todo Discuss. When the base system is almost new enough, the decision about the default is more complicated. A key example is gcc 4.8, found in -NetBSD 7. Firefox requires gcc 4.9 (\todo because the c++11 support -in 4.8 is not quite good enough), and all programs using c++14 also +NetBSD 7. Firefox requires gcc 4.9, and all programs using c++14 also need a newer version. One options is to choose 4.8, resulting in firefox failing, as well as all c++14 programs. Another is to choose 4.9, but this makes little sense because c++14 programs will still @@ -173,6 +191,18 @@ used. By "new enough", we mean that alm to build with it, which implies that it supports (almost all) C++14 programs. Our current definiton of new enough is gcc 5. +### Limited mixed versions + +One approach would be to allow limited mixed versions, where +individual programs could force a specific version to be bootstrapped +and used, so that e.g. firefox could use 4.9 even though most programs +use 4.8, which is what happens now on NetBSD 7. This would rely on +being able to link c++ with 4.9 including some things built with 4.8 +(which is done presently). However, this approach would become +unsound with a library rather than an end program. We reject this as +too much complexity for avoiding building a newer compiler in limited +situations. + ### Fortran Fortran support is currently somewhat troubled.. It seems obvious to @@ -198,3 +228,7 @@ not worsened by the above design. \todo is the base system version if >= 4.5 (or 4.4?), and otherwise 6, and that PKGSRC_GXX_VERSION is the base system version if >= 5, and otherwise 6. + +### Later steps + + - Address fortran.