--- wikisrc/pkgsrc/gcc.mdwn 2017/11/26 15:37:02 1.4 +++ wikisrc/pkgsrc/gcc.mdwn 2018/01/01 23:27:13 1.11 @@ -18,11 +18,15 @@ 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. -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. +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. Another +example is gcc 4.8 with NetBSD 7. While this can compile most c++11 +programs, it cannot be used for firefox or glibmm (and therefore any +package that links against glibmm). Issues when using pkgsrc gcc are that + - on some platforms, pkgsrc gcc does not build and work - it must be bootstrapped, requiring compiling a number of packages with the system compiler - C++ packages that are linked together should be built with the @@ -62,6 +66,9 @@ This section attempts to gather all the 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. + - All systems should work at least as well as they do before + implementation of new compiler selection logic. + - The compiler selection logic should be understandable and not brittle. ## Design @@ -81,12 +88,19 @@ sound while mimimizing complexity. 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 - version--specific default. + version of gcc to be used for C programs, with an OS-, + version- and architeture- specific default. - - A user-settable variable PKGSRC_GXX_VERSION will declare the version of gcc to - be used for all C++ programs, again with an OS- and - version-specific default. It must be at least PKGSRC_GCC_VERSION. + - A user-settable variable PKGSRC_GXX_VERSION will declare the + version of gcc to be used for all C++ programs, again with an OS-, + version- and architeture-specific default. It must be at least + PKGSRC_GCC_VERSION. + + - If PKGSRC_GCC_VERSION and PKGSRC_GXX_VERSION are not set, the + system will behave much as before. As a possible exception, + builds may still fail if the required version is greater than the + base system version. So far the only known reason to avoid + setting these variable is if pkgsrc gcc cannot be built. - Each of c99, c++, c++11, and c++14 will be associated with a minimum gcc version, such that almost all programs declaring that @@ -128,6 +142,13 @@ sound while mimimizing complexity. approach is possible inconsistency with gcc's dependencies being built with the base compiler and used later. + As an alternative, we store lists of bootstrap packages in a + variable, because it will vary with OS and version, and with + PREFER_PKGSRC settings. + + As a third alternative, we pass a GCC_BOOTSTRAPPING variable + recursively. This is easier but less consistent. + - We hope that the chosen version can be built using the base system version, and hope to avoid multi-stage bootstrapping. @@ -137,7 +158,7 @@ sound while mimimizing complexity. ## Remaining issues -### gcc dependencies +### gcc dependencies introduction Because gcc can have dependencies, there could be packages built with the system compiler that are then later used with the chosen version. @@ -145,11 +166,56 @@ For now, we defer worrying about these p will be less serious than the current situation where all c++11 programs fail to build on NetBSD 6). +\todo: Perhaps change gcc 4.8 and 4.9 to enable gcc-inplace-math by +default. Perhaps decide that if we want to build gcc, we want to +build 5 or 6, and 4.9 is no longer of interest as a bootstrap target. + \todo: Analyze what build-time and install-time dependencies actually -exist. +exist. Include old GNU/Linux in this analysis. + +\todo: Consider if dropping nls would help. (On NetBSD, it seems that +base system libraries are used, so it would not help.) + +\todo: Consider failing if optins that we want one way are another, +when bootstrapping. + +### managing gcc dependencies + +There are multiple paths forward. + +\todo Choose one. Straw proposal is "Don't worry" and recursive +variable for the initial implementation. + +#### Separate prefix + +Build compilers in a separate prefix, or a subprefix, so that the +compiler and the packages needed to build it will not be used by any +normal packages. This completely avoids the issue of building a +package one way in bootstrap and another not in bootstrap, at the cost +of two builds and writing the separate-prefix code. + +#### Don't worry + +Don't worry that packages used to bootstrap the needed compiler are +compiled with an older compiler. Don't worry that they might be +different depending on build order. If we have an actual problem, +deal with it. This requires choosing an approach to omit compiler +selection logic when building the compiler: + +##### Mark bootstrap packages + +Mark packages used to build gcc as PKGSRC_GCC_BOOTSTRAP=yes. +Conditionalize this on OPSYS if necessary. Don't force the compiler +if this is set. -\todo: Discuss adjusting options to minimize dependencies, including -gcc-inplace-math and nls. +Alternatively, manage a per-OS list of packages in a central mk file. + +##### Pass a recursive variable + +As above, but set PKGSRC_GCC_BOOTSTRAP=yes in the evniroment of the +call to build the compiler, so that all dependencies inherit +permission to skip compiler selection logic. (Alternatively, use some +other mechanism such as passing a make variable explicitly.) ### Differing GCC and GXX versions @@ -159,6 +225,27 @@ systems with a base system compiler olde bootstrap the compiler. For now, we allow them to differ and will permit the defaults to differ. +### gcc versions and number of buildable packages + +A gcc version that is too old will not build a number of packages. +Anything older than 4.8 fails for c++11. 4.8 fails on some c++11 +packages, such as firefox and glibmm. + +A version that is too new also fails to build packages. Jason Bacon +posted counts to tech-pkg indicate that 5 is close to 4.8 in the +number of packages built, and that moving to 6 causes hundreds of +additional failures. (Keep in mind that currently, building with 4.8 +will build 4.9 for firefox, but in the future will not.) + + www/pkgsrc/packages/sharedapps/pkg-2017Q3/RHEL6-gcc48/All 16461 + www/pkgsrc/packages/sharedapps/pkg-2017Q3/RHEL6-gcc6/All 15849 + + www/pkgsrc/packages/sharedapps/pkg-2017Q3/RHEL7-gcc48/All 16414 + www/pkgsrc/packages/sharedapps/pkg-2017Q3/RHEL7-gcc5/All 16338 + +Therefore, the current answer to "What is the best version to use" is +5. + ### Default versions for various systems Note that if for any particular system's set of installed packages (or @@ -168,12 +255,10 @@ 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, gcc5 is probably -a good choice, with gcc6 compiling significantly but not vastly fewer -packages. PKGSRC_GCC_VERSION should probably default to the 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. +being so new as to cause building issues. PKGSRC_GCC_VERSION should +probably default to the 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 @@ -182,15 +267,16 @@ need a newer version. One options is to 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 fail, and the general rule of moving to the most recent -generally-acceptable version applies, which currently leads to gcc6. +generally-acceptable version applies, which currently leads to gcc5. This is in effect a declaration that "almost new enough" does not count as new enough. Thus the plan for NetBSD 7 is to set PKGSRC_GCC_VERSION to 4.8 and PKGSRC_GXX_VERSION to 5. When the base system is new enough, e.g. gcc 5, 6 or 7 it should simply be used. By "new enough", we mean that almost no programs in -pkgsrc fail to build with it, which implies that it supports (almost -all) C++14 programs. Our current definiton of new enough is gcc 5. +pkgsrc fail to build with it (because it is too old), which implies +that it supports (almost all) C++14 programs. Our current definiton +of new enough is gcc 5. ### Limited mixed versions @@ -209,10 +295,30 @@ situations. Fortran support is currently somewhat troubled.. It seems obvious to extend to PGKSRC_GFORTRAN_VERSION, and have that match PKGSRC_GCC_VERSION or PKGSRC_GXX_VERSION, but the Fortran situation is -not worsened by the above design. \todo Discuss. +not worsened by the above design. + +When building a gcc version, we get gfortran. Perhaps, because of +fortran, we should require a single version, vs a C and a C++ version. + +\todo Discuss. + +### C++ libraries used by C programs + +The choice of one version for C++ and one for C (e.g. 5, 4.8 on +netbsd-7) breaks down if a C program links against a library that is +written in C++ but provides a C API, because we still need the C++ +version's stdlib. + +\todo Define a variable for such packages to have in their buildlink3, +which will not add c++ to USE_LANGUAGES but will force +PKGSRC_GXX_VERSION to be used. Or decide that this is a good reason +to really just have one compiler version. ## Path forward +(This assumes per-package marking of bootstrap packages, but is +reasonably obviously extended to the other schemes.) + - Modify all gcc packages to have minimal dependencies, and to add PKGSRC_GCC_BOOTSTRAP. @@ -222,14 +328,16 @@ not worsened by the above design. \todo - Modify the compiler selection logic for LANGUAGES= to fail if PKGSRC_GCC_VERSION/PKGSRC_GXX_VERSION is not new enough. - - Modify the compiler selection logic for GCC_REQD to fail if the - version of GCC/GXX is not new enough. + - Modify the compiler selection logic for GCC_REQD to fail if + PKGSRC_GCC_VERSION/PKGSRC_GXX_VERSION is not new enough. - Decide on defaults. The straw proposal is that PKGSRC_GCC_VERSION - is the base system version if >= 4.5 (or 4.4?), and otherwise 6, + is the base system version if >= 4.5 (or 4.4?), and otherwise 5, and that PKGSRC_GXX_VERSION is the base system version if >= 5, and - otherwise 6. + otherwise 5. Implement these in platform.mk as they are tested. ### Later steps - - Address fortran. + - Address fortran. Probably add PKGSRC_GFORTRAN_VERSION, after + determining how Fortran, C and C++ interact with library ABI + compatibility.