Diff for /wikisrc/pkgsrc/gcc.mdwn between versions 1.5 and 1.12

version 1.5, 2017/11/26 15:43:57 version 1.12, 2018/01/04 20:37:58
Line 10  be converted into historical design rati Line 10  be converted into historical design rati
 freely takes content from extensive mailinglist discussions, and  freely takes content from extensive mailinglist discussions, and
 attempts to follow the rough consensus that has emerged.  attempts to follow the rough consensus that has emerged.
   
 ## Base system gcc vs pkgsrc gcc  # Base system gcc vs pkgsrc gcc
   
 Systems using gcc (e.g. NetBSD) have a compiler as /usr/bin/gcc, and  Systems using gcc (e.g. NetBSD) have a compiler as /usr/bin/gcc, and
 this is usable by pkgsrc without any bootstrapping activity.  One can  this is usable by pkgsrc without any bootstrapping activity.  One can
Line 18  build gcc versions (typically newer vers Line 18  build gcc versions (typically newer vers
 in a compiler within ${PREFIX}, e.g. /usr/pkg/gcc6/bin/gcc.  This  in a compiler within ${PREFIX}, e.g. /usr/pkg/gcc6/bin/gcc.  This
 compiler can then be used to compile other packages.  compiler can then be used to compile other packages.
   
 The Issue with using base system gcc is 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.  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  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    - it must be bootstrapped, requiring compiling a number of packages
     with the system compiler      with the system compiler
   - C++ packages that are linked together should be built with the    - C++ packages that are linked together should be built with the
Line 32  Issues when using pkgsrc gcc are that Line 36  Issues when using pkgsrc gcc are that
     should be linked with the higher version because the support      should be linked with the higher version because the support
     library is backwards compatible but not forward compatible.      library is backwards compatible but not forward compatible.
   
 ## Specific constraints and requirements  # Specific constraints and requirements
   
 This section attempts to gather all the requirements.  This section attempts to gather all the requirements.
   
Line 62  This section attempts to gather all the  Line 66  This section attempts to gather all the 
     clang, when set to use GCC, at least as well as the current      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.      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.    - The compiler selection logic should be understandable and not brittle.
   
 ## Design  # Design
   
 The above requirements could in theory be satisfied in many ways, but  The above requirements could in theory be satisfied in many ways, but
 most of them are too complicated.  We present a design that aims to be  most of them are too complicated.  We present a design that aims to be
Line 81  sound while mimimizing complexity. Line 88  sound while mimimizing complexity.
     4.9.      4.9.
   
   - A user-settable variable PKGSRC_GCC_VERSION will declare the    - A user-settable variable PKGSRC_GCC_VERSION will declare the
     version of gcc to be used for C programs, with an OS- and      version of gcc to be used for C programs, with an OS-,
     version--specific default.      version- and architeture- specific default.
   
   - A user-settable variable PKGSRC_GXX_VERSION will declare the version of gcc to    - A user-settable variable PKGSRC_GXX_VERSION will declare the
     be used for all C++ programs, again with an OS- and      version of gcc to be used for all C++ programs, again with an OS-,
     version-specific default.  It must be at least PKGSRC_GCC_VERSION.      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    - Each of c99, c++, c++11, and c++14 will be associated with a
     minimum gcc version, such that almost all programs declaring that      minimum gcc version, such that almost all programs declaring that
Line 128  sound while mimimizing complexity. Line 142  sound while mimimizing complexity.
     approach is possible inconsistency with gcc's dependencies being      approach is possible inconsistency with gcc's dependencies being
     built with the base compiler and used later.      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    - We hope that the chosen version can be built using the base system
     version, and hope to avoid multi-stage bootstrapping.      version, and hope to avoid multi-stage bootstrapping.
   
Line 135  sound while mimimizing complexity. Line 156  sound while mimimizing complexity.
     linking with a C++ compiler.  This is not a change from the      linking with a C++ compiler.  This is not a change from the
     current situation.      current situation.
   
 ## Remaining issues  # Remaining issues
   
 ### gcc dependencies  ## gcc dependencies introduction
   
 Because gcc can have dependencies, there could be packages built with  Because gcc can have dependencies, there could be packages built with
 the system compiler that are then later used with the chosen version.  the system compiler that are then later used with the chosen version.
Line 145  For now, we defer worrying about these p Line 166  For now, we defer worrying about these p
 will be less serious than the current situation where all c++11  will be less serious than the current situation where all c++11
 programs fail to build on NetBSD 6).  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  \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.
   
 \todo: Discuss adjusting options to minimize dependencies, including  ### Separate prefix
 gcc-inplace-math and nls.  
   
 ### Differing GCC and GXX versions  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.
   
   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
   
 Perhaps it is a mistake to allow the chosen GCC and GXX versions to  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  differ.  If we require them to be the same, then essentially all
Line 159  systems with a base system compiler olde Line 225  systems with a base system compiler olde
 bootstrap the compiler.  For now, we allow them to differ and will  bootstrap the compiler.  For now, we allow them to differ and will
 permit the defaults to differ.  permit the defaults to differ.
   
 ### Default versions for various systems  ## 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  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  bulk build), a newer gcc has to be built, it does not hurt to have
Line 168  built it earlier. Line 255  built it earlier.
 When the base system is old (e.g., gcc 4.5 in NetBSD 6, or 4.1, in  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  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  these, PKGSRC_GXX_VERSION should default to a newish gcc, avoiding
 being so new as to cause building issues.  Currently, gcc5 is probably  being so new as to cause building issues.  PKGSRC_GCC_VERSION should
 a good choice, with gcc6 compiling significantly but not vastly fewer  probably default to the system version if it can build all C99
 packages.  PKGSRC_GCC_VERSION should probably default to the system  programs, or match PKGSRC_GXX_VERSION, if the system version is too
 version if it can build all C99 programs, or match PKGSRC_GXX_VERSION,  old.  Perhaps gcc 4.5 would be used, but 4.1 not used.  \todo Discuss.
 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  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  default is more complicated.  A key example is gcc 4.8, found in
Line 182  need a newer version.  One options is to Line 267  need a newer version.  One options is to
 firefox failing, as well as all c++14 programs.  Another is to choose  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  4.9, but this makes little sense because c++14 programs will still
 fail, and the general rule of moving to the most recent  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  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  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.  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  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  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  pkgsrc fail to build with it (because it is too old), which implies
 all) C++14 programs.  Our current definiton of new enough is gcc 5.  that it supports (almost all) C++14 programs.  Our current definiton
   of new enough is gcc 5.
   
 ### Limited mixed versions  ## Limited mixed versions
   
 One approach would be to allow limited mixed versions, where  One approach would be to allow limited mixed versions, where
 individual programs could force a specific version to be bootstrapped  individual programs could force a specific version to be bootstrapped
Line 204  unsound with a library rather than an en Line 290  unsound with a library rather than an en
 too much complexity for avoiding building a newer compiler in limited  too much complexity for avoiding building a newer compiler in limited
 situations.  situations.
   
 ### Fortran  ## Fortran
   
 Fortran support is currently somewhat troubled..  It seems obvious to  Fortran support is currently somewhat troubled..  It seems obvious to
 extend to PGKSRC_GFORTRAN_VERSION, and have that match  extend to PGKSRC_GFORTRAN_VERSION, and have that match
 PKGSRC_GCC_VERSION or PKGSRC_GXX_VERSION, but the Fortran situation is  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.
   
 ## Path forward  \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   - Modify all gcc packages to have minimal dependencies, and to add
    PKGSRC_GCC_BOOTSTRAP.     PKGSRC_GCC_BOOTSTRAP.
Line 222  not worsened by the above design.  \todo Line 328  not worsened by the above design.  \todo
  - Modify the compiler selection logic for LANGUAGES= to fail if   - Modify the compiler selection logic for LANGUAGES= to fail if
    PKGSRC_GCC_VERSION/PKGSRC_GXX_VERSION is not new enough.     PKGSRC_GCC_VERSION/PKGSRC_GXX_VERSION is not new enough.
   
  - Modify the compiler selection logic for GCC_REQD to fail if the   - Modify the compiler selection logic for GCC_REQD to fail if
    version of GCC/GXX is not new enough.     PKGSRC_GCC_VERSION/PKGSRC_GXX_VERSION is not new enough.
   
  - Decide on defaults.  The straw proposal is that PKGSRC_GCC_VERSION   - Decide on defaults.  The straw proposal is that PKGSRC_GCC_VERSION
    is the base system version if >= 4.5 (or 4.4?), and otherwise 5,     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     and that PKGSRC_GXX_VERSION is the base system version if >= 5, and
    otherwise 5.     otherwise 5.  Implement these in platform.mk as they are tested.
   
   ## Later steps
   
    - Address fortran.  Probably add PKGSRC_GFORTRAN_VERSION, after
      determining how Fortran, C and C++ interact with library ABI
      compatibility.
   
   # Data
   
   This section has data points that are relevant to the discussion.
   
   ## amd64/i386
   
   It is believed that pkgsrc gcc generally builds on these systems.
   gcc6 builds on netbsd-5/i386.
   
 ### Later steps  ## macppc
   
  - Address fortran.  On macppc, [lang/gcc5 fails on netsbd-6 and netbsd-7, but succeeds on
   netbsd-8](https://mail-index.netbsd.org/tech-pkg/2018/01/03/msg019260.html).

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