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RPM Macros for Build Flags

Summary

Create a corresponding macro for each compiler flag in the redhat-rpm-config macro file and create "extra flag" macros to make it easier for packages to add and remove compiler flags.

Owner

Current status

Detailed Description

The macros file in the redhat-rpm-config package contains a list of default compiler flags for packages to use when compiling C, C++, and Fortran packages. There is currently no standard way to remove or add to the set of default flags. Most packages use a combination of echo and sed to remove unwanted flags or add new ones. Some examples:

   compiler-rt: global optflags %(echo %{optflags} -D_DEFAULT_SOURCE)
   julia:       %global optflags %(echo %{optflags} | sed 's/-Wp,-D_GLIBCXX_ASSERTIONS //')

This change will add new macros which will make it easier for packages to add and remove their own compiler flags. This strategy is already used to some extent with feature macros like %{_lto_cflags}, %{_hardening_cflags}, etc, but these new macros will give packagers even more fine-grained control over the options.

The proposed macros for adding new flags are:

   %_pkg_extra_cflags
   %_pkg_extra_cxxflags
   %_pkg_extra_fflags
   %_pkg_extra_ldflags

These will be added to %{build_cflags}, %{build_cxxflags}, %{build_fflags}, and %{build_ldflags} respectively to allow packges to add their own flags to the default list: e.g.

   %build_cflags %{optflags} %{_pkg_extra_cflags}

The proposed new macros to represent existing flags are:

   %_flag_fstack_protector_strong     -fstack-protector-strong
   %_flag_z_now                       -Wl,-z,now
   %_flag_z_defs                      -Wl,-z,defs
   %_flag_flto_auto                   -flto=auto
   %_flag_ffat_lto_objects            -ffat-lto-objects
   %_flag_o                           -O2
   %_flag_f_exceptions                -fexceptions
   %_flag_g                           -g
   %_flag_grecord_gcc_switches        -grecord-gcc-switches
   %_flag_pipe                        -pipe
   %_flag_wall                        -Wall
   %_flag_werror_format_security      -Werror=format-security
   %_flag_fortify_source              -Wp,-D_FORTIFY_SOURCE=2
   %_flag_glibcxx_assertions          -Wp,-D_GLIBCXX_ASSERTIONS
   %_flag_asynchronous_unwind_tables  -fasynchronous-unwind-tables
   %_flag_fstack_clash_protection     -fstack-clash-protection
   %_flag_fcf_protection              -fcf-protection
   %_flag_mbranch_protection_standard -mbranch-protection=standard

With these new macros, the examples from above could be re-written as:

   compiler-rt: %global _pkg_extra_cflags -D_DEFAULT_SOURCE
   julia:       %global _flag_glibcxx_assertions %{nil}

For more details see the Prototype Implementation.

In addition to adding these new macros, the packaging guidelines will be updated to require that all new flags added to redhat-rpm-config have their own RPM macro.

Feedback

Benefit to Fedora

  • It will provide a standard way to disable existing compiler flags or enable new ones that is more simple and robust than the existing echo + sed solution.
  • It will make it easier to determine which packages disable or add compiler flags by doing a simple grep of the spec files.
  • It will make it easier for toolchain developers to experiment with adding new flags to the distribution as this can be done with a simple macro definition instead of patching redhat-rpm-config.

Scope

  • Proposal owners:
    • Proposal owners will update the redhat-rpm-config package and add the new macros.
    • Proposal owners will test the changes to ensure that the correct flags are still being used.
  • Other developers:
    • Other developers may, but are not required to, update their packages to use the new macros.
  • Policies and guidelines:
    • The Fedora packaging policy will be updated to require that new flags added to redhat-rpm-config come with their own RPM macro.
  • Trademark approval: N/A (not needed for this Change)
  • Alignment with Objectives:

Upgrade/compatibility impact

None.

How To Test

  • This can be tested by inspecting the value of the %{build_cflags}, %{build_cxxflags}, %{build_fflags}, and %{build_ldflags} and ensuring they are the same before and after the change.
  • This can be tested by modifying some of the new macros in a spec file and ensuring that the changes appear in the appropriate macro mentioned above.

User Experience

This is a change for developers and will have no impact to the user experience.

Dependencies

None.

Contingency Plan

  • Contingency mechanism: (What to do? Who will do it?) Change owner will revert the update to redhat-rpm-config.
  • Contingency deadline: Mass Rebuild
  • Blocks release? N/A (not a System Wide Change), No

Documentation

None.

Release Notes

None.