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== Current status == | == Current status == | ||
* Targeted release: [[Releases/ | * Targeted release: [[Releases/34| Fedora 34 ]] | ||
* Last updated: <!-- this is an automatic macro — you don't need to change this line --> {{REVISIONYEAR}}-{{REVISIONMONTH}}-{{REVISIONDAY2}} | * Last updated: <!-- this is an automatic macro — you don't need to change this line --> {{REVISIONYEAR}}-{{REVISIONMONTH}}-{{REVISIONDAY2}} | ||
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* Tracker bug: | * Tracker bug: [https://bugzilla.redhat.com/show_bug.cgi?id=1790581 #1790581] | ||
* Release notes tracker: | * Release notes tracker: [https://pagure.io/fedora-docs/release-notes/issue/431 #431] | ||
== Detailed Description == | == Detailed Description == | ||
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<!-- Expand on the summary, if appropriate. A couple sentences suffices to explain the goal, but the more details you can provide the better. --> | <!-- Expand on the summary, if appropriate. A couple sentences suffices to explain the goal, but the more details you can provide the better. --> | ||
The gcc package currently installs symlinks to /usr/bin/cc and /usr/bin/c++ which point to /usr/bin/gcc and /usr/bin/g++ respectively. For this change, the gcc package will be modified so that update-alternatives creates these symlinks. | The gcc package currently installs symlinks to /usr/bin/cc and /usr/bin/c++ which point to /usr/bin/gcc and /usr/bin/g++ respectively. For this change, the gcc package will be modified so that update-alternatives creates and manages these symlinks. | ||
In addition to modifying the gcc package, the clang package will | In addition to modifying the gcc package, the clang package will be modified so that /usr/bin/clang and /usr/bin/clang++ can be used as alternatives for /usr/bin/cc and /usr/bin/c++. The clang alternatives will have a lower priority than the gcc alternatives, so that by default, gcc will provide the /usr/bin/cc and /usr/bin/c++ implementations. | ||
The clang package currently has a run-time dependency on gcc, so this ensures that gcc will always provide the default implementation, because it's impossible to install clang without gcc. | The clang package currently has a run-time dependency on gcc, so this ensures that gcc will always provide the default implementation, because it's impossible to install clang without gcc. | ||
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Many build systems default to using /usr/bin/cc and /usr/bin/c++ as the default C/C++ compilers. Being able to easily swap out these implementation will provide a lot of flexibility within Fedora for doing things like | Many build systems default to using /usr/bin/cc and /usr/bin/c++ as the default C/C++ compilers. Being able to easily swap out these implementation will provide a lot of flexibility within Fedora for doing things like: | ||
* Setting up alternative buildroots for testing. | |||
* Installing a gcc wrapper script to /usr/bin/cc to help migrate packages to new compiler flags or to capture statistics about compiler usage. | |||
* Letting users experiment easily with alternate compilers. | |||
* Easily switch between system gcc and a development version of gcc. | |||
== Scope == | == Scope == | ||
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<!-- What work do other developers have to accomplish to complete the feature in time for release? Is it a large change affecting many parts of the distribution or is it a very isolated change? What are those changes?--> | <!-- What work do other developers have to accomplish to complete the feature in time for release? Is it a large change affecting many parts of the distribution or is it a very isolated change? What are those changes?--> | ||
* Release engineering: [https://pagure.io/releng/issues | * Release engineering: [https://pagure.io/releng/issues/9120] (a check of an impact with Release Engineering is needed) <!-- REQUIRED FOR SYSTEM WIDE CHANGES --> | ||
<!-- Does this feature require coordination with release engineering (e.g. changes to installer image generation or update package delivery)? Is a mass rebuild required? include a link to the releng issue. | <!-- Does this feature require coordination with release engineering (e.g. changes to installer image generation or update package delivery)? Is a mass rebuild required? include a link to the releng issue. | ||
The issue is required to be filed prior to feature submission, to ensure that someone is on board to do any process development work and testing, and that all changes make it into the pipeline; a bullet point in a change is not sufficient communication --> | The issue is required to be filed prior to feature submission, to ensure that someone is on board to do any process development work and testing, and that all changes make it into the pipeline; a bullet point in a change is not sufficient communication --> | ||
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<!-- REQUIRED FOR SYSTEM WIDE CHANGES --> | <!-- REQUIRED FOR SYSTEM WIDE CHANGES --> | ||
This change has no other dependencies besides the changes to the gcc and clang packages. | |||
== Contingency Plan == | == Contingency Plan == | ||
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Release notes will be added for this change. | |||
== Release Notes == | == Release Notes == | ||
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Release Notes are not required for initial draft of the Change Proposal but has to be completed by the Change Freeze. | Release Notes are not required for initial draft of the Change Proposal but has to be completed by the Change Freeze. | ||
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The user /usr/bin/cc and /usr/bin/c++ symlinks are now managed by update-alternatives. If you would like to change these symlinks to point to another compiler, like clang, for example, you can use these commands: | |||
`update-alternatives --set cc /usr/bin/clang` | |||
`update-alternatives --set c++ /usr/bin/clang++` | |||
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[[Category:SelfContainedChange]] | <!--[[Category:SelfContainedChange]]--> | ||
[[Category:SystemWideChange]] | |||
Latest revision as of 15:20, 11 February 2021
Use update-alternatives for /usr/bin/cc and /usr/bin/c++
Summary
Modify the gcc package so that the /usr/bin/cc and /usr/bin/c++ symlinks are managed by update-alternatives.
Owner
- Name: Tom Stellard
- Email: <tstellar@redhat.com>
Current status
- Targeted release: Fedora 34
- Last updated: 2021-02-11
- Tracker bug: #1790581
- Release notes tracker: #431
Detailed Description
The gcc package currently installs symlinks to /usr/bin/cc and /usr/bin/c++ which point to /usr/bin/gcc and /usr/bin/g++ respectively. For this change, the gcc package will be modified so that update-alternatives creates and manages these symlinks.
In addition to modifying the gcc package, the clang package will be modified so that /usr/bin/clang and /usr/bin/clang++ can be used as alternatives for /usr/bin/cc and /usr/bin/c++. The clang alternatives will have a lower priority than the gcc alternatives, so that by default, gcc will provide the /usr/bin/cc and /usr/bin/c++ implementations.
The clang package currently has a run-time dependency on gcc, so this ensures that gcc will always provide the default implementation, because it's impossible to install clang without gcc.
The only way users will be able to change the /usr/bin/cc or /usr/bin/c++ implementations will be by explicitly using the update-alternatives tool.
Benefit to Fedora
Many build systems default to using /usr/bin/cc and /usr/bin/c++ as the default C/C++ compilers. Being able to easily swap out these implementation will provide a lot of flexibility within Fedora for doing things like:
- Setting up alternative buildroots for testing.
- Installing a gcc wrapper script to /usr/bin/cc to help migrate packages to new compiler flags or to capture statistics about compiler usage.
- Letting users experiment easily with alternate compilers.
- Easily switch between system gcc and a development version of gcc.
Scope
- Proposal owners: The proposal owner will implement the necessary changes in the gcc and clang packages.
- Other developers: The gcc maintainers will be responsible for reviewing and approving changes to the gcc package.
- Release engineering: [1] (a check of an impact with Release Engineering is needed)
- Policies and guidelines: No policies or guidelines will need to be updated as a result of this change.
- Trademark approval: N/A (not needed for this Change)
Upgrade/compatibility impact
This change should not impact upgradeability.
How To Test
CI tests will be added to the gcc package to ensure that /usr/bin/cc and /usr/bin/c++ still point to /usr/bin/gcc and /usr/bin/g++ when installed. There will also be a CI test added to the clang package to ensure that /usr/bin/gcc and /usr/bin/g++ remain the default when clang is installed.
User Experience
This change will give users a much better way to experiment using other compilers for their own development. They will be able to easily switch between different compilers without having to modify their projects build system or make non-standard changes to their Fedora system.
Dependencies
This change has no other dependencies besides the changes to the gcc and clang packages.
Contingency Plan
- Contingency mechanism: (What to do? Who will do it?) Proposal Owner will revert changes made to gcc and clang packages and rebuild.
- Contingency deadline: If the changes are not complete by 2 weeks before the mass rebuild, then we will consider postponing to the next Fedora release and back out any changes that were made.
- Blocks release? No
- Blocks product? None
Documentation
Release notes will be added for this change.
Release Notes
The user /usr/bin/cc and /usr/bin/c++ symlinks are now managed by update-alternatives. If you would like to change these symlinks to point to another compiler, like clang, for example, you can use these commands:
update-alternatives --set cc /usr/bin/clang
update-alternatives --set c++ /usr/bin/clang++