| Summary: | ifunc attribute and optimization | ||||||
|---|---|---|---|---|---|---|---|
| Product: | [Fedora] Fedora | Reporter: | Jerry James <loganjerry> | ||||
| Component: | gcc | Assignee: | Jakub Jelinek <jakub> | ||||
| Status: | CLOSED EOL | QA Contact: | Fedora Extras Quality Assurance <extras-qa> | ||||
| Severity: | low | Docs Contact: | |||||
| Priority: | unspecified | ||||||
| Version: | 25 | CC: | davejohansen, jakub, jwakely, law, mpolacek | ||||
| Target Milestone: | --- | ||||||
| Target Release: | --- | ||||||
| Hardware: | x86_64 | ||||||
| OS: | Linux | ||||||
| Whiteboard: | |||||||
| Fixed In Version: | Doc Type: | Bug Fix | |||||
| Doc Text: | Story Points: | --- | |||||
| Clone Of: | Environment: | ||||||
| Last Closed: | 2017-12-12 10:49:21 UTC | Type: | Bug | ||||
| Regression: | --- | Mount Type: | --- | ||||
| Documentation: | --- | CRM: | |||||
| Verified Versions: | Category: | --- | |||||
| oVirt Team: | --- | RHEL 7.3 requirements from Atomic Host: | |||||
| Cloudforms Team: | --- | Target Upstream Version: | |||||
| Attachments: |
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This bug appears to have been reported against 'rawhide' during the Fedora 25 development cycle. Changing version to '25'. This message is a reminder that Fedora 25 is nearing its end of life. Approximately 4 (four) weeks from now Fedora will stop maintaining and issuing updates for Fedora 25. It is Fedora's policy to close all bug reports from releases that are no longer maintained. At that time this bug will be closed as EOL if it remains open with a Fedora 'version' of '25'. Package Maintainer: If you wish for this bug to remain open because you plan to fix it in a currently maintained version, simply change the 'version' to a later Fedora version. Thank you for reporting this issue and we are sorry that we were not able to fix it before Fedora 25 is end of life. If you would still like to see this bug fixed and are able to reproduce it against a later version of Fedora, you are encouraged change the 'version' to a later Fedora version prior this bug is closed as described in the policy above. Although we aim to fix as many bugs as possible during every release's lifetime, sometimes those efforts are overtaken by events. Often a more recent Fedora release includes newer upstream software that fixes bugs or makes them obsolete. Fedora 25 changed to end-of-life (EOL) status on 2017-12-12. Fedora 25 is no longer maintained, which means that it will not receive any further security or bug fix updates. As a result we are closing this bug. If you can reproduce this bug against a currently maintained version of Fedora please feel free to reopen this bug against that version. If you are unable to reopen this bug, please file a new report against the current release. If you experience problems, please add a comment to this bug. Thank you for reporting this bug and we are sorry it could not be fixed. |
Created attachment 1149496 [details] Program with an indirect function Description of problem: The attached program uses indirect function support to invoke the popcnt instruction on x86_64 CPUs that support it, with a fallback for other CPUs. The executions shown below are on a CPU that has the popcnt instruction. $ gcc -o bit_counter bit_counter.c $ ./bit_counter 0 1 2 3 4 5 6 7 8 1000 1000000 0 contains 0 bits. 1 contains 1 bits. 2 contains 1 bits. 3 contains 2 bits. 4 contains 1 bits. 5 contains 2 bits. 6 contains 2 bits. 7 contains 3 bits. 8 contains 1 bits. 1000 contains 6 bits. 1000000 contains 7 bits. $ gcc -O -o bit_counter bit_counter.c $ ./bit_counter 0 1 2 3 4 5 6 7 8 1000 1000000 0 contains 4195766 bits. 1 contains 4195766 bits. 2 contains 4195766 bits. 3 contains 4195766 bits. 4 contains 4195766 bits. 5 contains 4195766 bits. 6 contains 4195766 bits. 7 contains 4195766 bits. 8 contains 4195766 bits. 1000 contains 4195766 bits. 1000000 contains 4195766 bits. I have tried turning off every optimization listed as enabled by gcc -O -Q --help=optimizers, and even with all of them off, execution produces very large numbers as in the second example above. I recognize that indirect function support involves gcc, ld, and glibc, but I don't know which component is causing this particular problem, hence filing this against gcc for now. Version-Release number of selected component (if applicable): gcc-6.0.0-0.20.fc25.x86_64 binutils-2.26-16.fc25.x86_64 glibc-2.23.90-11.fc25.x86_64 How reproducible: Always. Steps to Reproduce: 1. Compile the attached program with the options shown above. 2. Run the program. Actual results: When built with optimization, the program produces incorrect results. Expected results: Correct results with optimization on. Additional info: I have discovered two workarounds that produce correct results even if the program is compiled with optimization: 1. Declare bit_counter as extern instead of static. 2. Add __attribute__((optimize ("O0"))) to resolve_bit_counter.