| Summary: | gcc6 fails when optimizing c++ code for nightly (firefox development version) | ||||||
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| Product: | [Fedora] Fedora | Reporter: | stan <gryt2> | ||||
| Component: | gcc | Assignee: | Jakub Jelinek <jakub> | ||||
| Status: | CLOSED NOTABUG | QA Contact: | Fedora Extras Quality Assurance <extras-qa> | ||||
| Severity: | unspecified | Docs Contact: | |||||
| Priority: | unspecified | ||||||
| Version: | rawhide | CC: | davejohansen, gryt2, jakub, jwakely, law, mpolacek | ||||
| Target Milestone: | --- | ||||||
| Target Release: | --- | ||||||
| Hardware: | Unspecified | ||||||
| OS: | Unspecified | ||||||
| Whiteboard: | |||||||
| Fixed In Version: | Doc Type: | Bug Fix | |||||
| Doc Text: | Story Points: | --- | |||||
| Clone Of: | Environment: | ||||||
| Last Closed: | 2016-03-17 15:29:41 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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Please try -flifetime-dse=1 or -fno-lifetime-dse and/or -fno-delete-null-pointer-checks, forgot which of these violates firefox, whether trying to preserve data from before construction to after construction, or calling methods on NULL pointers (or both). Created attachment 1135307 [details]
The .mozconfig that I am using to compile nightly.
Copy this into ~/.mozconfig in order to use it to compile nightly instead of the built in defaults.
@comment1, thanks jakub for the fast response. Will try those (will search first to profit from other's experience) to see what works. Progress! See https://gcc.gnu.org/gcc-6/porting_to.html for some details. Thanks for that reference. Very informative. Once I confirm that following the advice in the reference allows nightly to compile, I'll close this ticket, as it isn't a problem with gcc 6. I tried several variations of options, and nightly crashes on start with any optimization regardless of what I do. ac_add_options --enable-optimize=" -Wall -std=gnu++11 -O3" ac_add_options --enable-optimize=" -Wall -std=gnu++98 -O3" # this wouldn't compile ac_add_options --enable-optimize=" -Wall -fno-delete-null-pointer-checks -O3" ac_add_options --enable-optimize=" -Wnull-dereference -fno-delete-null-pointer-checks -O3" I don't know whether it is gcc or nightly with the problem. I'm out of my depth here. So, I'll just drop it. I leave it up to you whether to close the ticket. Did you try -fno-lifetime-dse ? Aarrrgh! No, I didn't. I'll give that a try today. Thanks for the question. That was it! When I used ac_add_options --enable-optimize=" -Wall -fno-lifetime-dse -fno-delete-null-pointer-checks -O3" nightly compiled fine, and started and is running fine. I'm using it to write this message. So, I assume that means there is no issue with g++ optimization in gcc 6, and that it is coding style in nightly that is the cause of this because it is to a different standard than gcc 6. If that is the case, then I think this ticket can be closed as NOTABUG. Thanks for the help. Not a gcc bug. |
Description of problem: I keep an hg repository of the firefox development version, nightly. I compile it on f21 with gcc 4.9 and rawhide (f25) with gcc6. With gcc 4.9, I can use -O3 and the resulting executable runs fine. With gcc6, neither -O2 or -O3 will run. The compile appears to complete successfully, but gets a seg fault on start. If I compile using gcc6, with -O0, the resulting executable runs fine, though slowly. Version-Release number of selected component (if applicable): Name : gcc Version : 6.0.0 Release : 0.15.fc25 Architecture: x86_64 How reproducible: Every time. Steps to Reproduce: 1. Clone the hg repository for nightly 2. Default optimization is -O2, have to add ac_add_options --enable-optimize=" -O3 " if O3 wanted. 3. cd into the directory and run ./mach build 4. run ./mach install (the appended .mozconfig will put into /usr/local) 5. Observe the crash Actual results: Successful build, crash on start Expected results: Nightly runs fine Additional info: This is a bug at mozilla with some information about tests I've done to work around this. It's actually about another problem, but contains the extra data. https://bugzilla.mozilla.org/show_bug.cgi?id=1245076 I'll attach the .mozconfig I use to build nightly. It's possible this isn't a bug in gcc at all, but the fact that the code compiles and runs fine without optimization, -O0, leads me to believe it is. I've compiled C programs with gcc 6 and -O3, and they have worked correctly. So it could be only in g++.