Yeah, I wouldn't have expected that either, but if that's what you're seeing it's hard to argue otherwise. I don't think that's an inherent behavior of LTO, but it might be an unintended side effect somehow, maybe pulled in indirectly? It's probably worth a Jira ticket.
Gabe On Mon, May 24, 2021 at 1:48 PM Bobby Bruce <bbr...@ucdavis.edu> wrote: > In regards to debug symbols on the stable branch: All i can say for sure > is the debug symbols are being stripped right now with LTO enabled by > default, and they aren't stripped if you pass `--no-lto`. I wouldn't have > expected LTO to work this way, but this is our observation and one of the > reason's we're going to disable it by default. > > -- > Dr. Bobby R. Bruce > Room 3050, > Kemper Hall, UC Davis > Davis, > CA, 95616 > > web: https://www.bobbybruce.net > > > On Mon, May 24, 2021 at 1:43 PM Gabe Black <gabe.bl...@gmail.com> wrote: > >> I don't think LTO strips debug symbols... But yes, LTO does significantly >> increase link time if your machine doesn't have lots of cores to >> parallelize the link. It slows it down in general, but with gcc you can >> parallelize the link with LTO where you can't without LTO for some reason, >> and that outweighs the other overhead if you have enough cores to throw at >> it. >> >> Especially when running in a virtual machine, you might just be running >> out of memory. LTO will use more ram, and if you run out things will fail >> in potentially strange ways. >> >> It sounds like you have a workaround for now so this may be a moot point, >> but in general, when you report compiler errors (or errors in general) it's >> very helpful to provide the error output instead of just describing the >> errors. That provides a lot of helpful detail which can make diagnosing the >> problem much easier. >> >> Gabe >> >> On Mon, May 24, 2021 at 1:07 PM Bobby Bruce via gem5-users < >> gem5-users@gem5.org> wrote: >> >>> Thanks for the report Eliot. In this case there's no need to file a bug >>> report as we're about to produce a minor release of gem5 that will off LTO >>> by default. I'm not familiar with this particular problem you are facing, >>> but we've found we need to turn it off for other reasons (1. It increases >>> links times for some users to unacceptable levels and 2. LTO strips debug >>> symbols which you'll need if you want to run tools such as GDB). >>> >>> I'm hoping we can ship the minor release sometime this week! >>> >>> -- >>> Dr. Bobby R. Bruce >>> Room 3050, >>> Kemper Hall, UC Davis >>> Davis, >>> CA, 95616 >>> >>> web: https://www.bobbybruce.net >>> >>> >>> On Mon, May 24, 2021 at 12:43 PM Eliot Moss via gem5-users < >>> gem5-users@gem5.org> wrote: >>> >>>> Dear Gem5-ers: >>>> >>>> I have been trying to build Gem5 out of the box, for x86, on a >>>> VirtualBox >>>> virtual machine set up for 64-bit Ubuntu 20.04 ("focal"). I can do >>>> >>>> scons build/X86/gem5.opt >>>> >>>> but it will succeed only if I disable link time optimization LTO using >>>> --no-lto. I've tried various versions GCC - 7, 8, 9, and 10 - and all >>>> produce the same result. (I think the key thing is probably something >>>> in >>>> binutils, but I don't know what version to try to obtain, and this >>>> version of >>>> Ubuntu does not readily offer anything other than 2.34.) >>>> >>>> Searching the web about this general problem mostly produces the >>>> "solution" of >>>> disabling LTO. So, where should we / I file a bug report? By turning >>>> on LTO >>>> reporting, I have found that the proximal cause is that decoder.o does >>>> not >>>> have a .debug_str section and yet there are a huge number of references >>>> to >>>> things that should be there (labels, I guess - the decode *would* have >>>> a lot >>>> of those!). >>>> >>>> Regards - Eliot >>>> _______________________________________________ >>>> gem5-users mailing list -- gem5-users@gem5.org >>>> To unsubscribe send an email to gem5-users-le...@gem5.org >>>> %(web_page_url)slistinfo%(cgiext)s/%(_internal_name)s >>>> >>> _______________________________________________ >>> gem5-users mailing list -- gem5-users@gem5.org >>> To unsubscribe send an email to gem5-users-le...@gem5.org >>> %(web_page_url)slistinfo%(cgiext)s/%(_internal_name)s >> >>
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