Date: Fri, 26 Oct 2012 10:21:15 +0800 From: Brian Wang <brian.wang.0721@...il.com> To: musl@...ts.openwall.com Subject: Re: Difference between -O2 and -g Re-attaching the strace logs... (seems to be stripped out by the server last time) On Fri, Oct 26, 2012 at 10:04 AM, Brian Wang <brian.wang.0721@...il.com> wrote: > On Fri, Oct 26, 2012 at 9:40 AM, Rich Felker <dalias@...ifal.cx> wrote: >> On Fri, Oct 26, 2012 at 09:31:56AM +0800, Brian Wang wrote: >>> Hello all, >>> >>> I am experiencing a rather strange problem... >>> >>> I have an oldish kdrive/Xfbdev that works on my ARM device with >>> CodeSourcery toolchains. >>> Now, I tried it with musl (0.9.6 and the recent git master branch as well). >>> First it failed to find the screen and refused to start. After some naive >>> attempts with printf without success, I recompiled it with -g and no >>> -Ox with the hope that gdbserver >>> would help pin point the problem. However, with only -g, it runs! >> >> -g should have absolutely no effect on code behavior, but it sounds >> like your two setups are "-O2" and "-O0 -g" (where the -O0 is the >> default). If that's the case, when code behaves differently with >> different optimization levels, the cause is almost surely undefined >> behavior. Another possibility is a bug in musl (possibly an >> ARM-specific bug), but if you didn't recompile musl with different >> options, I doubt that's the cause. >> >> One very simple way to get a picture of what's going on in a program >> is to run it under strace. Try saving strace logs for both the working >> version and the broken version and comparing them either manually or >> with the diff utility (although the latter may be difficult unless you >> filter out the addresses and other contnets that will naturally >> differ, so it might be easier to visually inspect). If you don't >> already have an strace built for your target, I think Aboriginal Linux >> has static binaries you can use. > > I have previously built my static strace. > I could not decipher what went wrong. Please find the strace logs for > the three binaries in question. > The source code is basically the same, except for the musl ones, > printf calls are sprinkled here and there > as my desperate attempt. > >> >> If you're having trouble analyzing the results I'd be happy to help >> you. >> >> Rich > > Thank you for your help. > > > Brian > > > > -- > brian > ------------------ > > Cool-Karaoke - The smallest recording studio, in your palm, open-sourced > http://cool-idea.com.tw/ > > iMaGiNaTiOn iS mOrE iMpOrTaNt tHaN kNoWlEdGe -- brian ------------------ Cool-Karaoke - The smallest recording studio, in your palm, open-sourced http://cool-idea.com.tw/ iMaGiNaTiOn iS mOrE iMpOrTaNt tHaN kNoWlEdGe View attachment "Xfbdev-glibc-O2.log.txt" of type "text/plain" (34094 bytes) View attachment "Xfbdev-musl-debug.log.txt" of type "text/plain" (80060 bytes) View attachment "Xfbdev-musl-O2.log.txt" of type "text/plain" (14634 bytes)
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