fche changed the topic of #systemtap to: http://sourceware.org/systemtap; email systemtap@sourceware.org if answers here not timely, conversations may be logged
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<gromero> hi. I've just updated to kernel 4.12-rc6 and my previous tap that was working fine on 4.10 now halts. Is it any known regression?
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<fche> it's not a regression for old code to not work on new kernels; it's just probably a lack-of-porting
<fche> can you fpaste the errors?
<fche> hm that's very truncated, what is that, a kernel panic ?
<leitao> yes
<leitao> I have a better log, sorry
<leitao> same userspace, just upgraded from rc5 to r6
<leitao> rc6
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<fche> _stp_print_regs may be calling some kernel routine that's changed
<fche> pSeries? ppc64?
<gromero> yes
<gromero> fche: makes sense, let me try
<fche> other/ordinary stap scripts run OK though?
<leitao> it seems it is still failing.
<gromero> fche: removing print_regs() does not work either... testing a simpler script
<fche> you two working together?
<fche> or two glorious avatars of the same human brain? :)
<gromero> fche: lol
<gromero> we are working together...
<fche> try a script without print_regs()
<gromero> we did, it was the same... rebooting VM
<gromero> I'll try with a simple printf()
<drsmith> most of the time a newer kernel will just get you compile errors, but it looks like you guys got "lucky"
<leitao> drsmith, I am wondering if the problem is on kprobe or on powerpc side.
<drsmith> try a simple "hello world": stap -ve 'probe begin { printf("hello\n"); exit() }'
<drsmith> if the "hello world" works, then try a simple kernel probe, something like: stap -ve 'probe syscall.read { printf("read\n"); exit() }'
<gromero> drsmith: first hello world on begin probe works fine
<gromero> and exits fine as well
<drsmith> good
<gromero> let me try next
<gromero> second too goes well
<drsmith> hmm, good
<gromero> the problem just happens when I run the progrom to be inspected...
<drsmith> ok, can you show us the script that crashes?
<gromero> I'm using execname() == "program_name"
<gromero> sure
<gromero> removing print_regs() in the end of pp() did not worked as I mentioned...
<gromero> drsmith: fche this is the original version: https://hastebin.com/raw/ewuvoveyey
<gromero> were the problem exists, and as I mentioned commenting out print_regs() in it did not help...
<drsmith> Hmm. I think I'd try to bisect pp_() down until it doesn't crash. Then we'd know exactly what is causing the problem.
<fche> https://hastebin.com/raw/nuhubituzo <-- in this, pp_() is not even called
<gromero> fche: you are right, please consider https://hastebin.com/raw/ewuvoveyey for the analysis
<drsmith> my suspicion would be those kernel_long() calls, if it weren't for the fact that kernel_long() tries very hard to not cause a page fault.
<gromero> looks like the without kernel_long() it works...
<gromero> I'll get one of them back
<drsmith> yeah, I'd try the +0 one first
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<fche> hm, disable_pagefaults() no longer disabling pagefaults? :)
<gromero> fche: drsmith did all over again, I confirm print_regs() is the culprit
<gromero> since it's a modified versio of mine to inspect 128bits register on powerpc, it's my fault...
<drsmith> ah, ok
<gromero> drsmith: fche thanks a lot!
<gromero> I'll investigate further why that kernel change messed up all
<drsmith> if you think that modified version would be of use to others, email it to the list and we'll take a look at it and see if it makes sense to merge (minus the crash of course)
<fche> or have an april-first random-crash option
<gromero> lol
<gromero> drsmith: fche sure I'll do, but has to work without that nasty crash... inspecting 128bit registers (FP/VEC/VSX) is indeed something important on powerpc...
<gromero> stap is helping a lot, I want to contribute it back ;-)
<fche> music to our ears!
<gromero> :-)
<fche> we'd love to read (and let the world read) about your successes / failures with the tool too
<gromero> fche: sure! but I want to tell a success story :-)
<gromero> fche: I'll keep in touch :-)
<fche> better than the other kind
<gromero> haha agree
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