How to debug broken unwinding?

Milian Wolff mail@milianw.de
Wed Jun 7 12:16:00 GMT 2017


On Donnerstag, 1. Juni 2017 22:57:12 CEST Milian Wolff wrote:
> Hey all,

<snip>

>  heaptrack_gui  2228 135073.400474:     613969 cycles:
>                   108c8e [unknown] (/usr/lib/libQt5Core.so.5.8.0)
> @@ -533,8 +529,6 @@
>                   2170af [unknown] (/usr/lib/libQt5Core.so.5.8.0)
>                   297c53 QCoreApplicationPrivate::init (/usr/lib/
> libQt5Core.so.5.8.0)
>                    f7cde QGuiApplicationPrivate::init
> (/usr/lib/libQt5Gui.so. 5.8.0)
> -                 1589e8 QApplicationPrivate::init
> (/usr/lib/libQt5Widgets.so. 5.8.0)
> -                  78622 main (/home/milian/projects/compiled/other/bin/
> heaptrack_gui)
>                    20439 __libc_start_main (/usr/lib/libc-2.25.so)
>                    78299 _start (/home/milian/projects/compiled/other/bin/
> heaptrack_gui)
> 
> NOTE: this is super odd, it simply misses two frames in the middle?!

This is really quite odd - looking at the debug output, the frames in the 
middle are really just skipped for some reason:

unwind: access_mem addr 0x7ffca0a88330, val 4edc50, offset 2808
unwind: access_mem addr 0x7ffca0a88338, val 7f69bfce443a, offset 2816
unwind: pc: = 0x7f69c10fecde
found map: 7f69c1007000 7f69c1766000
dso found: libQt5Gui.so.5.8.0 /usr/lib/libQt5Gui.so.5.8.0
reported: libQt5Gui.so.5.8.0 /usr/lib/libQt5Gui.so.5.8.0, 1
unwind: QGuiApplicationPrivate::init():ip = 0x7f69c10fecde (0xf7cde)

-> so far so good, this frame is properly found inside libQt5Gui, but then:

unwind: pc: = 0x7f69bfce4439
found map: 7f69bfcc4000 7f69c0069000
dso found: libc-2.25.so /usr/lib/libc-2.25.so
reported: libc-2.25.so /usr/lib/libc-2.25.so, 1
unwind: __libc_start_main:ip = 0x7f69bfce4439 (0x20439)

-> the next frame is is supposedly the one in libc, but what happened to the 
two frames in QApplicationPrivate::init and main? I also note that no calls to 
access_mem are occuring - is this maybe some (wrong) caching in libdw or so 
that interfers here?

Any insight would be appreciated, thanks!
-- 
Milian Wolff
mail@milianw.de
http://milianw.de
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