[lldb-dev] Missing function arguments in the backtrace

[Jason Molenda]

Ashok, for what it's worth I can't see what would cause this difference between the two runs based on the log files.

Is it possible that lldb is stopped at different places when the thread backtrace all is invoked?  The lldb unwind log isn't printing the pc values of thread 1 frame 0.  thread 1 is clearly the same in both - we have the exact same pc value and we're using the same unwind instructions from the eh_frame.

This is a little odd  -

  th1/fr2 looking for register saved location for reg 2
 th1/fr1 did not supply reg location for 2 (rcx) because it is volatile
  th1/fr2 looking for register saved location for reg 16
 th1/fr1 supplying caller's saved reg 16's location, cached
  th1/fr2 looking for register saved location for reg 8
 th1/fr1 did not supply reg location for 8 (r8) because it is volatile

Why would lldb be trying to examine something in rcx or r8 in frame 2 here?  There must be a variable whose location list says it is live at the call site in that register - poor DWARF from the compiler.

The fact that we don't see the same thing in the bt-fail.log case makes me wonder if the debug info isn't different -- or absent?


On Sep 24, 2013, at 1:26 PM, Thirumurthi, Ashok <ashok.thirumurthi at intel.com> wrote:

> I have an Ubuntu 12.10 machine where inferior_asserting() succeeds when functionalities/inferior-asserting is run in isolation with either of clang or gcc, but fails when dotest.py is used to run the full suite.  When it fails, the backtrace is missing all function arguments.  A diff of the attached logs illustrates that RegisterContextLLDB comes up with a more complete register set in the passing case.
> 
> Note: th1/fr1 frame uses eh_frame CFI for full UnwindPlan
> 
> Any guesses from the logs where I'd be looking to root cause this funkiness??
> 
> - Ashok
> 
>  th1/fr2 looking for register saved location for reg 16
> th1/fr1 supplying caller's saved reg 16's location, cached
>  th1/fr2 looking for register saved location for reg 1
> th1/fr1 could not supply caller's reg 1 location
> th1/fr0 supplying caller's register 1 from the live RegisterContext at frame 0
> th1/fr1 looking for register saved location for reg 1
> th1/fr0 supplying caller's saved reg 1's location, cached
> th1/fr0 looking for register saved location for reg 1
> th1/fr0 passing along to the live register context for reg 1
>  th1/fr2 looking for register saved location for reg 16
> th1/fr1 supplying caller's saved reg 16's location, cached
>  th1/fr2 looking for register saved location for reg 12
> th1/fr1 could not supply caller's reg 12 location
> th1/fr0 supplying caller's register 12 from the live RegisterContext at frame 0
> th1/fr1 looking for register saved location for reg 12
> th1/fr0 supplying caller's saved reg 12's location, cached
> th1/fr0 looking for register saved location for reg 12
> th1/fr0 passing along to the live register context for reg 12
>  th1/fr2 looking for register saved location for reg 16
> th1/fr1 supplying caller's saved reg 16's location, cached
>  th1/fr2 looking for register saved location for reg 6
> th1/fr1 could not supply caller's reg 6 location
> th1/fr0 supplying caller's saved reg 6's location, cached
> th1/fr1 looking for register saved location for reg 6
> th1/fr0 supplying caller's saved reg 6's location, cached
> th1/fr0 looking for register saved location for reg 6
> th1/fr0 passing along to the live register context for reg 6
>  th1/fr2 looking for register saved location for reg 16
> th1/fr1 supplying caller's saved reg 16's location, cached
>  th1/fr2 looking for register saved location for reg 2
> th1/fr1 did not supply reg location for 2 (rcx) because it is volatile
>  th1/fr2 looking for register saved location for reg 16
> th1/fr1 supplying caller's saved reg 16's location, cached
>  th1/fr2 looking for register saved location for reg 8
> th1/fr1 did not supply reg location for 8 (r8) because it is volatile
> 
> 
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