[Bug c++/10344] Pretty printers that call into inferior could crash GDB

["pmuldoon at redhat dot com" <sourceware-bugzilla at sourceware dot org>]

------- Additional Comments From pmuldoon at redhat dot com  2009-08-26 13:47 -------
I looked at this a little today. I wanted to see if similar results happen with
the work on the archer-pmuldoon-python-value-infcall branch. The same results
occur. 

However I do not believe this to be an issue with inferior function calls, but a
peculiarity/side-effect with GDB's UI levels. If, given the original test case,
we just make the call directly within the GDB command line, I see:

 python gdb.parse_and_eval("Foo::print(0x123)")

Program received signal SIGSEGV, Segmentation fault.
0x0000000000400560 in Foo::print 
this=0x123) at t.cc:11
11	  return *p; // crash!
Traceback (most recent call last):
  File "<string>", line 1, in <module>
RuntimeError: The program being debugged was signaled while in a function called
from GDB.
GDB remains in the frame where the signal was received.
To change this behavior use "set unwindonsignal on".
Evaluation of the expression containing the function
(Foo::print() const) will be abandoned.
When the function is done executing, GDB will silently stop.
Error while executing Python code. 
 

I noted the internal assert raised about uiout levels in the original bug report
and decided to investigate this message:

"../../gdb/ui-out.c:129: internal-error: push_level: Assertion
`uiout->level >= 0 && uiout->level < MAX_UI_OUT_LEVELS' failed.

So while debugging GDB I noted that that the currently maximum used uiout->level
is 3 from a "directly" called function via parse_and_eval. When this call is
made from within a Python pretty printer, the  uiout->level exceeds the limit
specified MAX_UI_OUT_LEVELS (which is 6), and the call to error() reporting the
signal condition in the inferior function call cannot be printed. This triggers
an internal GDB error condition. 

Changing the MAX_UI_OUT_LEVELS to 7 "fixed" the problem, and the call proceeded
as it should. I do not know why the uiout levels usage is so increased via a the
pretty printer, or indeed know very much about uiout levels at all. Or why the
level is set at 6 in the code. But I thought I would produce my notes here.

-- 


http://sourceware.org/bugzilla/show_bug.cgi?id=10344

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