Re: maximum number of backtrace frames logged by backtrace_functions

On 2022/02/18 19:59, Peter Eisentraut wrote:
> On 18.02.22 09:24, Fujii Masao wrote:
>> Or even backtrace should be logged by write_stderr() so that it's written to eventlog if necessary? I just wonder
whybacktrace_symbols_fd() is used only in ExceptionalCondition().
 
> 
> Probably because it was simpler.  It would also make sense to convert the whole thing to use write_stderr()
consistently.
+1
Attached is the updated version of the patch that uses write_stderr() to log the backtrace in assertion failure case.

+        if (nframes >= lengthof(buf))
+            appendStringInfo(&errtrace, "\n(backtrace limited to %zu frames)",
+                             lengthof(buf));

I found this doesn't work on FreeBSD, at least FreeBSD 13 that cfbot uses on Cirrus CI. When the backtrace is larger
than100, on FreeBSD, backtrace() seems to write the *99* (not 100) most recent function calls to the buffer. That is,
thevariable "nframes" is 99 while lengthof(buf) indicates 100. So the above message about backtrace limit will never be
loggedon FreeBSD. OTOH, on Linux and MacOS, backtrace() writes the 100 most recent function calls. I'm not sure if such
abehavior on FreeBSD is expected or a bug.
 

To issue the message whatever OS is, probably we need to modify set_backtrace() as follows, for example. But is this
overkill?Thought?
 


-        void       *buf[100];
+#define    BACKTRACE_MAX_FRAMES    100
+        void       *buf[BACKTRACE_MAX_FRAMES + 1];
          int            nframes;
          char      **strfrms;
  
          nframes = backtrace(buf, lengthof(buf));
+        if (nframes > BACKTRACE_MAX_FRAMES)
+            nframes = BACKTRACE_MAX_FRAMES;
          strfrms = backtrace_symbols(buf, nframes);
          if (strfrms == NULL)
              return;
  
          for (int i = num_skip; i < nframes; i++)
              appendStringInfo(&errtrace, "\n%s", strfrms[i]);
+        if (nframes >= BACKTRACE_MAX_FRAMES)
+            appendStringInfo(&errtrace, "\n(backtrace limited to %d frames)",
+                             BACKTRACE_MAX_FRAMES);

Regards,

-- 
Fujii Masao
Advanced Computing Technology Center
Research and Development Headquarters
NTT DATA CORPORATION