Author: Benjamin Coburn

This was useful to me, maybe it will be useful to you:

2^31 – 1 = 2147483647 = highest signed 32 bit integer

2147483647 milliseconds = 24.855 days

2^32 – 1 = 4294967296 = highest unsigned 32 bit integer

4294967296 milliseconds = 49.710 days

If you are debugging a problem that has a change in behavior around 25-26 days, or at about 50 days (say for example that your product includes an automatic backup system, which gets into a loop and attempts to backup constantly if you set an interval above 25 days), one place to look is for integer overflow of a 32 bit millisecond counter somewhere.  Something like this is probably behind these two different (!) bugs in the Boeing 787 control avionics:

https://www.seattletimes.com/business/boeing-aerospace/faa-orders-787-safety-fix-reboot-power-once-in-a-while/ (reboot every 22 days -> 2^31 milliseconds)

https://www.theguardian.com/business/2015/may/01/us-aviation-authority-boeing-787-dreamliner-bug-could-cause-loss-of-control (reboot every 248 days -> 2^31 hundredths of a second)

 

 

 

I’ve been working on compiling a particularly recalcitrant C program recently, about which more later.  A large part of the difficulty is that I’m also having to learn the how to get enough output from the C compiler (in this case GCC) to figure out exactly what is going wrong.

Here are some compiler flags that make this easier:

-v for “verbose” output, prints compiler version information, the exactly command line used by Make to invoke the compiler.  It also prints the list of search paths used for #include directives, which is extremely useful.

​​​​​​​​​​​​-​H to print the full name of every included header file, so you can figure out exactly which version of stdio.h is missing the L_cuserid definition.

Running make with -jn to run multiple builds in parallel makes this sort of output very confusing, because the output from different builds is interleaved in no particular order.  I solved this by running make -j4 to get a quick but impossible to read build, then just make to give one build with a clean log.  The second build is fast because it is incremental, only the parts of the system that failed to build the first time will be recompiled.