If you look at x86 compiler output (or if, like me, you’re looking at a crash caused by some software that tried to detour an API), you may see an instruction ud2. What’s up with that? The ud2 instruction is … Read more
February 3, 2024 Photo by Jonathan Kemper on Unsplash Working in C or C++ requires some awareness of undefined behavior: what it is, what its effects are, and how to avoid tripping over it. For simplicity, I will just talk … Read more
Happy with my recent breakthrough in understanding C integer divisions after weeks of struggle, I was minding my own business having fun writing integer arithmetic code. Life was good, when suddenly… zsh: segmentation fault (core dumped). That code wasn’t messing … Read more
The other day I discovered that 32-bit FreeBSD 11.2 has strange trouble running in an emulated environment. Utilities like ping or top would just hang when trying to print floating-point numbers through printf(). The dtoa() library routine was getting stuck … Read more
Considering how important “undefined behavior” has become to C semantics and the ISO/IEC JTC1/SC22/WG14 Committee, the lack of any reference to it in the K&R ANSI book is notable and the description in the 1999 C Rationale was quite modest. … Read more