People hate surveys, but like being interviewed

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: Entrepreneurship

(Originally appeared on my Indie Hackers blog)

Instead of posting a link to a survey in a Facebook group with potential customers, post that you’re doing a research project and would love to interview some people that do [whatever your target market does].

Here’s my theory: People don’t like filling out surveys because it feels cold, and impersonal. On the other hand, answering questions being asked by a human interviewer, even if they are the same questions, makes them feel important because of the personal touch. Someone else is taking time from their day to ask the questions, so it’s more reciprocal.

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Reproducing a GCC 8.1 ABI compatibility bug

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: _Twitter Archive 🐤, Assembly, C++

I was reading about GCC and noticed this very suspicious warning line about an accidental compatibility break: https://gcc.gnu.org/gcc-8/changes.html

I thought it would be interesting to reproduce this. I reproduced this specific scenario they outline and compiled two translations units, one with GCC 8.1, one with an earlier version (GCC 7) and observed the segfault that happens when two incompatible calling conventions interact with each other.

Being pedantic about C++ compilation

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: _Tech 💻, C++, CMake, Linux

Takeaways:

  • Don’t assume it’s safe to use pre-built dependencies when compiling C++ programs. You might want to build from source, especially if you can’t determine how a pre-built object was compiled, or if you want to use a different C++ standard than was used to compile it.
  • Ubuntu has public build logs which can help you determine if you can use a pre-built object, or if you should compile from source.
  • pkg-config is useful for generating the flags needed to compile a complex third-party dependency. CMake’s PkgConfig module can make it easy to integrate a dep into your build system.
  • Use CMake IMPORTED targets (e.g. BZip2::Bzip2) versus legacy variables (e.g. BZIP2_INCLUDE_DIRS and BZIP2_LIBRARIES).
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struct stat notes

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: _Lab Notes 🧪, Linux

struct stat on Linux is pretty interesting

  • the struct definition in the man page is not exactly accurate
  • glibc explicitly pads the struct with unused members which is intersting. I guess to reserve space for expansion of fields
    • if you want to see the real definition, a trick you can use is writing a test program that uses a struct stat, and compiling with -E to stop after preprocessing then look in that output for the definition
  • you can look in the glibc sources and the linux sources and see that they actually have to make their struct definitions match! (i think). since kernel space is populating the struct memory and usespace is using it, they need to exactly agree on where what members are
    • you can find some snarky comments in linux about the padding, which is pretty funny. for example (arch/arm/include/uapi/asm/stat.h)
  • because the structs are explicitly padded, if you do a struct designator initialization, you CANNOT omit the designators. if you do, the padded members will be initialized instead of the fields you wanted!