[GitHub] [trafficserver] zwoop commented on pull request #9481: Eliminates padding from some common structs

["zwoop (via GitHub)" <gi...@apache.org>]

zwoop commented on PR #9481:
URL: https://github.com/apache/trafficserver/pull/9481#issuecomment-1452072645

   Yeh, we've done this in the past as well, things just creeps up. I think longer term (intern maybe, good idea Craig) would be to make a very consistent layout of all structs and classes (in this order), one section for public and one section for private:
   
   1. All 64-bit types / pointers // (these will never be padded, so could go last as well
   2. All enum types // These can vary in size, I think, typically 2 bytes maybe ?
   3. All bitfields
   4. All bool types, or other 1 byte types
   5. All 32-bit types
   
   This won't solve all padding issues, but, it at least avoids a lot of them. Our HttpSM.h is particularly messy, I fixed some of it, but it was going back and forth between public / private. I fixed some of that, but not all.
   
   Additionally, it can help to arrange  the public vs private sections in a way that the padding between the two is minimized. This may require reordering the list above around those boundaries.
   
   I used a tool call pahole for this. It's definitely not great, because of our class structures and stuff, and doesn't do an awesome job with classes. Maybe there are better tools to investigate, or, maybe just use `-Wpadding` ?


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