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10446 :: More info on NimMain procedure

• Zeldapedia (orginal) [2023-08-28T05:34:46+02:00] view original

  Hello, I am a first time user of Nim and was confused about this procedure I've seen thrown around quite a bit with no real explanation of what exactly it is, what it does, if it is necessary, added automatically, etc.. The docs mention it's necessary for iOS and Android executables, but I've also seen it being used (sometimes) for DLLs. I noticed that it is imported from C, and after doing some digging I think this it it (?)

  N_LIB_EXPORT N_CDECL(void, NimMain)(void) {
          void (*volatile inner)(void);
          PreMain();
          inner = NimMainInner;
          initStackBottomWith((void *)&inner);
          (*inner)();
  }
  Run

  Though this doesn't really help. Is this procedure related to, in any way, the --nomain tag you can pass to the transpiler?? Any info at all would be helpful, thanks

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• Araq (orginal) [2023-08-28T08:32:36+02:00] view original

  It is the entry point into your program, accessible from C. As a first time user of Nim you don't have to know about it.

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• awr1 (orginal) [2023-08-28T08:38:36+02:00] view original

  approximately, NimMain:

  • pulls in command line arguments
  • links to all {.dynlib.} procedures
  • if needed, starts TLS emulation
  • if needed, start the GC
  • if needed, registers all nim-side procedures and globals with the HCR (hot-code reloader)
  • initalizes the nim-side callstack + exception handler
  • executes system.nim
  • executes user top-level runtime code

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• PMunch (orginal) [2023-08-28T10:51:30+02:00] view original

  Just to add, it is also connected to the --noMain flag you pass to the _compiler. That flag basically means "don't automatically call the NimMain procedure", so often when you see someone calling NimMain they are also compiling using --noMain.

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