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12788 :: sqlite segfault in dynlib

• cmc (orginal) [2025-04-14T10:25:43+02:00] view original

  I'm having an issue I'm having hard time to trace.

  I have a setup where a dynamically loaded library opens a sqlite database and it segfaults.

  
  import dynlib, os
  
  let lib = loadlib("./libbar.so")
  if lib.isNil:
    raise newException(LibraryError, "could not load libbar.so")
  
  let runBar = cast[proc () {.nimcall.}](lib.checkedSymAddr("runBar"))
  
  runBar()
  Run

  
  import db_connector/db_sqlite
  
  proc NimMain() {.cdecl, importc.}
  proc library_init() {.exportc, dynlib, cdecl.} =
    NimMain()  # is this done correctly?
  proc library_deinit() {.exportc, dynlib, cdecl.} =
    GC_FullCollect()
  
  proc runBar() {.exportc,dynlib,nimcall.} =
    let db = open("bar.db", "", "", "")  # remove this line for no segfault
    echo "opened."
  Run

  
  $ nim c --d:useMalloc foo.nim
  $ nim c --noMain --app:lib --d:useMalloc -o:libbar.so bar.nim
  $ ./foo
  /path/to/foo.nim(9)   foo
  SIGSEGV: Illegal storage access. (Attempt to read from nil?)
  Segmentation fault (core dumped)
  Run

  It's not a db_connector issue, the crash happens within the sqlite3_open C function (same behavior with other Nim sqlite libs).

  It's also not a C issue, doing the same thing with C code works fine.

  
  // foo.c
  #include <stdio.h>
  #include <dlfcn.h>
  
  int main(int argc, char *argv[]) {
          char *lib = "libbar.so"
          void *lib_ptr = dlopen(lib, RTLD_LAZY);
          if (!lib_ptr) {
                  fprintf(stderr, "error loading lib %s (%s)\n", lib, dlerror());
                  return 1;
          }
          void (*func_ptr)() = dlsym(lib_ptr, "runBar");
          if (!func_ptr) {
                  fprintf(stderr, "error loading func() (%s)\n", dlerror());
                  return 1;
          }
          func_ptr();
  }
  Run

  
  // bar.c
  #include <stdio.h>
  #include <sqlite3.h>
  
  void runBar() {
          sqlite3 *db;
          sqlite3_open("bar.db", &db);
          printf("opened.\n");
  }
  Run

  
  $ gcc foo.c -o foo
  $ gcc -c bar.c FPIC
  $ gcc bar.o -shared -lsqlite3 -o libbar.so
  $ gcc foo.o -shared -lsqlite3 -o libfoo.so
  $ ./foo
  opened.
  Run

  I suspect it has something to do with how I'm bootstrapping Nim in the dynlib bar.nim but I'm at a bit of a loss on how to track down the problem.

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• Araq (orginal) [2025-04-14T11:11:54+02:00] view original

  I don't know either attach GDB to see where it fails or run it through valgrind.

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• cmc (orginal) [2025-04-14T11:53:14+02:00] view original

  Thank you! No symbols from gdb so far but while trying to fix that I noticed libbar.so can be loaded if omitting --noMain.

  So that was it- the dynamic loader appears not to be calling library_init() on my system for some reason. This works:

  
  import db_connector/db_sqlite
  
  proc NimMain() {.importc, cdecl.}
  
  proc library_init() {.exportc,dynlib,cdecl.} =
    echo "LOADED"  # this doesn't happen
  
  proc runBar() {.exportc,dynlib,cdecl.} =
    NimMain()
    let db = open("foo.db","","","")
    echo "loaded"
  Run

  So for now I'll be using an additional init proc in bar.nim and calling it manually in foo.nim.

  Of course it would be interesting to know if library_init() is generally considered reliable enough to be used and there's something going on, or if it just normal that it doesn't work on my system but might work on others.

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