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3054 :: segfault using string from c?

• segmentation_fault (orginal) [2017-07-16T18:57:54+02:00] view original

  How can you pass a char * to nim, ive been trying for a while but i keep getting segfault.

  if i use:

  proc read_csv(fpx: cstring): void {.exportc.} =
      let fp: string = cast[string](fpx)
      var s = newFileStream(fp, fmRead)
      if s == nil:
          echo "file not found"
          return
  Run

  then there's a segfault at newFileStream

  if i use

  proc read_csv(fp: string): void {.exportc.} =
      var s = newFileStream(fp, fmRead)
      if s == nil:
          echo "file not found"
          return
  Run

  then the first 15 chars get truncated, but i still also get a segfault at newFileStream

  i tried calling the function from c with read_csv("/path/to/csv");

  if i run the nim file instead of compiling to c it works.

  Also i found out that if i hardcode the value i get a segfault here STRING_LITERAL(TM_xgSOGG8fvQlwPH9bPyp9bbTg_6, "path_here", 36);

  thx

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• yglukhov (orginal) [2017-07-16T21:02:06+02:00] view original

  First way is correct, except conversion from cstring to string should be made with $.

  proc read_csv(fpx: cstring): void {.exportc.} =
      let fp = $fpx
      var s = newFileStream(fp, fmRead)
      if s == nil:
          echo "file not found"
          return
  Run

---

• segmentation_fault (orginal) [2017-07-16T21:46:40+02:00] view original

  yes i tried that but if i do $fpx i get a segfault on the $fpx valgrind segfult line the compiled code is at fp = cstrToNimstr(fpx);

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• segmentation_fault (orginal) [2017-07-16T21:53:27+02:00] view original

  if it helps this is the valgrind output

  ==9355== Process terminating with default action of signal 11 (SIGSEGV)
  ==9355==  Access not within mapped region at address 0x0
  ==9355==    at 0x665CA1B: lowGauge_3mwQtFaBTgevFrybZdgUNw (stdlib_system.c:1380)
  ==9355==    by 0x6664A53: prepareForInteriorPointerChecking_Zqr3EQAAcehIfp3uSECEuQsystem (stdlib_system.c:1418)
  ==9355==    by 0x6664A53: collectCTBody_zoTIuavlrCHyw3B8MBaLJA_2 (stdlib_system.c:4046)
  ==9355==    by 0x6664BF7: collectCT_zoTIuavlrCHyw3B8MBaLJA (stdlib_system.c:4115)
  ==9355==    by 0x6664ED8: rawNewObj_QBPo5VW2O56Eeh8hPbQ7Pg (stdlib_system.c:4210)
  ==9355==    by 0x666512F: newObjNoInit (stdlib_system.c:4226)
  ==9355==    by 0x66651B3: rawNewStringNoInit (stdlib_system.c:4243)
  ==9355==    by 0x6665251: toNimStr (stdlib_system.c:4707)
  ==9355==    by 0x665A7AB: read_csv (fib.c:335)
  ==9355==    by 0x6658C39: first_func (fib.c:22)
  ==9355==    by 0x4E9B9E: PyCFunction_Call (in /home/x/x/venv/bin/python3.5)
  ==9355==    by 0x524413: PyEval_EvalFrameEx (in /home/x/x/venv/bin/python3.5)
  ==9355==    by 0x52D2E2: ??? (in /home/x/x/venv/bin/python3.5)
  Run

  and this is my c code

  #include "nimcache/fib.h"
  #include <stdio.h>
  #include <Python.h>
  static PyObject* first_func(PyObject* self, PyObject* args)
  {
      char * value;
      
      if (!PyArg_ParseTuple(args, "s", &value))
          return NULL;
      
      read_csv("/home/x/Downloads/x.csv");
      
      return Py_BuildValue("f", 1.1);
  }
  Run

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• yglukhov (orginal) [2017-07-16T21:54:37+02:00] view original

  What's your C code then? Are you calling this proc from C program or from Nim program? If C program, Nim's GC might not be initialized.

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• yglukhov (orginal) [2017-07-16T21:58:20+02:00] view original

  Ok, so the problem is likely that Nim runtime is not initialized. Try setupForeignThreadGc() at the beginning of your proc. TBH, i don't remember exactly how this is done...

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• segmentation_fault (orginal) [2017-07-16T22:13:58+02:00] view original

  thx this got the $fpx working now getting a segfault when i do open(), ill investigate further i guess its something related it works perfectly fine when not calling it from c.

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• segmentation_fault (orginal) [2017-07-16T22:20:30+02:00] view original

  ok fixed i had to call NimMain(); this fixed everything

  PyMODINIT_FUNC
  PyInit_fib(void)
  {
      NimMain();
      return PyModule_Create(&nim_module);
  }
  Run

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