on OSX, debugging (w gdb or lldb) a nim program crashes at the 1st call to `execCmdEx`

[timotheecour]

BUG:can't debug (with lldb) a nim binary that calls execCmdEx

lldb /tmp/nim//app
(lldb) target create "/tmp/nim//app"
(lldb) r
Process 98697 launched: '/tmp/nim/app' (x86_64)
ok1b.1
/Users/timothee/git_clone/nim/timn/bugs/stdlib/t22_lldb_execCmdEx.nim(12) t22_lldb_execCmdEx
/Users/timothee/git_clone/nim/timn/bugs/stdlib/t22_lldb_execCmdEx.nim(9) test
/Users/timothee/git_clone/nim/Nim/lib/pure/osproc.nim(1330) execCmdEx
/Users/timothee/git_clone/nim/Nim/lib/pure/streams.nim(280) readLine
/Users/timothee/git_clone/nim/Nim/lib/pure/streams.nim(162) readChar
/Users/timothee/git_clone/nim/Nim/lib/pure/streams.nim(87) readData
/Users/timothee/git_clone/nim/Nim/lib/pure/streams.nim(413) fsReadData
/Users/timothee/git_clone/nim/Nim/lib/system/sysio.nim(80) checkErr
/Users/timothee/git_clone/nim/Nim/lib/system/sysio.nim(72) raiseEIO
/Users/timothee/git_clone/nim/Nim/lib/system.nim(2970) sysFatal
Error: unhandled exception: Unknown IO Error [IOError]
Process 98697 exited with status = 1 (0x00000001)
(lldb) ^D

import osproc

proc test=
  echo "ok1b.1"
  let temp = "brew --version".execCmdEx()
  echo "ok1b.2"
  echo temp
test()

I'm on OSX
(note: can't use gdb because of https://stackoverflow.com/questions/52529838/gdb-8-2-cant-recognized-executable-file-on-macos-mojave-10-14)

that's very annoying because it makes it impossible to debug some programs, in case they're calling execCmdEx somewhere

[Araq]

So ... submit a bug report to your debugger?

[timotheecour]

it works fine in C++ so the issue is how it's done in Nim, it seems to me

#include <cstdio>
#include <iostream>
#include <memory>
#include <stdexcept>
#include <string>
#include <array>

std::string exec(const char* cmd) {
    std::array<char, 128> buffer;
    std::string result;
    std::shared_ptr<FILE> pipe(popen(cmd, "r"), pclose);
    if (!pipe) throw std::runtime_error("popen() failed!");
    while (!feof(pipe.get())) {
        if (fgets(buffer.data(), 128, pipe.get()) != nullptr)
            result += buffer.data();
    }
    return result;
}

int main(){
  auto ret = exec("date");
  std::cout << "ret:" << ret << std::endl;
}

lldb /tmp/D20181107T193702
(lldb) target create "/tmp/D20181107T193702"
Current executable set to '/tmp/D20181107T193702' (x86_64).
(lldb) r
Process 65884 launched: '/tmp/D20181107T193702' (x86_64)
ret:Wed Nov  7 20:44:33 PST 2018

Process 65884 exited with status = 0 (0x00000000)
(lldb)

[krux02]

lldb is not officially supported, only gdb.

[timotheecour]

• unfortunately gdb doesn't work on OSX on latest OS (mojave), as I mentioned above link

I just tried on ubuntu 18.10 to see what works and what doesn't, here's the results:

• ubuntu 18.10:

  • it works with gdb
  • it works with lldb (installed via sudo apt-get install lldb or even via brew install llvm --with-lldb, both being at lldb version 7.0.0)

• OSX (latest, Mojave: 10.14)

  • gdb itself doesn't work
  • it crashes with lldb (as shown above)

so there's currently no way to debug on latest OSX a Nim program that involves a call to execCmdEx :(

/cc @krux02 @Araq
or anyone, if you have an older version of OSX, would you mind trying with gdb on OSX to see if it crashes (as with lldb) or not? so as to isolate what the problem is; thanks!

[timotheecour]

update:

• I used macincloud to try on previous version of OSX (high sierra, 10.13.6); instead of latest (Mojave)
  unfortunately I can't codesign since instructions to codesign require rebooting with recovery mode and that seems impossible on macincloud (see https://gist.github.com/danisfermi/17d6c0078a2fd4c6ee818c954d2de13c#gistcomment-2773820), but a workaround was to use sudo gdb instead of gdb)
  it turns out it also throws for both lldb (illdb-1000.0.38.2) and gdb (which I had to backport to 8.0.1 according to https://stackoverflow.com/questions/49222683/how-do-i-install-gdb-on-macos-10-13-3-high-sierra)

• then I finally managed to make gdb work on OSX on Mojave and patched homebrew formula for it:
  brew install https://raw.githubusercontent.com/timotheecour/homebrew-timutil/master/gdb_tim.rb

/cc @Araq @krux02
the result is that gdb also throws, so the bug is not specific to lldb, it's on both (lldb and gdb) on OSX

[alaviss]

Can you try compiling your example with -d:useFork?