Overriding default flags

[tristanz]

This is likely a question born of ignorance, but is there a way to override the default flags in common.gypi?

I need to compile with RTTI enabled but node-gyp defaults to -fno-rtti. This is required to compile against boost, for instance.

[TooTallNate]

So in case you (or anyone else) is wondering, the "default flags" used when building your addon comes from node's common.gypi file.

As you can see if you scroll through that file -fno-rtti is indeed a default. So in your own gyp file, you must negate that. This involves specifying the cflags with a ! at the end, meaning "not". In the case of -fno-rtti, it's specified in the cflags_cc section, so try adding this:

...
  'cflags_cc!': [ '-fno-rtti' ]
...

Additionally, Mac builds usually have their own section to specify these flags, so you usually have to fix this twice (don't ask me why, gyp just kinda is weird in that case), so for Macs, add this (note that the "xcode_settings" name will vary depending on the flag you are enabling/disabling):

...
  ['OS=="mac"', {
    'xcode_settings': {
      'GCC_ENABLE_CPP_RTTI': 'YES'
    }
  }]
...

That should do it. For completeness sake, this is a barebones gyp file compatible with node-gyp that should have RTTI enabled:

{
  'targets': [
    {
      'target_name': 'bindings',
      'sources': [ 'bindings.cc' ],
      'cflags_cc!': [ '-fno-rtti' ],
      'conditions': [
        ['OS=="mac"', {
          'xcode_settings': {
            'GCC_ENABLE_CPP_RTTI': 'YES'
          }
        }]
      ]
    }
  ]
}

Reopen if that doesn't work for you. Cheers!

[tristanz]

Adding the following seems to solve the issue on OSX:

'conditions': [
  ['OS=="mac"', {
    'xcode_settings': { 'GCC_ENABLE_CPP_RTTI': 'YES' }
  }]
]

I cannot test on linux, but there's a Chromium example that suggests it could be:

[ 'OS=="linux" or OS=="freebsd" or OS=="openbsd" or OS=="solaris"',
  {
    'cflags_cc!': ['-fno-rtti'],
    'cflags_cc+': ['-frtti'],
  }
]

[TooTallNate]

@tristanz That looks correct to me :) Glad you got it figured out.

[tristanz]

Terrific. Thanks!

[tristanz]

I'm still struggling to fix this on Windows. I get an error

 error LNK2001: unresolved external symbol "void __cdecl boost::throw_exception

which seems to stem from an earlier warning:

warning C4530: C++ exception handler used, but unwind semantics are not enabled. Sp
ecify /EHsc

I tried adding the following but it doesn't seem to add /EHsc.

'msvs_settings': {
  'VCCLCompilerTool': {
    'ExceptionHandling': '2',  # /EHsc
  },
}

This is likely more node-gyp ignorance but ideas are appreciated.

[tristanz]

Looks like default settings are different in the Release configuration. The fix is:

      'configurations': {
        'Release': {
          'msvs_settings': {
            'VCCLCompilerTool': {
              'ExceptionHandling': 1,
            }
          }
        }
      },

This seems to have changed multiple times over the last several versions.

[edhemphill]

Does anyone know why -fno-rtti was used as a default? Any particular reason?

[TooTallNate]

@edhemphill node-gyp uses the same configuration as when node itself it built, so the answer is because node itself doesn't need rtti.

[edhemphill]

thanks...

[springmeyer]

I'm hitting this same issue on windows. I'm finding it impossible to override the ExceptionHandling value (which for me like @tristanz breaks my build with linking errors). The only workaround I can find (as mentioned at brianmcd/contextify#45) is to manually modify the common.gypi that node-gyp bundles from node itself.

I'm putting

          'msvs_settings': {
            'VCCLCompilerTool': {
              'ExceptionHandling': 1,
            }
          }

in my binding.gyp, trying both release and debug configurations and 'ExceptionHandling': 0 still ends up in the visual studio output file. I'm on windows 7 with node v0.10.3 and node-gyp v0.9.5 installed globally.

[springmeyer]

ugh... looks like a gyp bug/complexity that may require modifying how node's common.gypi is written: https://groups.google.com/forum/?fromgroups=#!topic/gyp-developer/p98GJxYJuH4

[kirvedx]

Adding /EHsc on Windows...hope it helps - took me a little bit of trial/error and searching around.

Inside of 'target_defaults':

'configurations':
{
  'Debug':
  {
    'defines': [ 'DEBUG', '_DEBUG' ],
    'msvs_settings':
    {
        'VCCLCompilerTool':
        {
            'RuntimeLibrary': 3, # shared debug
            'ExceptionHandling': 1,     # /EHsc  doesn't work.
            '/EHsc' # Enable unwind semantics for Exception Handling.  This one actually does the trick
            # this is also where you can put /GR or /MDd, or other defines.
        }
    }
  },
  'Release':
  {
        'VCCLCompilerTool':
        {
            'RuntimeLibrary': 2, # shared release
            'ExceptionHandling': 1,     # /EHsc  doesn't work.
            '/EHsc' # Enable unwind semantics for Exception Handling.  This one actually does the trick
            # this is also where you can put /GR or /MD, or other defines.
        }
  }
}

Example using node-gyp to build MySQL C++ Connector, overriding defaults. It uses C++ Exception Handler and so as you will see the warning has been suppressed because unwind semantics are now enabled:

EDIT: Closed the code block fence
EDIT 2: Adding why
WHY: Because this issue shows up on Google as #1 for me for a couple of different things I've had to search for...this puts the answers I've found here -> I realize this issue is closed sorry for confusion.