From: Geert Fannes <Geert.Fannes@...>
Date: 2005-03-10T00:37:35+09:00
Subject: x86_64 segmentation fault due to forgotten extern directive

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Hello, I have been tracking down a segmentation fault that only appeared
on a x86_64 64 bit linux machine and was finally able to catch the
bastard. I'm not sure it is a bug (it looks more like bad coding
practice from my side), but it might be interesting for other people
experiencing the same problems.

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I created a toy example that shows the essence: I have a ruby program
(test.rb) that calls a C function "cf_test" which was added to the class
String. This C function is defined in test.c and calls another C
function (localFunction) that is contained in another .c file (test2.c)
and thus also in another object file (test2.o). Finally, "compile"
contains the compilation instructions I used for compiling all this.

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Ruby generates a segmentation fault when I omit the "extern" directive
on line 2 of test.c. I guess it is bad practice to omit this, but I got
no errors when I compiled test.c or linked test.o and test2.o together
to generate the shared object file test.so. For some strange reason,
this does not cause any problems on a 32 bit machine, I only found out
about it when I tried to port everything to a x86_64 machine

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I hope this can be useful for someone,

Greetings,

Geert.

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***test.rb***

require './test.so'

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a=3D'abc'.cf_test

puts a.class

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***test.c***

#include "ruby.h"

extern VALUE localFunction(char*);//THIS IS A CRITICAL LINE ON x86_64

VALUE f_test(VALUE self)

{

  return localFunction(RSTRING(self)->ptr);

}

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VALUE cString;

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void Init_test()

{

  cString=3Drb_define_class("String",rb_cObject);

  rb_define_method(cString,"cf_test",f_test,0);

}

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***test2.c***

#include "ruby.h"

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VALUE localFunction(char *pch)

{

  return rb_str_new2(pch);

}

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***compile***

#!/bin/bash

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gcc -fpic -c test2.c -I/usr/local/lib/ruby/1.9/x86_64-linux

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gcc -fpic -c test.c -I/usr/local/lib/ruby/1.9/x86_64-linux

gcc -shared test.o test2.o -o test.so

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