[jira] [Created] (THRIFT-2182) segfault in regression tests (GC bug in rb_thrift_memory_buffer_write)

["Paul Brannan (JIRA)" <ji...@apache.org>]

Paul Brannan created THRIFT-2182:
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             Summary: segfault in regression tests (GC bug in rb_thrift_memory_buffer_write)
                 Key: THRIFT-2182
                 URL: https://issues.apache.org/jira/browse/THRIFT-2182
             Project: Thrift
          Issue Type: Bug
          Components: Ruby - Library
    Affects Versions: 0.9.1, 0.9.2
            Reporter: Paul Brannan


This bug causes the regression tests to segfault on my machine.  As this is a GC bug, it may or may not be easily reproducible.

The rb_thrift_memory_buffer_write function looks like this:

    VALUE rb_thrift_memory_buffer_write(VALUE self, VALUE str) {
      VALUE buf = GET_BUF(self);
      str = force_binary_encoding(str);
      rb_str_buf_cat(buf, RSTRING_PTR(str), RSTRING_LEN(str));
      return Qnil;
    }

When gcc compiles this, it optimizes away the value of str (it is no longer used after RSTRING_PTR(str) and RSTRING_LEN(str) are computed).  Later, rb_str_buf_cat invokes the GC, and the string referenced by str is collected, because there are no references to it on the stack.

Some possible solutions:
* Use StringValuePtr instead of RSTRING_PTR (in general RSTRING_PTR should be avoided in favor of StringValuePtr or StringValueCStr); I believe this will also fix #THRIFT-1047
* Use rb_str_cat instead of rb_str_buf_cat
* Use RB_GC_GUARD to prevent str from getting collected

It appears a similar bug may exist with buffer_value in rb_thrift_memory_buffer_read_into_buffer, and possibly in any of the other 30 places that RSTRING_PTR is used.


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