Description:
------------
#0  0x00007f9e8c4ba355 raise (libc.so.6 + 0x3c355)
#1  0x00007f9e8c4a3853 abort (libc.so.6 + 0x25853)
#2  0x00007f9e8c4a3727 __assert_fail_base.cold (libc.so.6 + 0x25727)
#3  0x00007f9e8c4b2936 __assert_fail (libc.so.6 + 0x34936)
#4  0x000055e572bcd0d2 __zval_get_string_func (php + 0x64f0d2)
#5  0x000055e572bcd106 zval_get_string_func (php + 0x64f106)
#6  0x00007f9e8a479635 zval_get_tmp_string (curl.so + 0x4635)
#7  0x00007f9e8a482503 build_mime_structure_from_hash (curl.so + 0xd503)
#8  0x00007f9e8a483dfa _php_curl_setopt (curl.so + 0xedfa)
#9  0x00007f9e8a484c4b zif_curl_setopt (curl.so + 0xfc4b)
#10 0x000055e572c4fd71 ZEND_DO_ICALL_SPEC_RETVAL_UNUSED_HANDLER (php + 0x6d1d71)
#11 0x000055e572cb64bc execute_ex (php + 0x7384bc)
#12 0x000055e572cba613 zend_execute (php + 0x73c613)
#13 0x000055e572bdc0e9 zend_execute_scripts (php + 0x65e0e9)
#14 0x000055e572b39fc0 php_execute_script (php + 0x5bbfc0)
#15 0x000055e572cbd1c1 do_cli (php + 0x73f1c1)
#16 0x000055e572cbe3c1 main (php + 0x7403c1)
#17 0x00007f9e8c4a5002 __libc_start_main (libc.so.6 + 0x27002)
#18 0x000055e57277e6ae _start (php + 0x2006ae)

Test script:
---------------
<?php

class x
{
	private $_body;

	public function __construct(SimpleXMLElement $body)
	{
		$this->_body = $body;
	}

	public function __toString()
	{
		return $this->_body->asXML();
	}
}

$body = new x(simplexml_load_string('<?xml version="1.0" encoding="UTF-8"?>
<Test>
    <Id>123</Id>
</Test>'));

$ch = curl_init();

curl_setopt($ch, CURLOPT_POSTFIELDS, $body);

Expected result:
----------------
no segfault - which can be achieved by manually casting to string first eg. curl_setopt($ch, CURLOPT_POSTFIELDS, (string)$body);

Actual result:
--------------
segfault