Description:
------------
Hi, 
 
we're running PHP 4.3.8 as apache module, Apache runs 
without threads. 
The domxml extension registers an libxml2 generic error 
handler during its initialization. 
We have another apache module, which makes use of libxml2, 
this one doesn't register an error handler. 
 
When then second apache module encounters an XML error, 
apache segfaults 
in the domxml_error function. Here's a backtrace of the 
problem: 
 
#0 ?0x404d3448 in php_apache_sapi_send_headers () 
from ./etc/httpd/modules/libphp4.so 
#1 ?0x4049c84e in sapi_send_headers () 
from ./etc/httpd/modules/libphp4.so 
#2 ?0x4045c456 in php_header () 
from ./etc/httpd/modules/libphp4.so 
#3 ?0x404a7518 in php_ub_body_write () 
from ./etc/httpd/modules/libphp4.so 
#4 ?0x404a63b3 in php_body_write () 
from ./etc/httpd/modules/libphp4.so 
#5 ?0x404952eb in php_printf () 
from ./etc/httpd/modules/libphp4.so 
#6 ?0x40495a4d in php_error_cb () 
from ./etc/httpd/modules/libphp4.so 
#7 ?0x404c165f in zend_error () 
from ./etc/httpd/modules/libphp4.so 
#8 ?0x40495698 in php_verror () 
from ./etc/httpd/modules/libphp4.so 
#9 ?0x4049576f in php_error_docref0 () 
from ./etc/httpd/modules/libphp4.so 
#10 0x403c6951 in domxml_error () 
from ./etc/httpd/modules/libphp4.so 
#11 0x4083cb86 in xmlReportError (err=0x81dc978, 
ctxt=0x81dc7f8, str=0x81e03b0 "Document is empty\n", 
channel=0x403c6910 <domxml_error>, data=0x0) 
? ? at error.c:283 
#12 0x4083ce9a in __xmlRaiseError (schannel=0, 
channel=0x4083d19c <xmlParserError__internal_alias>, 
data=0x81dc7f8, ctx=0x81dc7f8, nod=0x0, domain=1, 
? ? code=4, level=XML_ERR_FATAL, file=0x81df640 "", 
line=1, str1=0x0, str2=0x0, str3=0x0, int1=0, int2=0, 
msg=0x408d5111 "Document is empty\n") 
? ? at error.c:573 
#13 0x4083fef4 in xmlFatalErr (ctxt=0x81dc7f8, 
error=1080649792, info=0x51 <Address 0x51 out of bounds>) 
at parser.c:360 
#14 0x4084fa17 in xmlParseTryOrFinish (ctxt=0x81dc7f8, 
terminate=0) at parser.c:9098 
#15 0x40850358 in xmlParseChunk__internal_alias 
(ctxt=0x81dc7f8, chunk=0x81dc9e4 "????\003", size=228, 
terminate=0) at parser.c:9763 
#16 0x40cd108c in 
xmlpp::DomParser::parse_stream(std::istream&) 
(this=0xbfffeab0, in=@0xbfffecf0) at basic_string.h:781 
 
The problem is domxml's "global" error handler. Even if 
the second module would register an error handler, 
it would override PHP's error handler. IMHO the best 
approach would be to register the error handler 
only during operations calling libxml functions and 
deregister it afterwards. 
The performance overhead should be minimal and it's very 
clean. What do you think? 
 
Cheers, 
Thomas 
 

Actual result:
--------------
See backtrace in description