Tag Archives: segmentation faults

PHP CLI on IBMi PASE Memory Limit Problem (AIX OS via QP2TERM)

I ran into one of the hardest things to figure out the dreaded “Segmentation fault” and “Illegal instruction” while running php-cli in a QP2TERM session (a PASE/AIX/”IBMs unix” shell)The exact errors were:

php-cli[9]: 12345 Illegal instruction (coredump)  –when ran non-interactive

php-cli[9]: 12345 Segmentation fault(coredump) –when ran interactive

Note: php-cli is the shell script that calls the PHP interpreter on line 9 from the command line and 12345 is the AIX process id that had the issue.  Segmentation fault means you are addressing memory outside of your data segment which has a predefined size (256MB). coredump should be a data dump in the system log

In /usr/local/zendsvr/etc/php.ini I tried to increase the
memory_limit = 512M ; Maximum amount of memory a script may consume (512M). 

I tried to set the value in my script with
ini_set(‘memory_limit’, ‘512M’); 

I even tried to set it on the command line with the -d option
/usr/local/zendsvr/bin/php-cli -d memory_limit=512M myscript.php

I figured out the amount of memory my script was using by reducing the number of records it was processing and running the follow echo command to get the peak memory usage:

echo “Memory Peak Usage: “.(memory_get_peak_usage()/1024/1024).” MB”;

The actual memory bottle neck was happening further up the chain at the AIX process/job level.  The default memory limit of AIX process is 256MB with additional Data Segments of 256MB (Hex 0x10000000 2^8) with a max size of 8 additional data segments

Solution

Set the LDR_CNTRL environment variable in the parent process (PHP-CLI) to multiple data segments (in the example below 8 additional data segments of 256MB for 2.25GB of memory [this is the max…]) and then run your php script and then unset the memory limit so you don’t affect other processes.   Modify the shell script /usr/local/zendsvr/bin/php-cli and wrap the call to the php interpreter ($ZCE_PREFIX/bin/php “$@”) with the export and unsetting of LDR_CNTRL as shown below

export LDR_CNTRL=MAXDATA=0xB0000000@DSA
$ZCE_PREFIX/bin/php “$@”
unset LDR_CNTRL

putenv should probably not work because the parent process has to set LDR_CNTRL not the PHP script

putenv(“LDR_CNTRL=MAXDATA=0xB0000000@DSA”);

Use echo getenv(“LDR_CNTRL”); to see what its set to in your PHP script.

If you are using the FASTCGI w/ apache you can modify the config file (/www/zendsvr/conf/fastcgi.conf) and add to the end of  the line starting with Server type=”application/x-httpd-php” …

SetEnv=”LDR_CNTRL=MAXDATA=0xB0000000@DSA”

Caution

If you are hitting this limit you should probably look at the program you created because there may be something that is inefficiently using memory and that should be fixed instead of changing the memory limit.

What is this DSA

“The @DSA which can be appended to this value allows the boundary been private data and shared memory to be changed, allowing more segments to be used and the heap to start in segment 3. It also allows shared objects to be moved into segment 2 to give more contiguous space (See Figure 4).” – http://ibmsystemsmag.com/CMSTemplates/IBMSystemsMag/Print.aspx?path=/aix/administrator/systemsmanagement/Avoiding-Those–Segmentation-Fault–Failure-Messag

More info here: https://www.ibm.com/support/knowledgecenter/en/ssw_aix_61/com.ibm.aix.genprogc/lrg_prg_support.htm

These issues might also go away when we go from 32 bit to 64 bit.

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iSeries Access 64 Bit Driver problems Segmentation Faults

Update: May 17 2016 – At common I found out that 64 bit issues should now all be resolved when using the latest PHP 5.6, the unixODBC manager 2.2.14+ and IBM i Access for Linux ODBC driver.  This was effecting PHP extension: PDO ODBC, and ODBC_* functions

PHP 5.6.x+
http://php.net/downloads.php

UnixODBC Manager
http://www.unixodbc.org/

IBM i Access ODBC Driver [for Linux] (ibm-iaccess-1.1.0.1-1.0.x86_64)
http://www-03.ibm.com/systems/power/software/i/access/linux.html

Kevin Adler’s Article from IBM
https://www.ibm.com/developerworks/ibmi/library/i-ibmi-access-client-solutions-linux/

Segmentation Fault Problem

I’ve had a lot of trouble with using the iSeries Access 64 bit odbc driver for Linux (iSeriesAccess-5.4.0-1.6.x86_64.rpm) on my RHEL linux box to connect toa  V5R4 iSeries server.  I switched back to using the 32 bit driver and saying i’ll wait until they update the 64 bit driver to work.

I was going to the PHP page and finding just a blank screen returned to the browser, which made it a pain to debug.  I found out after looking at the apache error log file in /var/log/httpd/error_log  that there were segmentation faults with the following error:

[notice] child pid XXXXX exit signal Segmentation fault (11)

To try and debug the PHP to see what causing the problem i put die(‘here’) statements in my code until i found out where the interpretor wasn’t getting to because of the seg fault.   I found out on the return of the Zend Framework’s PDO ODBC Fetchall statement the program was causing the seg fault.  I also noticed that this only occured when i had a null field in the DB2 udb for iSeries database.  The field was a char datatype.

If you’re having this problem i’d recommend just installing the 32 bit driver(iSeriesAccess-5.4.0-1.2.i386.rpm).

Debugging

Here’s how i understand requests get called in case you want to try and debug the problem:

  1. Request for page comes in from Apache
  2. PHP runs and makes db calls through  a DSN
  3. All db calls go through unixODBC manager
  4. The db call then goes through the IBM Client Access driver you have specified and executes the sql on the iSeries.
  5. If the driver has a problem with a null field it would create a segmentation fault.

Here’s a link to someone’s explanation of the problems using the 64 bit driver:

https://www.ibm.com/developerworks/forums/thread.jspa?messageID=14510046&#14510046

Need help understanding how to install the driver and setup all the linux files (/etc/odbc.ini /etc/odbcisnt.ini)

Here’s the link to the driver download

iSeries Access Linux Driver download

Remember to edit your
/etc/odbcinst.ini

[iSeries Access ODBC Driver]

Description             = iSeries Access for Linux ODBC Driver
Driver          = /opt/ibm/iSeriesAccess/lib/libcwbodbc.so
Setup           = /opt/ibm/iSeriesAccess/lib/libcwbodbcs.so
NOTE1           = If using unixODBC 2.2.11 or later and you want the 32 and 64-bit ODBC drivers to share DSN's,
NOTE2           = the following Driver64/Setup64 keywords will provide that support.
Driver64                = /opt/ibm/iSeriesAccess/lib64/libcwbodbc.so
Setup64         = /opt/ibm/iSeriesAccess/lib64/libcwbodbcs.so
Threading               = 2
DontDLClose             = 1
UsageCount              = 1

and /etc/odbc.ini

[iSeriesDSN]
Description = iSeries Access ODBC Driver DSN for iSeries
Driver = iSeries Access ODBC Driver
System = iSeriesSystemName
UserID =
Password =
Naming = 0
DefaultLibraries = QGPL
Database =
ConnectionType = 0
CommitMode = 2
ExtendedDynamic = 0
DefaultPkgLibrary = QGPL
DefaultPackage = A/DEFAULT(IBM),2,0,1,0,512
AllowDataCompression = 1
LibraryView = 0
AllowUnsupportedChar = 0
ForceTranslation = 0
Trace = 0

Giving credit to IBM for this example file