Why does the PHP extension fail to load with _zval_ptr_dtor_wrapper error

I sometimes come across this error when loading an extension in PHP

PHP Warning:  PHP Startup: Unable to load dynamic library
'/usr/lib64/php-zts/5.5/modules/myext.so' -
/usr/lib64/php-zts/5.5/modules/myext.so: undefined symbol:
_zval_ptr_dtor_wrapper in Unknown on line 0

From the Google results it is not very easy to find out what this means.

Technically the extension was compiled with a PHP version using the -enable-debug flag, which wraps all calls to zval_ptr_dtor in a wrapper macro that does not exist in a regular, non-debug build.

But a debug extension and non-debug PHP are incompatible.

PHP extensions are only compatible between different installations if the following constraints are the same for the compiling and the executing PHP binary:

  • OS (Linux, Mac)
  • libc (glibc or musl for Alpine)
  • PHP version up to the minor level (5.5, 5.6, 7.0, 7.1)
  • extension version (20151012 for PHP 7.0)
  • thread-safety (ZTS) or non-thread-safety (NTS)
  • debug or non-debug (--enable-debug flag during compile).
More about: PHPExtension

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