>> I'm encountering a SIGSEGV in PHP-FPM on PHP 7.4.2 in a Symfony app. The
>> bug seems to happen during the rendering of a Twig template; this makes it
>> hard for me to pinpoint the code that triggers the segfault.
> I'm not sure if I could gather helpful enough info about the issue, but
> anyway I filed a bug here:
>> gdb output for the segfault: (only showing the first 10 entries, it goes on and on for more than 20000 entriesthere may be many more, I gave up after that)
> #0 0x00007f7ea5fdc6d1 in bf_zend_execute () from /usr/lib64/php/modules/blackfire.so
> #1 0x0000560bec0b20c0 in ZEND_DO_FCALL_SPEC_RETVAL_USED_HANDLER () at /usr/src/debug/php-7.4.2-1.fc31.remi.x86_64/Zend/zend_vm_execute.h:1714
> #2 execute_ex (ex=0x7f7e99d6b2c0) at /usr/src/debug/php-7.4.2-1.fc31.remi.x86_64/Zend/zend_vm_execute.h:53821
> #3 0x00007f7ea5fdc6f8 in bf_zend_execute () from /usr/lib64/php/modules/blackfire.so
> #4 0x0000560bec0b20c0 in ZEND_DO_FCALL_SPEC_RETVAL_USED_HANDLER () at /usr/src/debug/php-7.4.2-1.fc31.remi.x86_64/Zend/zend_vm_execute.h:1714
> #5 execute_ex (ex=0x7f7e99d6b2c0) at /usr/src/debug/php-7.4.2-1.fc31.remi.x86_64/Zend/zend_vm_execute.h:53821
The symptoms sounds like you have a global function (each call handled in ZEND_DO_FCALL_SPEC_RETVAL_USED_HANDLER) that's recursively calling itself, infinitely. The stack trace doesn't say which.
When blackfire is used, it seems to use C's call stack, which leads to a stack overflow.
When blackfire is used, the C PHP engine manages a different stack and doesn't recurse, so it doesn't have a stack overflow, and the memory leak would be slower.
Infinite recursion leading to a segfault is **a known bug with no plans to be fixed that I know of,** which I've encountered many times.
You may also want to try running the same code with xdebug - Xdebug will throw/log an error if you recurse more than max_nesting_level(defaults to 100).
That will give you the php function that calls itself.
If you can reproduce the issue consistently, you may also want to look into https://github.com/adsr/phpspy (It has a top-like mode:)