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Segmentation Fault when trying to call zend_new_array.

php.internals

Ivan Zanev

6 years ago

Hello,

I'm trying to learn a bit more about HashTable in PHP internally and how
memory is allocated when generating arrays with various sizes. I created a
simple C script that would call

HashTable *ht = zend_new_array(15);

However, when I compile the script with gcc, I get segmentation fault; gdb
tells that the problem is located within _emalloc_56, specifically:

2535 if (UNEXPECTED(AG(mm_heap)->use_custom_heap)) {

That's how I compiled the script:
gcc -I./Zend -I. -I./TSRM -I./main Zend/*.c TSRM/TSRM.c test.c -ldl -lm -g

For the configuration I used:
./configure

Could you please guide me in the right direction? Is there something I
should do before calling zend_new_array?

Sincerely,
Ivan

Unnamed Person

6 years ago

On Tue, Aug 25, 2020 at 5:31 AM Ivan Zanev <ivanzanev477@gmail.com> wrote:

>
> Hello,
>
> I'm trying to learn a bit more about HashTable in PHP internally and how
> memory is allocated when generating arrays with various sizes. I created a
> simple C script that would call
>
> HashTable *ht = zend_new_array(15);
>
> However, when I compile the script with gcc, I get segmentation fault; gdb
> tells that the problem is located within _emalloc_56, specifically:
>
> 2535 if (UNEXPECTED(AG(mm_heap)->use_custom_heap)) {
>
> That's how I compiled the script:
> gcc -I./Zend -I. -I./TSRM -I./main Zend/*.c TSRM/TSRM.c test.c -ldl -lm -g
>
> For the configuration I used:
> ./configure
>
> Could you please guide me in the right direction? Is there something I
> should do before calling zend_new_array?
>
> Sincerely,
> Ivan

Does `test.c` include a main? If so you probably want to use the embed
SAPI. If not then you probably want to build it as an extension.

Ivan Zanev

6 years ago

Yes, it does.

I recompiled php now with

--configure --enable-embed=static

and wrote a simple script:

#include <stdlib.h>
#include <stdio.h>

#include "sapi/embed/php_embed.h"

int main(int argc, char *argv[]) {
php_embed_init(argc, argv);

HashTable *ht = zend_new_array(15);

return 0;
}

Compiled with the following command:

gcc -I./Zend -I. -I./TSRM -I./main Zend/*.c TSRM/TSRM.c test-embed.c -ldl
-lm -lphp7 -g

The segmentation fault problem still occurs, when calling  php_embed_init.

Not sure if that's a problem of libphp7.so which I installed via apt or it
is something related to a missing piece in the test-embed.c script I wrote?

On Tue, Aug 25, 2020 at 2:39 PM Levi Morrison <levi.morrison@datadoghq.com>
wrote:

Alex Dowad

6 years ago

Dear Ivan,

Some suggestions:

- Build your own copy of the PHP embed library using ./configure
--enable-embed=shared or ./configure --enable-embed=static. Link against
that.
- If it doesn't work, get some already-working sample code for use of the
PHP embed SAPI and modify it rather than starting from scratch.
- If you are still struggling, run your test under gdb so you can get a
stack trace when it segfaults. It's as simple as "gdb --args <CLI
invocation here>". Make sure that both the PHP embed SAPI and your own test
code were compiled with debug info enabled.

Alex



On Wed, Aug 26, 2020 at 9:29 AM Ivan Zanev <ivanzanev477@gmail.com> wrote:

Ivan Zanev

6 years ago

Thank you!

On Wed, Aug 26, 2020 at 11:00 AM Alex <alexinbeijing@gmail.com> wrote: