zend: introducing ZEND_ELEMENT_COUNT for struct's dynamic arrays.

[devnexen]

It is mostly for ubsan and helping array bound checking.

[nielsdos]

This is a really nice feature that I've seen used in Linux too to prevent bugs. I'm not sure if element_count is actually already implemented (seems like the feature request is open atm), but counted_by is available in Clang.

[devnexen]

yes for gcc it s still in review.

[iluuu1994]

Does this work on structs with the struct hack? (i.e. last_element[1]) We have a few of those, you can search by \*\w+\[1\];, although I'm not sure how many apply.

[devnexen]

I ve tried with zend_type_list locally, seems to work. I ve tried the limit of it, changing to pointers or non integral counters and it fails to compile rightfully for those.

[iluuu1994]

Great, thank you! My regex was sub-optimal for obvious reasons (* requirement). I used another one (\w+\[(0|1)?\];\n\}) and found more candidates:

• zend_ffi_callback_data
• cdf_catalog_t
• zend_jit_trace_stack_frame
• ir_refs
• fpm_scoreboard_s
• phpdbg_file_source
• zend_ast_list
• zend_attribute
• zend_type_list
• zend_string
• zend_property_info_list
• zend_trait_precedence
• zend_inheritance_cache_entry
• zend_call_info

[dstogov]

Looks fine.

[bukka]

It would be good to eventually get rid of the struct hack as well to also make builtin size checks work. Remember reading this article about work that is being done in Linux kernel for that: https://lwn.net/Articles/908817/

[morrisonlevi]

As far as I understand it, using flexible array members is no-go because we support C++ compilers to interpret our headers. C++ still doesn't support flexible array members. So until we have a strategy for that, I don't think we can get rid of the struct hack.