On Thu, Aug 1, 2024 at 4:01 PM Ilija Tovilo <tovilo.il...@gmail.com> wrote:
> Hi everyone
>
> We've gotten a bug report about compile errors in the PHP 8.4 alpha on
> old C99 compilers (and on some modern compilers when passing the
> -std=c99 flag). Specifically, C99 does not support typedef
> redeclarations, which is a C11 feature.
>
> ```c
> // some_header.h
> typedef struct _zval_struct zval;
> void some_func(zval *zv);
>
> // zend_types.h
> struct _zval_struct { ... };
> typedef struct _zval_struct zval;
> ```
>
> Some headers might want to forward declare zval so that zend_types.h
> doesn't have to be included. The two primary reasons you might want to
> avoid that are 1. to reduce compile times if the header is very large
> and 2. to prevent recursive header dependencies.
>
> However, in C99 this code is actually illegal if both of these headers
> end up being included, because redeclarations of typedefs are not
> allowed. To fix it, the typedef must be removed and the signatures
> must refer to the struct directly.
>
> ```c
> // some_header.h
> struct _zval_struct;
> void some_func(struct _zval_struct *zv);
> ```
>
> I started fixing these in a PR [1] which required more changes than
> expected. After a short discourse, we were wondering whether it might
> be better to switch to a newer C standard instead. Our coding
> standards [2] currently specify that compiling php-src requires C99.
> The Unix installation page on php.net [3] claims it is ANSI C, which
> is certainly outdated. There have been suggestions to require C11 for
> a while, which should be well supported by all compilers shipped with
> maintained distributions.
>
> GCC gained support for C11 in 4.7 [4], LLVM Clang in 3.1, both
> released in 2012. For context, Debian Bullseye comes with GCC 10.2
> [5], Ubuntu Focal Fossa comes with GCC 9.3 [6], RHEL 8 comes with GCC
> 8.x [7]. The biggest blocker in the past was MSVC, which has finally
> added C11 support in Visual Studio 2019 [8]. Technically, Visual
> Studio 2015 and 2017 are still supported by Microsoft [9], but
> according to Christoph they are no longer used for PHP builds since
> version 8.
>
> Hence, it seems like it would be ok to bump our C compiler requirement
> to C11. We'd like to make this change before beta 1 if there are no
> objections. There are no immediate plans to make non-optional use of
> other C11 features, although that is conceivable at some point.
>
> Another benefit brought up by Christoph is that C11 relegated the
> requirement for the compiler to support VLAs (variable-length arrays)
> which was never implemented by MSVC, technically not complying with
> the currently required standard.
>
> If you do have any concerns, please let me know.
>
> Ilija
>
> [1] https://github.com/php/php-src/pull/15079
> [2] [
> https://github.com/php/php-src/blob/8b6f14a9a221599b076e4bc3570f013a7e65aa21/CODING_STANDARDS.md?plain=1#L12](https://github.com/php/php-src/blob/8b6f14a9a221599b076e4bc3570f013a7e65aa21/CODING_STANDARDS.md?plain=1#L12)
> [3] https://www.php.net/manual/en/install.unix.php
> [4] https://stackoverflow.com/a/16256596
> [5] https://packages.debian.org/bullseye/gcc
> [6] https://packages.ubuntu.com/focal/gcc
> [7] https://access.redhat.com/solutions/19458
> [8]
> https://devblogs.microsoft.com/cppblog/c11-and-c17-standard-support-arriving-in-msvc/
> [9]
> https://learn.microsoft.com/en-us/visualstudio/productinfo/vs-servicing
Would now be a good time to consider switching to cmake? Peter(petk) has a
cmake build system on his github that just needs to be touched up.
