[Bug] [PHP] build failure with recent compiler

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Apache SkyWalking Component

PHP (apache/skywalking-php)

What happened

When building on Fedora 44 (rust 1.94, llvm 22.1)

   Compiling hyper-timeout v0.5.2
     Running `/usr/bin/rustc --crate-name hyper_timeout --edition=2018 /builddir/build/BUILD/php-pecl-skywalking-agent-1.1.0-build/php-pecl-skywalking-agent-1.1.0/mycargo/hyper-timeout/src/lib.rs --error-format=json --json=diagnostic-rendered-ansi,artifacts,future-incompat --crate-type lib --emit=dep-info,metadata,link -C opt-level=3 -C embed-bitcode=no --check-cfg 'cfg(docsrs,test)' --check-cfg 'cfg(feature, values())' -C metadata=dc4ad138a08c8681 -C extra-filename=-ea9ca08f1f95b231 --out-dir /builddir/build/BUILD/php-pecl-skywalking-agent-1.1.0-build/php-pecl-skywalking-agent-1.1.0/skywalking-php-1.1.0/target/release/deps -C strip=debuginfo -L dependency=/builddir/build/BUILD/php-pecl-skywalking-agent-1.1.0-build/php-pecl-skywalking-agent-1.1.0/skywalking-php-1.1.0/target/release/deps --extern hyper=/builddir/build/BUILD/php-pecl-skywalking-agent-1.1.0-build/php-pecl-skywalking-agent-1.1.0/skywalking-php-1.1.0/target/release/deps/libhyper-b340540417151363.rmeta --extern hyper_util=/builddir/build/BUILD/php-pecl-skywalking-agent-1.1.0-build/php-pecl-skywalking-agent-1.1.0/skywalking-php-1.1.0/target/release/deps/libhyper_util-a9a53a64120ba4f7.rmeta --extern pin_project_lite=/builddir/build/BUILD/php-pecl-skywalking-agent-1.1.0-build/php-pecl-skywalking-agent-1.1.0/skywalking-php-1.1.0/target/release/deps/libpin_project_lite-9ebfd8f9bbd47493.rmeta --extern tokio=/builddir/build/BUILD/php-pecl-skywalking-agent-1.1.0-build/php-pecl-skywalking-agent-1.1.0/skywalking-php-1.1.0/target/release/deps/libtokio-18532e123daf054b.rmeta --extern tower_service=/builddir/build/BUILD/php-pecl-skywalking-agent-1.1.0-build/php-pecl-skywalking-agent-1.1.0/skywalking-php-1.1.0/target/release/deps/libtower_service-0a587eddbcee03aa.rmeta --cap-lints allow -Copt-level=3 -Cdebuginfo=2 -Ccodegen-units=1 -Cstrip=none -Cforce-frame-pointers=yes -Clink-arg=-specs=/usr/lib/rpm/redhat/redhat-package-notes --cap-lints=warn`
error[E0080]: attempt to compute `1_usize - 216_usize`, which would overflow
    --> /builddir/build/BUILD/php-pecl-skywalking-agent-1.1.0-build/php-pecl-skywalking-agent-1.1.0/skywalking-php-1.1.0/target/release/build/phper-sys-0fda0a7263b8ae1d/out/php_bindings.rs:1782:26
     |
1782 |     ["Size of _IO_FILE"][::std::mem::size_of::<_IO_FILE>() - 216usize];
     |                          ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ evaluation of `_` failed here
error[E0080]: attempt to compute `1_usize - 16_usize`, which would overflow
    --> /builddir/build/BUILD/php-pecl-skywalking-agent-1.1.0-build/php-pecl-skywalking-agent-1.1.0/skywalking-php-1.1.0/target/release/build/phper-sys-0fda0a7263b8ae1d/out/php_bindings.rs:1968:30
     |
1968 |     ["Size of _zval_struct"][::std::mem::size_of::<_zval_struct>() - 16usize];
     |                              ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ evaluation of `_` failed here
error[E0080]: attempt to compute `1_usize - 8_usize`, which would overflow
    --> /builddir/build/BUILD/php-pecl-skywalking-agent-1.1.0-build/php-pecl-skywalking-agent-1.1.0/skywalking-php-1.1.0/target/release/build/phper-sys-0fda0a7263b8ae1d/out/php_bindings.rs:2026:34
     |
2026 |     ["Size of _zend_refcounted"][::std::mem::size_of::<_zend_refcounted>() - 8usize];
     |                                  ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ evaluation of `_` failed here
error[E0080]: attempt to compute `1_usize - 32_usize`, which would overflow
    --> /builddir/build/BUILD/php-pecl-skywalking-agent-1.1.0-build/php-pecl-skywalking-agent-1.1.0/skywalking-php-1.1.0/target/release/build/phper-sys-0fda0a7263b8ae1d/out/php_bindings.rs:2036:30
     |
2036 |     ["Size of _zend_string"][::std::mem::size_of::<_zend_string>() - 32usize];
     |                              ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ evaluation of `_` failed here
error[E0080]: attempt to compute `24_usize - 32_usize`, which would overflow

What you expected to happen

No error

How to reproduce

Build on modern distro

Anything else

No response

Are you willing to submit a pull request to fix on your own?

• Yes I am willing to submit a pull request on my own!

Code of Conduct

• I agree to follow this project's Code of Conduct

[jmjoy]

The build fails with a compilation error (E0080) during the phper-sys binding generation. This is caused by a discrepancy in memory layout calculations between the system-default LLVM 22 and the LLVM 21 bundled with Rust 1.94.0.

When bindgen uses the system's LLVM 22 to parse PHP headers, it generates structural layout assertions (size/alignment checks) that the Rust compiler (using its internal LLVM 21) finds inconsistent. This triggers constant evaluation overflows in the generated php_bindings.rs.

Version Context:
Running rustc -V --verbose reveals the internal LLVM version:

rustc 1.94.0 (4a4ef493e 2026-03-02)
binary: rustc
commit-hash: 4a4ef493e3a1488c6e321570238084b38948f6db
commit-date: 2026-03-02
host: x86_64-unknown-linux-gnu
release: 1.94.0
LLVM version: 21.1.8

Since the system Clang/LLVM 22 is ahead of Rust's LLVM 21, they calculate PHP structure sizes differently. We must wait for a newer Rust release that supports LLVM 22 or downgrade the build-time libclang.

Steps to Reproduce / Solution:

To resolve this, force the environment to use LLVM 21 to ensure consistency between bindgen and rustc:

# 1. Install LLVM 21 compatibility libraries
sudo dnf install clang21-devel

# 2. Set environment variables to override defaults
export RUSTUP_TOOLCHAIN=1.94.0
export LIBCLANG_PATH=/usr/lib64/llvm21/lib64

# 3. Re-run the installation
pecl install skywalking_agent