Fix detection of unknown gcc function attributes #8483
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As described in autoconf-archive upstream [1], from where `build/ax_gcc_func_attribute.m4` is forked, the old unknown func attr detection method would throw a false negative anytime an unrelated warning was raised. This results in `ax_cv_have_func_attribute_target` being set to `no` whenever certain compiler Warning flags are switched on. Namely, having `-Wall` on, which is a default CFLAG for some linux distributions, will result in ``` warning: ‘bar’ declared ‘static’ but never defined [-Wunused-function] ``` when evaluating support for the `target` function attribute. With that configuration value set to `no`, the compiled php binaries will not support x86_64 v3 instructions such as avx2 and sse2, which should speed up specific tasks ran by PHP. This issue was originally reported in Ubuntu [2]. [1] http://git.savannah.gnu.org/gitweb/?p=autoconf-archive.git;a=commitdiff;h=df0894ad1a8195df67a52108b931e07d708cec9a [2] https://bugs.launchpad.net/ubuntu/+source/php8.1/+bug/1882279
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Thank you for the PR, and the thorough explanation!
Ugh, that is bad. I think this PR should target the PHP-8.0 branch, and we may consider to update all autoconf files copyied from upstream to the latest revisions for the master branch. |
I based it in the php-8.0 branch but forgot to target it in this PR. Fixed. Should I go ahead and update the other macros in this PR or would it be OK to file another PR for that matter? |
Please submit a separate PR for this, and target the "master" branch. This very PR is about fixing a bug; the full update might cause issues for the stable branches. |
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Thank you ! |
GCC outputs a warning when Wstrict-prototypes is on, in such case the attribute detection always fails even if the attribute is actually supported. This change checks for the "-Wattributes" warning in conftest.err instead of the existence of the file. Bug-Ubuntu: https://bugs.launchpad.net/ubuntu/+source/php8.1/+bug/1882279 Forwarded: php/php-src#8483 Origin: http://git.savannah.gnu.org/gitweb/?p=autoconf-archive.git;a=commitdiff;h=df0894ad1a8195df67a52108b931e07d708cec9a Last-Update: 2022-05-02 Gbp-Pq: Name 0046-Update-gcc-func-attr-macro.patch
As described in autoconf-archive upstream [1], from where
build/ax_gcc_func_attribute.m4is forked, the old unknown func attrdetection method would throw a false negative anytime an unrelated
warning was raised.
This results in
ax_cv_have_func_attribute_targetbeing set tonowhenever certain compiler Warning flags are switched on. Namely, having
-Wallon, which is a default CFLAG for some linux distributions, willresult in
when evaluating support for the
targetfunction attribute.With that configuration value set to
no, the compiled php binarieswill not support x86_64 v3 instructions such as avx2 and sse2, which
should speed up specific tasks ran by PHP.
This issue was originally reported in Ubuntu [2].
[1] http://git.savannah.gnu.org/gitweb/?p=autoconf-archive.git;a=commitdiff;h=df0894ad1a8195df67a52108b931e07d708cec9a
[2] https://bugs.launchpad.net/ubuntu/+source/php8.1/+bug/1882279