Completely unnecessary compiler warnings in function ‘from_zval_write_sockaddr_aux’

[VARGA-Peter]

### Description

/bin/sh /builds/php-8.2.4/libtool --silent --preserve-dup-deps --tag CC --mode=compile gcc-12 -Iext/standard/ -I/builds/php-8.2.4/ext/standard/ -I/builds/php-8.2.4/include -I/builds/php-8.2.4/main -I/builds/php-8.2.4 -I/builds/php-8.2.4/ext/date/lib -I/usr/include/libxml2 -I/usr/include/libpng16 -I/builds/php-8.2.4/ext/mbstring/libmbfl -I/builds/php-8.2.4/ext/mbstring/libmbfl/mbfl -I/builds/php-8.2.4/TSRM -I/builds/php-8.2.4/Zend  -D_GNU_SOURCE -D_REENTRANT -pthread  -fno-common -Wformat-truncation -Wlogical-op -Wduplicated-cond -Wno-clobbered -Wall -Wextra -Wno-strict-aliasing -Wno-unused-parameter -Wno-sign-compare -g -O2 -fvisibility=hidden -pthread -Wimplicit-fallthrough=1 -DZTS -DZEND_SIGNALS   -DZEND_ENABLE_STATIC_TSRMLS_CACHE=1 -c /builds/php-8.2.4/ext/standard/link.c -o ext/standard/link.lo  -MMD -MF ext/standard/link.dep -MT ext/standard/link.lo
In function ‘from_zval_write_sockaddr_aux’,
    inlined from ‘from_zval_write_name’ at /builds/php-8.2.4/ext/sockets/conversions.c:1041:2:
/builds/php-8.2.4/ext/sockets/conversions.c:727:9: warning: ‘family’ may be used uninitialized [-Wmaybe-uninitialized]
  727 |         switch (family) {
      |         ^~~~~~
/builds/php-8.2.4/ext/sockets/conversions.c: In function ‘from_zval_write_name’:
/builds/php-8.2.4/ext/sockets/conversions.c:703:25: note: ‘family’ was declared here
  703 |         int             family;
      |                         ^~~~~~ 

/bin/sh /builds/php-8.2.4/libtool --silent --preserve-dup-deps --tag CC --mode=compile gcc-12 -Iext/standard/ -I/builds/php-8.2.4/ext/standard/ -I/builds/php-8.2.4/include -I/builds/php-8.2.4/main -I/builds/php-8.2.4 -I/builds/php-8.2.4/ext/date/lib -I/usr/include/libxml2 -I/usr/include/libpng16 -I/builds/php-8.2.4/ext/mbstring/libmbfl -I/builds/php-8.2.4/ext/mbstring/libmbfl/mbfl -I/builds/php-8.2.4/TSRM -I/builds/php-8.2.4/Zend  -D_GNU_SOURCE -D_REENTRANT -pthread  -fno-common -Wformat-truncation -Wlogical-op -Wduplicated-cond -Wno-clobbered -Wall -Wextra -Wno-strict-aliasing -Wno-unused-parameter -Wno-sign-compare -g -O2 -fvisibility=hidden -pthread -Wimplicit-fallthrough=1 -DZTS -DZEND_SIGNALS   -DZEND_ENABLE_STATIC_TSRMLS_CACHE=1 -c /builds/php-8.2.4/ext/standard/math.c -o ext/standard/math.lo  -MMD -MF ext/standard/math.dep -MT ext/standard/math.lo
/builds/php-8.2.4/ext/sockets/conversions.c: In function ‘from_zval_write_controllen’:
/builds/php-8.2.4/ext/sockets/conversions.c:1122:31: warning: ‘len’ may be used uninitialized [-Wmaybe-uninitialized]
 1122 |         msghdr->msg_control = accounted_emalloc(len, ctx);
      |                               ^~~~~~~~~~~~~~~~~~~~~~~~~~~
/builds/php-8.2.4/ext/sockets/conversions.c:1112:18: note: ‘len’ was declared here
 1112 |         uint32_t len;
      |                  ^~~ 

### PHP Version

PHP 8.2.4

### Operating System

SLES 15.4 with gcc 12

[Girgias]

I'm not hitting those bogus compiler warnings on Fedora 37 and GCC 12.2.1 nor Clang 15. What is the full GCC compiler version you are running?

[VARGA-Peter]

I'm not hitting those bogus compiler warnings on Fedora 37 and GCC 12.2.1 nor Clang 15. What is the full GCC compiler version you are running?

-v options returns this:

Using built-in specs.
COLLECT_GCC=gcc-12
COLLECT_LTO_WRAPPER=/usr/lib64/gcc/x86_64-suse-linux/12/lto-wrapper
OFFLOAD_TARGET_NAMES=nvptx-none
OFFLOAD_TARGET_DEFAULT=1
Target: x86_64-suse-linux
Configured with: ../configure --prefix=/usr --infodir=/usr/share/info --mandir=/usr/share/man --libdir=/usr/lib64 --libexecdir=/usr/lib64 --enable-languages=c,c++,objc,fortran,obj-c++,ada,go,d --enable-offload-targets=nvptx-none, --enable-offload-defaulted --without-cuda-driver --enable-checking=release --disable-werror --with-gxx-include-dir=/usr/include/c++/12 --enable-ssp --disable-libssp --disable-libvtv --enable-cet=auto --disable-libcc1 --disable-plugin --with-bugurl=https://bugs.opensuse.org/ --with-pkgversion='SUSE Linux' --with-slibdir=/lib64 --with-system-zlib --enable-libstdcxx-allocator=new --disable-libstdcxx-pch --enable-libphobos --enable-version-specific-runtime-libs --with-gcc-major-version-only --enable-linker-build-id --enable-linux-futex --enable-gnu-indirect-function --program-suffix=-12 --without-system-libunwind --enable-multilib --with-arch-32=x86-64 --with-tune=generic --build=x86_64-suse-linux --host=x86_64-suse-linux
Thread model: posix
Supported LTO compression algorithms: zlib
gcc version 12.2.1 20220830 [revision e927d1cf141f221c5a32574bde0913307e140984] (SUSE Linux)

[nielsdos]

I think the warnings are true positives.
from_zval_write_int will not write to the pointer on error or an int that's out of the [INT_MIN, INT_MAX] range. In those cases the value will remain uninitialised.

[nielsdos]

I submitted a PR to fix the uninitialized accesses. However, this does not get rid of the compile warnings because now the compiler is just not smart enough to see the variables can no longer be used uninitialized.

[VARGA-Peter]

I submitted a PR to fix the uninitialized accesses. However, this does not get rid of the compile warnings because now the compiler is just not smart enough to see the variables can no longer be used uninitialized.

I understand, but don't you think that just a dummy initialisation - while the declaration - should be done, just to get rid of the warning? It's always good to have no warning even you know the compiler isn't smart enough to analyse the flow correctly?

[nielsdos]

IMO yes we should get rid of the warning, I was already considering that. I also read the review comment on my PR now and proposed a solution for the warning: #10966 (comment).
As far as I understand this is usually only done in master though and not for stable versions.

[VARGA-Peter]

I submitted a PR to fix the uninitialized accesses. However, this does not get rid of the compile warnings because now the compiler is just not smart enough to see the variables can no longer be used uninitialized.

OK, I now checked the function from_zval_write_uint32() and I think it has nothing to do, if the compiler is smart or not. Definitely, as written above, the additional check [if (ctx->err.has_error)] must be done and till now it lead to UB. So the compiler warning revealed this bug.

Now, the situation changed and I don't think that the compiler can see that the added code fixed a bug and now indeed the variable cannot be accessed uninitialised - due to the new check. Maybe gcc 16 is that smart but there remains always the problem that the function is in another file, so the compiler doesn't have enough information. A conditional meta data informing the compiler when the variable is written could solve the problem but this is something for the future...