### Description ping @xkaraman
cmake is overriding distro build flags
Here is typical CFLAGS for EL distros
``` export CFLAGS='-O2 -flto=auto -ffat-lto-objects -fexceptions -g -grecord-gcc-switches -pipe -Wall -Werror=format-security -Wp,-D_FORTIFY_SOURCE=2 -Wp,-D_GLIBCXX_ASSERTIONS -specs=/usr/lib/rpm/redhat/redhat-hardened-cc1 -fstack-protector-strong -specs=/usr/lib/rpm/redhat/redhat-annobin-cc1 -m64 -march=x86-64-v2 -mtune=generic -fasynchronous-unwind-tables -fstack-clash-protection -fcf-protection'
## try to build cd build/ make [ 1%] Building C object src/CMakeFiles/kamailio.dir/lib/srdb1/db_row.c.o In file included from /usr/include/bits/libc-header-start.h:33, from /usr/include/string.h:26, from /home/centos/src/kamailio-5.8/src/lib/srdb1/../../core/str.h:26, from /home/centos/src/kamailio-5.8/src/lib/srdb1/db_con.h:33, from /home/centos/src/kamailio-5.8/src/lib/srdb1/db_val.h:40, from /home/centos/src/kamailio-5.8/src/lib/srdb1/db_row.h:37, from /home/centos/src/kamailio-5.8/src/lib/srdb1/db_row.c:33: /usr/include/features.h:412:4: warning: #warning _FORTIFY_SOURCE requires compiling with optimization (-O) [-Wcpp] 412 | # warning _FORTIFY_SOURCE requires compiling with optimization (-O) ```
It is probably due to `cmake/compiler-specific.cmake`: ``` # If GCC version is greater than 4.2.0, enable the following flags if(CMAKE_C_COMPILER_VERSION VERSION_GREATER 4.2.0) target_compile_options( common INTERFACE -m64 -minline-all-stringops -falign-loops -ftree-vectorize -fno-strict-overflow -mtune=generic ) endif() ```
Packaging for ELx requires respecting the default flags - for EL9 included here for reference ``` CFLAGS='-O2 -flto=auto -ffat-lto-objects -fexceptions -g -grecord-gcc-switches -pipe -Wall -Werror=format-security -Wp,-D_FORTIFY_SOURCE=2 -Wp,-D_GLIBCXX_ASSERTIONS -specs=/usr/lib/rpm/redhat/redhat-hardened-cc1 -fstack-protector-strong -specs=/usr/lib/rpm/redhat/redhat-annobin-cc1 -m64 -march=x86-64-v2 -mtune=generic -fasynchronous-unwind-tables -fstack-clash-protection -fcf-protection' CXXFLAGS='-O2 -flto=auto -ffat-lto-objects -fexceptions -g -grecord-gcc-switches -pipe -Wall -Werror=format-security -Wp,-D_FORTIFY_SOURCE=2 -Wp,-D_GLIBCXX_ASSERTIONS -specs=/usr/lib/rpm/redhat/redhat-hardened-cc1 -fstack-protector-strong -specs=/usr/lib/rpm/redhat/redhat-annobin-cc1 -m64 -march=x86-64-v2 -mtune=generic -fasynchronous-unwind-tables -fstack-clash-protection -fcf-protection' FCFLAGS='-O2 -flto=auto -ffat-lto-objects -fexceptions -g -grecord-gcc-switches -pipe -Wall -Werror=format-security -Wp,-D_FORTIFY_SOURCE=2 -Wp,-D_GLIBCXX_ASSERTIONS -specs=/usr/lib/rpm/redhat/redhat-hardened-cc1 -fstack-protector-strong -specs=/usr/lib/rpm/redhat/redhat-annobin-cc1 -m64 -march=x86-64-v2 -mtune=generic -fasynchronous-unwind-tables -fstack-clash-protection -fcf-protection -I/usr/lib64/gfortran/modules' FFLAGS='-O2 -flto=auto -ffat-lto-objects -fexceptions -g -grecord-gcc-switches -pipe -Wall -Werror=format-security -Wp,-D_FORTIFY_SOURCE=2 -Wp,-D_GLIBCXX_ASSERTIONS -specs=/usr/lib/rpm/redhat/redhat-hardened-cc1 -fstack-protector-strong -specs=/usr/lib/rpm/redhat/redhat-annobin-cc1 -m64 -march=x86-64-v2 -mtune=generic -fasynchronous-unwind-tables -fstack-clash-protection -fcf-protection -I/usr/lib64/gfortran/modules' LDFLAGS='-Wl,-z,relro -Wl,--as-needed -Wl,-z,now -specs=/usr/lib/rpm/redhat/redhat-hardened-ld -specs=/usr/lib/rpm/redhat/redhat-annobin-cc1 ' ```
ELx packaging typically involves this dance:
``` # in practice RPM build tools have macros for all the following steps # use standard distro flags export CFLAGS=.... export CXXFLAGS=... export LDFLAGS=....
./configure ```
Is there a way we can respect distro build flags with cmake?
Suggestion for `cmake/compiler-specific.cmake` - allow user to override CFLAGS/LDFLAGS:
``` if(CMAKE_SYSTEM_PROCESSOR STREQUAL "x86_64")
if(CMAKE_C_COMPILER_ID STREQUAL "GNU") target_compile_definitions(common INTERFACE CC_GCC_LIKE_ASM)
if(NOT DEFINED ENV{CFLAGS}) target_compile_options( common INTERFACE -O0 # <$<$BOOL:${PROFILE}:-pg> )
target_compile_options( common INTERFACE -Wall -funroll-loops -Wcast-align -Werror=implicit-function-declaration -Werror=implicit-int )
# If GCC version is greater than 4.2.0, enable the following flags if(CMAKE_C_COMPILER_VERSION VERSION_GREATER 4.2.0) target_compile_options( common INTERFACE -m64 -minline-all-stringops -falign-loops -ftree-vectorize -fno-strict-overflow -mtune=generic ) endif() endif() elseif(CMAKE_C_COMPILER_ID STREQUAL "Clang") target_compile_definitions(common INTERFACE CC_GCC_LIKE_ASM) if(NOT DEFINED ENV{CFLAGS}) target_compile_options(common INTERFACE -m64) endif() if(NOT DEFINED ENV{LDFLAGS}) target_link_options(common INTERFACE -m64) endif() endif()
# etc etc
```
Hey @space88man,
We had this discussion with @linuxmaniac as well. In https://github.com/kamailio/kamailio/issues/4053#issuecomment-2545146514, you can find a way to provide the `CFLAGS` and the `LDFLAGS`. In [Environment Variables for Languages](https://cmake.org/cmake/help/latest/manual/cmake-env-variables.7.html#id4%7C), you can find all the `ENV` flags that you can pass to `cmake`. These `FLAGS` are respected when called on the **first time** of `cmake` configuration. We can also define/modify [CMAKE_[LANG]_FLAGS](https://cmake.org/cmake/help/latest/variable/CMAKE_LANG_FLAGS.html#variable:...) after the first time config phase.
Note though, this will initialize the `FLAGS` with your provided ones and append to them the project's one found in `target_compile_options`. Is this ok, or do you need to completely override them and only use whatever you provide?
@xkaraman, I definitely want to keep all the `-DHAVE_XXX` flags deduced by the build system; however the compiler options like `-O0 -mtune=generic` need to be completely overridden.
I tried just defining `CFLAGS="-O2 -g …"` but that got appended/prepended (?) to the CFLAGS so RHELs `FORTIFY_SOURCE` preference didn't work - it looks like `-O0` (from current cmake) "won".
Summary: need to keep preprocessor defines, but override compiler options.
@space88man Hmm, i just read through https://gcc.gnu.org/onlinedocs/gcc/Optimize-Options.html. Since, the one you define is passed first (prepended) followed by the project options (each `target_compile_options` appends to the last ones), the last `-O` wins the race.
I think since the default option of GCC is `-O0` if none is passed, I think it's safe to remove it from the `compiler-specific.cmake`, so if one want to alter the optimization level, it's safe to do it via the above `CFLAGS="-O2"` method.
Closed #4082 as completed.
Closed with 5d4002415f.
-
space88man -
Xenofon Karamanos