# CFLAGS/CXXFLAGS bug with configure **URL:** \ **Category:** Development\ **Tags:** development\ **Created:** [May 29, 2019, 5:23pm UTC](https://community.zeek.org/t/cflags-cxxflags-bug-with-configure/5713 "2019-05-29T17:23:32Z")\ **Posts on this page:** 4\ **Page:** 1
**Author:** ![Jim\_Mellander](https://avatars.discourse-cdn.com/v4/letter/j/e47c2d/32.png) [@Jim\_Mellander](https://community.zeek.org/u/Jim_Mellander)\ **Post date:** [May 29, 2019, 5:23pm UTC](https://community.zeek.org/t/cflags-cxxflags-bug-with-configure/5713/1 "2019-05-29T17:23:32Z")
Hi all: I’ve been tinkering with optimizing zeek for performance, and came across a problem with CFLAGS/CXXFLAGS specified to the configure script. Lets say I want to try the -O3 flag for more aggressive optimization than the default -O2: $ CFLAGS=’-O3’ CXXFLAGS=’-O3’ ./configure … ====================| Bro Build Summary |===================== … CFLAGS: -O3 -Wall -Wno-unused -O2 -g -DNDEBUG … CXXFLAGS: -O3 -Wall -Wno-unused -std=c++11 -O2 -g -DNDEBUG … ---
**Author:** ![Jon\_Siwek](https://avatars.discourse-cdn.com/v4/letter/j/71c47a/32.png) [@Jon\_Siwek](https://community.zeek.org/u/Jon_Siwek)\ **Post date:** [May 29, 2019, 9:21pm UTC](https://community.zeek.org/t/cflags-cxxflags-bug-with-configure/5713/2 "2019-05-29T21:21:22Z")
The couple places where we set CMAKE\_C{XX}\_FLAGS don't seem to matter: the flags associated with CMAKE\_BUILD\_TYPE always come last in the generated Makefile and I think that's just what CMake does, not something we can control. However, you should be able to bypass CMake from inserting build-type flags entirely if you supply an unknown/bogus build type:     CFLAGS='-O3' CXXFLAGS='-O3' ./configure --build-type=none - Jon ---
**Author:** ![Jim\_Mellander](https://avatars.discourse-cdn.com/v4/letter/j/e47c2d/32.png) [@Jim\_Mellander](https://community.zeek.org/u/Jim_Mellander)\ **Post date:** [May 30, 2019, 5:04pm UTC](https://community.zeek.org/t/cflags-cxxflags-bug-with-configure/5713/3 "2019-05-30T17:04:27Z")
Thanks, sounds like a CMake bug, or at least a violation of the Principle of Least Surprise - explicit settings are always expected to override defaults… In any event, in the Zeek context, this thread should suffice to document this (admittedly obscure) issue, and mitigation. ---
**Author:** ![system](https://canada1.discourse-cdn.com/flex011/uploads/zeek/original/1X/f09d732bc2cc7c7cc7e35db67cf4e1d5233ce7a7.png) [@system](https://community.zeek.org/u/system)\ **Post date:** [May 6, 2022, 3:46pm UTC](https://community.zeek.org/t/cflags-cxxflags-bug-with-configure/5713/4 "2022-05-06T15:46:32Z")