Date: Mon, 12 Aug 2002 09:53:31 +1000 From: Duncan Anker <d.anker@au.darkbluesea.com> To: questions@freebsd.org Subject: Using gcc flag -fno-builtin in kernel compilation Message-ID: <3D56F8FB.1030401@au.darkbluesea.com>
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Hi all, I'm curious about the use of the -fno-builtin flag with regards to building a FreeBSD kernel. According to the GCC man pages, the compiler will normally replace certain calls with inlined/optimized functions at the expense of being able to trace/replace those functions, makin smaller, faster code. Usage of the -fno-builtin flag inhibts the compiler from doing this, forcing it to use the standard libraries. All well and good. However, the kernel LINT file uses -fno-builtin as an example for compiler flag options with the comment "Here we use it to inhibit use of non-optimal gcc builtin functions (e.g., memcmp)." This suggests that gcc's inlining is not optimal - is this the case, or does FreeBSD provide it's own overriding functions for these? The short question is, should I use -fno-builtin in my kernel builds or not? What other flags should I pass to make the kernel more high-performance? I'm currently using -fomit-frame-pointer. Is this useful? Is it worth upping the optimization level from -O to -O2 or -O3? Any tips people can offer would be greatly appreciated. TIA Duncan Anker To Unsubscribe: send mail to majordomo@FreeBSD.org with "unsubscribe freebsd-questions" in the body of the message
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