[patch] Cleaning up amd64 kernel optimization options
dim at FreeBSD.org
Thu Dec 22 15:35:48 UTC 2011
I would like to ask some feedback on the attached patch, which cleans up
the kernel optimization options for amd64. This was touched upon
earlier by Alexander Best in freebsd-toolchain, here:
What this patch attempts to fix is the following:
- When you compile amd64 kernels for debug, they still get optimized
with "-O2 -frename-registers", which is almost certain to make
debugging miserable. Optimizing at higher levels makes variables and
code move around, or disappear altogether. About -frename-registers
the gcc documentation even says: "Depending on the debug information
format adopted by the target, however, it can make debugging
impossible, since variables will no longer stay in a “home register”."
- Clang doesn't support the -frename-registers option, so you get
harmless but annoying "warning: argument unused during compilation:
'-frename-registers'" messages during buildkernel.
The patch makes it so that:
- For normal amd64 kernel builds, it uses "-O2 -frename-registers",
unless Clang is used, then it uses plain "-O2".
- For debug amd64 kernel builds, it uses "-O", just like all the other
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