Pete Shanahan's Weblog

AMD64 - compilation flag differences from cc to gcc

Well I've been asked more than once for this, so I decided that a publicly accessible version would help people.

Purpose	sun cc	gnu cc
Compile in 64bit mode	-xarch=<sparcv9|amd64> (-xarch=generic64 soon)	-m64 (gcc really wins here!)
Compile a kernel module	-D_KERNEL	-D_KERNEL -mcmodel=kernel
Multi-Threaded	-D_REENTRANT (stop using -mt in S10)	-D_REENTRANT
Optimization	-xO<0-5>	-O<0-5>
Warnings	-v	-W or -Wall (mini lint)
Warnings are errors	-errwarn=%all	-Werror
Build a shared object (.so)	-G	-shared
Accept C++ style comments	-xCC	None (does it automatically)
Position independent code	-K PIC (32bit addresses - longer sparc instructions) -K pic (not 32bit addresses)	-fpic

There are a few coding gotchas - string constants in gcc get into the .text segment of the application, not the data segment, thus you are not permitted to alter them. Occasionally I find that the final link step of gcc fails with relocation errors - the code segment ends up addressing > 32bit values within itself, by adding -fpic to the compilation flags it works just fine (it's been the occasional test with char foo[MAX_LONG>>1]; in the global segment causing this). September 03, 2004 02:49 PM IST Permalink