FreeBSD/Linux Kernel Cross Reference
sys/conf/kern.mk

     # $FreeBSD: releng/5.0/sys/conf/kern.mk 105019 2002-10-13 02:52:22Z marcel $
     
     #
     # Warning flags for compiling the kernel and components of the kernel.
     #
     # Note that the newly added -Wcast-qual is responsible for generating 
     # most of the remaining warnings.  Warnings introduced with -Wall will
     # also pop up, but are easier to fix.
     CWARNFLAGS?=    -Wall -Wredundant-decls -Wnested-externs -Wstrict-prototypes \
                    -Wmissing-prototypes -Wpointer-arith -Winline -Wcast-qual \
                    -fformat-extensions -ansi
    #
    # The following flags are next up for working on:
    #       -W
    
    #
    # On the i386, do not align the stack to 16-byte boundaries.  Otherwise GCC
    # 2.95 adds code to the entry and exit point of every function to align the
    # stack to 16-byte boundaries -- thus wasting approximately 12 bytes of stack
    # per function call.  While the 16-byte alignment may benefit micro benchmarks, 
    # it is probably an overall loss as it makes the code bigger (less efficient
    # use of code cache tag lines) and uses more stack (less efficient use of data
    # cache tag lines)
    #
    .if ${MACHINE_ARCH} == "i386"
    CFLAGS+=        -mno-align-long-strings -mpreferred-stack-boundary=2
    .endif
    
    #
    # On the alpha, make sure that we don't use floating-point registers and
    # allow the use of BWX etc instructions (only needed for low-level i/o).
    # Also, reserve register t7 to point at per-cpu global variables.
    #
    .if ${MACHINE_ARCH} == "alpha"
    CFLAGS+=        -mno-fp-regs -ffixed-8 -Wa,-mev6
    .endif
    
    #
    # For IA-64, we use r13 for the kernel globals pointer and we only use
    # a very small subset of float registers for integer divides.
    #
    .if ${MACHINE_ARCH} == "ia64"
    CFLAGS+=        -ffixed-r13 -mfixed-range=f32-f127 -mno-sdata
    .endif
    
    #
    # GCC 3.0 and above like to do certain optimizations based on the
    # assumption that the program is linked against libc.  Stop this.
    #
    CFLAGS+=        -ffreestanding

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