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

     # $FreeBSD$
     
     #
     # Warning flags for compiling the kernel and components of the kernel:
     #
     CWARNFLAGS?=    -Wall -Wredundant-decls -Wnested-externs -Wstrict-prototypes \
                     -Wmissing-prototypes -Wpointer-arith -Winline -Wcast-qual \
                     -Wundef -Wno-pointer-sign ${FORMAT_EXTENSIONS} \
                     -Wmissing-include-dirs -fdiagnostics-show-option \
                    ${CWARNEXTRA}
    MK_CLANG_IS_CC ?= no
    #
    # The following flags are next up for working on:
    #       -Wextra
    
    # Disable a few warnings for clang, since there are several places in the
    # kernel where fixing them is more trouble than it is worth, or where there is
    # a false positive.
    .if ${COMPILER_TYPE} == "clang"
    NO_WCONSTANT_CONVERSION=        -Wno-constant-conversion
    NO_WARRAY_BOUNDS=               -Wno-array-bounds
    NO_WSHIFT_COUNT_NEGATIVE=       -Wno-shift-count-negative
    NO_WSHIFT_COUNT_OVERFLOW=       -Wno-shift-count-overflow
    NO_WUNUSED_VALUE=               -Wno-unused-value
    NO_WSELF_ASSIGN=                -Wno-self-assign
    NO_WFORMAT_SECURITY=            -Wno-format-security
    NO_WUNNEEDED_INTERNAL_DECL=     -Wno-unneeded-internal-declaration
    NO_WSOMETIMES_UNINITIALIZED=    -Wno-error-sometimes-uninitialized
    # Several other warnings which might be useful in some cases, but not severe
    # enough to error out the whole kernel build.  Display them anyway, so there is
    # some incentive to fix them eventually.
    CWARNEXTRA?=    -Wno-error-tautological-compare -Wno-error-empty-body \
                    -Wno-error-parentheses-equality -Wno-error-unused-function \
                    ${NO_WFORMAT}
    .endif
    
    # External compilers may not support our format extensions.  Allow them
    # to be disabled.  WARNING: format checking is disabled in this case.
    .if ${MK_FORMAT_EXTENSIONS} == "no"
    NO_WFORMAT=             -Wno-format
    .else
    FORMAT_EXTENSIONS=      -fformat-extensions
    .endif
    
    #
    # On i386, do not align the stack to 16-byte boundaries.  Otherwise GCC 2.95
    # and above 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).  Explicitly prohibit the use of FPU, SSE and other SIMD
    # operations inside the kernel itself.  These operations are exclusively
    # reserved for user applications.
    #
    # gcc:
    # Setting -mno-mmx implies -mno-3dnow
    # Setting -mno-sse implies -mno-sse2, -mno-sse3 and -mno-ssse3
    #
    # clang:
    # Setting -mno-mmx implies -mno-3dnow and -mno-3dnowa
    # Setting -mno-sse implies -mno-sse2, -mno-sse3, -mno-ssse3, -mno-sse41 and -mno-sse42
    #
    .if ${MACHINE_CPUARCH} == "i386"
    .if ${COMPILER_TYPE} != "clang"
    CFLAGS+=        -mno-align-long-strings -mpreferred-stack-boundary=2
    .else
    CFLAGS+=        -mno-aes -mno-avx
    .endif
    CFLAGS+=        -mno-mmx -mno-sse -msoft-float
    INLINE_LIMIT?=  8000
    .endif
    
    .if ${MACHINE_CPUARCH} == "arm"
    INLINE_LIMIT?=  8000
    .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_CPUARCH} == "ia64"
    CFLAGS+=        -ffixed-r13 -mfixed-range=f32-f127 -fpic #-mno-sdata
    INLINE_LIMIT?=  15000
    .endif
    
    #
    # For sparc64 we want the medany code model so modules may be located
    # anywhere in the 64-bit address space.  We also tell GCC to use floating
    # point emulation.  This avoids using floating point registers for integer
    # operations which it has a tendency to do.
    #
    .if ${MACHINE_CPUARCH} == "sparc64"
    .if ${COMPILER_TYPE} == "clang"
    CFLAGS+=        -mcmodel=large -fno-dwarf2-cfi-asm
    .else
    CFLAGS+=        -mcmodel=medany -msoft-float
    .endif
    INLINE_LIMIT?=  15000
   .endif
   
   #
   # For AMD64, we explicitly prohibit the use of FPU, SSE and other SIMD
   # operations inside the kernel itself.  These operations are exclusively
   # reserved for user applications.
   #
   # gcc:
   # Setting -mno-mmx implies -mno-3dnow
   # Setting -mno-sse implies -mno-sse2, -mno-sse3, -mno-ssse3 and -mfpmath=387
   #
   # clang:
   # Setting -mno-mmx implies -mno-3dnow and -mno-3dnowa
   # Setting -mno-sse implies -mno-sse2, -mno-sse3, -mno-ssse3, -mno-sse41 and -mno-sse42
   # (-mfpmath= is not supported)
   #
   .if ${MACHINE_CPUARCH} == "amd64"
   .if ${COMPILER_TYPE} == "clang"
   CFLAGS+=        -mno-aes -mno-avx
   .endif
   CFLAGS+=        -mcmodel=kernel -mno-red-zone -mno-mmx -mno-sse -msoft-float \
                   -fno-asynchronous-unwind-tables
   INLINE_LIMIT?=  8000
   .endif
   
   #
   # For PowerPC we tell gcc to use floating point emulation.  This avoids using
   # floating point registers for integer operations which it has a tendency to do.
   # Also explicitly disable Altivec instructions inside the kernel.
   #
   .if ${MACHINE_CPUARCH} == "powerpc"
   CFLAGS+=        -msoft-float -mno-altivec
   INLINE_LIMIT?=  15000
   .endif
   
   #
   # Use dot symbols on powerpc64 to make ddb happy
   #
   .if ${MACHINE_ARCH} == "powerpc64"
   CFLAGS+=        -mcall-aixdesc
   .endif
   
   #
   # For MIPS we also tell gcc to use floating point emulation
   #
   .if ${MACHINE_CPUARCH} == "mips"
   CFLAGS+=        -msoft-float
   INLINE_LIMIT?=  8000
   .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
   
   #
   # GCC SSP support
   #
   .if ${MK_SSP} != "no" && ${MACHINE_CPUARCH} != "ia64" && \
       ${MACHINE_CPUARCH} != "arm" && ${MACHINE_CPUARCH} != "mips"
   CFLAGS+=        -fstack-protector
   .endif
   
   #
   # Add -gdwarf-2 when compiling -g
   #
   .if ${COMPILER_TYPE} == "clang" && ${CFLAGS:M-g} != "" && ${CFLAGS:M-gdwarf} == ""
   CFLAGS+=        -gdwarf-2
   .endif

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