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 -Wcast-qual \
                     -Wundef -Wno-pointer-sign ${FORMAT_EXTENSIONS} \
                     -Wmissing-include-dirs -fdiagnostics-show-option \
                    -Wno-unknown-pragmas \
                    ${CWARNEXTRA}
    #
    # 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-error=constant-conversion
    NO_WSHIFT_COUNT_NEGATIVE=       -Wno-shift-count-negative
    NO_WSHIFT_COUNT_OVERFLOW=       -Wno-shift-count-overflow
    NO_WSELF_ASSIGN=                -Wno-self-assign
    NO_WUNNEEDED_INTERNAL_DECL=     -Wno-error=unneeded-internal-declaration
    NO_WSOMETIMES_UNINITIALIZED=    -Wno-error=sometimes-uninitialized
    NO_WCAST_QUAL=                  -Wno-error=cast-qual
    NO_WTAUTOLOGICAL_POINTER_COMPARE= -Wno-tautological-pointer-compare
    .if ${COMPILER_VERSION} >= 100000
    NO_WMISLEADING_INDENTATION=     -Wno-misleading-indentation
    .endif
    .if ${COMPILER_VERSION} >= 130000
    NO_WUNUSED_BUT_SET_VARIABLE=    -Wno-unused-but-set-variable
    .endif
    .if ${COMPILER_VERSION} >= 140000
    NO_WBITWISE_INSTEAD_OF_LOGICAL= -Wno-bitwise-instead-of-logical
    .endif
    .if ${COMPILER_VERSION} >= 150000
    NO_WSTRICT_PROTOTYPES=          -Wno-strict-prototypes
    .endif
    # 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 \
                    -Wno-error=pointer-sign
    .if ${COMPILER_VERSION} >= 30700
    CWARNEXTRA+=    -Wno-error=shift-negative-value
    .endif
    .if ${COMPILER_VERSION} >= 40000
    CWARNEXTRA+=    -Wno-address-of-packed-member
    .endif
    .if ${COMPILER_VERSION} >= 130000
    CWARNFLAGS+=    -Wno-error=unused-but-set-variable
    .endif
    .endif  # clang
    
    .if ${COMPILER_TYPE} == "gcc"
    .if ${COMPILER_VERSION} >= 40800
    # Catch-all for all the things that are in our tree, but for which we're
    # not yet ready for this compiler.
    NO_WUNUSED_BUT_SET_VARIABLE = -Wno-unused-but-set-variable
    CWARNEXTRA?=    -Wno-error=address                              \
                    -Wno-error=aggressive-loop-optimizations        \
                    -Wno-error=array-bounds                         \
                    -Wno-error=attributes                           \
                    -Wno-error=cast-qual                            \
                    -Wno-error=enum-compare                         \
                    -Wno-error=inline                               \
                    -Wno-error=maybe-uninitialized                  \
                    -Wno-error=overflow                             \
                    -Wno-error=sequence-point                       \
                    -Wno-error=unused-but-set-variable
    .if ${COMPILER_VERSION} >= 60100
    CWARNEXTRA+=    -Wno-error=misleading-indentation               \
                    -Wno-error=nonnull-compare                      \
                    -Wno-error=shift-overflow                       \
                    -Wno-error=tautological-compare
    .endif
    .if ${COMPILER_VERSION} >= 70200
    CWARNEXTRA+=    -Wno-error=memset-elt-size
    .endif
    .if ${COMPILER_VERSION} >= 80000
    CWARNEXTRA+=    -Wno-error=packed-not-aligned
    .endif
    .else
    # For gcc 4.2, eliminate the too-often-wrong warnings about uninitialized vars.
    CWARNEXTRA?=    -Wno-uninitialized
    # GCC 4.2 doesn't have -Wno-error=cast-qual, so just disable the warning for
    # the few files that are already known to generate cast-qual warnings.
    NO_WCAST_QUAL= -Wno-cast-qual
    .endif
    .endif
    
    # This warning is utter nonsense
    CWARNFLAGS+=    -Wno-format-zero-length
    
    # 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"
   FORMAT_EXTENSIONS=      -Wno-format
   .elif ${COMPILER_TYPE} == "clang" && ${COMPILER_VERSION} >= 30600
   FORMAT_EXTENSIONS=      -D__printf__=__freebsd_kprintf__
   .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"
   CFLAGS.gcc+=    -mno-align-long-strings -mpreferred-stack-boundary=2
   CFLAGS.clang+=  -mno-aes -mno-avx
   CFLAGS+=        -mno-mmx -mno-sse -msoft-float
   INLINE_LIMIT?=  8000
   .endif
   
   .if ${MACHINE_CPUARCH} == "arm"
   INLINE_LIMIT?=  8000
   .endif
   
   .if ${MACHINE_CPUARCH} == "aarch64"
   # We generally don't want fpu instructions in the kernel.
   CFLAGS += -mgeneral-regs-only
   # Reserve x18 for pcpu data
   CFLAGS += -ffixed-x18
   INLINE_LIMIT?=  8000
   .endif
   
   #
   # For RISC-V we specify the soft-float ABI (lp64) to avoid the use of floating
   # point registers within the kernel. We also specify the "medium" code model,
   # which generates code suitable for a 2GiB addressing range located at any
   # offset, allowing modules to be located anywhere in the 64-bit address space.
   # Note that clang and GCC refer to this code model as "medium" and "medany"
   # respectively.
   #
   .if ${MACHINE_CPUARCH} == "riscv"
   CFLAGS+=        -march=rv64imafdc -mabi=lp64
   CFLAGS.clang+=  -mcmodel=medium
   CFLAGS.gcc+=    -mcmodel=medany
   INLINE_LIMIT?=  8000
   
   .if ${LINKER_FEATURES:Mriscv-relaxations} == ""
   CFLAGS+=        -mno-relax
   .endif
   .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"
   CFLAGS.clang+=  -mcmodel=large -fno-dwarf2-cfi-asm
   CFLAGS.gcc+=    -mcmodel=medany -msoft-float
   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"
   CFLAGS.clang+=  -mno-aes -mno-avx
   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+=        -mno-altivec -msoft-float
   INLINE_LIMIT?=  15000
   .endif
   
   .if ${MACHINE_ARCH} == "powerpcspe"
   CFLAGS.gcc+=    -mno-spe
   .endif
   
   #
   # Use dot symbols (or, better, the V2 ELF ABI) on powerpc64 to make
   # DDB happy. ELFv2, if available, has some other efficiency benefits.
   #
   .if ${MACHINE_ARCH} == "powerpc64"
   .if ${COMPILER_VERSION} >= 40900
   CFLAGS.gcc+=    -mabi=elfv2
   .else
   CFLAGS.gcc+=    -mcall-aixdesc
   .endif
   CFLAGS.clang+=  -mabi=elfv2
   .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
   
   #
   # The C standard leaves signed integer overflow behavior undefined.
   # gcc and clang opimizers take advantage of this.  The kernel makes
   # use of signed integer wraparound mechanics so we need the compiler
   # to treat it as a wraparound and not take shortcuts.
   #
   CFLAGS+=        -fwrapv
   
   #
   # GCC SSP support
   #
   .if ${MK_SSP} != "no" && \
       ${MACHINE_CPUARCH} != "arm" && ${MACHINE_CPUARCH} != "mips"
   CFLAGS+=        -fstack-protector
   .endif
   
   #
   # Retpoline speculative execution vulnerability mitigation (CVE-2017-5715)
   #
   .if defined(COMPILER_FEATURES) && ${COMPILER_FEATURES:Mretpoline} != "" && \
       ${MK_KERNEL_RETPOLINE} != "no"
   CFLAGS+=        -mretpoline
   .endif
   
   #
   # Add -gdwarf-2 when compiling -g. The default starting in clang v3.4
   # and gcc 4.8 is to generate DWARF version 4. However, our tools don't
   # cope well with DWARF 4, so force it to genereate DWARF2, which they
   # understand. Do this unconditionally as it is harmless when not needed,
   # but critical for these newer versions.
   #
   .if ${CFLAGS:M-g} != "" && ${CFLAGS:M-gdwarf*} == ""
   CFLAGS+=        -gdwarf-2
   .endif
   
   CFLAGS+= ${CWARNFLAGS:M*} ${CWARNFLAGS.${.IMPSRC:T}}
   CFLAGS+= ${CFLAGS.${COMPILER_TYPE}} ${CFLAGS.${.IMPSRC:T}}
   
   # Tell bmake not to mistake standard targets for things to be searched for
   # or expect to ever be up-to-date.
   PHONY_NOTMAIN = afterdepend afterinstall all beforedepend beforeinstall \
                   beforelinking build build-tools buildfiles buildincludes \
                   checkdpadd clean cleandepend cleandir cleanobj configure \
                   depend distclean distribute exe \
                   html includes install installfiles installincludes \
                   obj objlink objs objwarn \
                   realinstall regress \
                   tags whereobj
   
   .PHONY: ${PHONY_NOTMAIN}
   .NOTMAIN: ${PHONY_NOTMAIN}
   
   CSTD=           c99
   
   .if ${CSTD} == "k&r"
   CFLAGS+=        -traditional
   .elif ${CSTD} == "c89" || ${CSTD} == "c90"
   CFLAGS+=        -std=iso9899:1990
   .elif ${CSTD} == "c94" || ${CSTD} == "c95"
   CFLAGS+=        -std=iso9899:199409
   .elif ${CSTD} == "c99"
   CFLAGS+=        -std=iso9899:1999
   .else # CSTD
   CFLAGS+=        -std=${CSTD}
   .endif # CSTD
   
   # Set target-specific linker emulation name.
   LD_EMULATION_aarch64=aarch64elf
   LD_EMULATION_amd64=elf_x86_64_fbsd
   LD_EMULATION_arm=armelf_fbsd
   LD_EMULATION_armv6=armelf_fbsd
   LD_EMULATION_armv7=armelf_fbsd
   LD_EMULATION_i386=elf_i386_fbsd
   LD_EMULATION_mips= elf32btsmip_fbsd
   LD_EMULATION_mipshf= elf32btsmip_fbsd
   LD_EMULATION_mips64= elf64btsmip_fbsd
   LD_EMULATION_mips64hf= elf64btsmip_fbsd
   LD_EMULATION_mipsel= elf32ltsmip_fbsd
   LD_EMULATION_mipselhf= elf32ltsmip_fbsd
   LD_EMULATION_mips64el= elf64ltsmip_fbsd
   LD_EMULATION_mips64elhf= elf64ltsmip_fbsd
   LD_EMULATION_mipsn32= elf32btsmipn32_fbsd
   LD_EMULATION_mipsn32el= elf32btsmipn32_fbsd   # I don't think this is a thing that works
   LD_EMULATION_powerpc= elf32ppc_fbsd
   LD_EMULATION_powerpcspe= elf32ppc_fbsd
   LD_EMULATION_powerpc64= elf64ppc_fbsd
   LD_EMULATION_riscv64= elf64lriscv
   LD_EMULATION_sparc64= elf64_sparc_fbsd
   LD_EMULATION=${LD_EMULATION_${MACHINE_ARCH}}

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