有些时候我们在编写代码或者阅读开源项目时经常会遇到一些陌生的宏定义，在找遍所有源代码都没发现其在哪里被定义过，这时这些宏定义很可能是系统编译器自己定义的。

root@freedom-u540:~# gcc -v
Using built-in specs.
COLLECT_GCC=gcc
COLLECT_LTO_WRAPPER=/usr/libexec/gcc/riscv64-oe-linux/11.2.0/lto-wrapper
Target: riscv64-oe-linux
Configured with: ../../../../../../work-shared/gcc-11.2.0-r0/gcc-11.2.0/configure --build=x86_64-linux --host=riscv64-oe-linux --target=riscv64-oe-linux --prefix=/usr --exec_prefix=/usr --bindir=/usr/bin --sbindir=/usr/sbin --libexecdir=/usr/libexec --datadir=/usr/share --sysconfdir=/etc --sharedstatedir=/com --localstatedir=/var --libdir=/usr/lib --includedir=/usr/include --oldincludedir=/usr/include --infodir=/usr/share/info --mandir=/usr/share/man --disable-silent-rules --disable-dependency-tracking --with-libtool-sysroot=/ --with-gnu-ld --enable-shared --enable-languages=c,c++,fortran --enable-threads=posix --enable-multilib --enable-default-pie --enable-c99 --enable-long-long --enable-symvers=gnu --enable-libstdcxx-pch --program-prefix=riscv64-oe-linux- --without-local-prefix --disable-install-libiberty --disable-libssp --enable-libitm --enable-lto --disable-bootstrap --with-system-zlib --with-linker-hash-style=gnu --enable-linker-build-id --with-ppl=no --with-cloog=no --enable-checking=release --enable-cheaders=c_global --without-isl --with-build-sysroot=/ --enable-standard-branch-protection --enable-nls --with-glibc-version=2.28 --enable-initfini-array --enable-__cxa_atexit
Thread model: posix
Supported LTO compression algorithms: zlib
gcc version 11.2.0 (GCC)

 宏定义如下：

 gcc -posix -E -dM - </dev/null

 

#define __riscv 1
#define __DBL_MIN_EXP__ (-1021)
#define __riscv_atomic 1
#define __UINT_LEAST16_MAX__ 0xffff
#define __ATOMIC_ACQUIRE 2
#define __FLT128_MAX_10_EXP__ 4932
#define __FLT_MIN__ 1.17549435082228750796873653722224568e-38F
#define __GCC_IEC_559_COMPLEX 2
#define __UINT_LEAST8_TYPE__ unsigned char
#define __INTMAX_C(c) c ## L
#define __CHAR_BIT__ 8
#define __UINT8_MAX__ 0xff
#define __WINT_MAX__ 0xffffffffU
#define __riscv_cmodel_medany 1
#define __FLT32_MIN_EXP__ (-125)
#define __ORDER_LITTLE_ENDIAN__ 1234
#define __SIZE_MAX__ 0xffffffffffffffffUL
#define __WCHAR_MAX__ 0x7fffffff
#define __GCC_HAVE_SYNC_COMPARE_AND_SWAP_4 1
#define __DBL_DENORM_MIN__ ((double)4.94065645841246544176568792868221372e-324L)
#define __GCC_HAVE_SYNC_COMPARE_AND_SWAP_8 1
#define __GCC_ATOMIC_CHAR_LOCK_FREE 1
#define __GCC_IEC_559 2
#define __FLT32X_DECIMAL_DIG__ 17
#define __FLT_EVAL_METHOD__ 0
#define __FLT64_DECIMAL_DIG__ 17
#define __GCC_ATOMIC_CHAR32_T_LOCK_FREE 2
#define __UINT_FAST64_MAX__ 0xffffffffffffffffUL
#define __SIG_ATOMIC_TYPE__ int
#define __DBL_MIN_10_EXP__ (-307)
#define __FINITE_MATH_ONLY__ 0
#define __FLT32X_MAX_EXP__ 1024
#define __GNUC_PATCHLEVEL__ 0
#define __FLT32_HAS_DENORM__ 1
#define __UINT_FAST8_MAX__ 0xff
#define __FLT32_MAX_10_EXP__ 38
#define __INT8_C(c) c
#define __INT_LEAST8_WIDTH__ 8
#define __UINT_LEAST64_MAX__ 0xffffffffffffffffUL
#define __SHRT_MAX__ 0x7fff
#define __LDBL_MAX__ 1.18973149535723176508575932662800702e+4932L
#define __FLT64X_MAX_10_EXP__ 4932
#define __LDBL_IS_IEC_60559__ 2
#define __FLT64X_HAS_QUIET_NAN__ 1
#define __UINT_LEAST8_MAX__ 0xff
#define __GCC_ATOMIC_BOOL_LOCK_FREE 1
#define __FLT128_DENORM_MIN__ 6.47517511943802511092443895822764655e-4966F128
#define __UINTMAX_TYPE__ long unsigned int
#define __linux 1
#define __FLT_EVAL_METHOD_TS_18661_3__ 0
#define __CHAR_UNSIGNED__ 1
#define __UINT32_MAX__ 0xffffffffU
#define __riscv_fdiv 1
#define __LDBL_MAX_EXP__ 16384
#define __FLT128_MIN_EXP__ (-16381)
#define __WINT_MIN__ 0U
#define __FLT128_MIN_10_EXP__ (-4931)
#define __FLT32X_IS_IEC_60559__ 2
#define __INT_LEAST16_WIDTH__ 16
#define __SCHAR_MAX__ 0x7f
#define __FLT128_MANT_DIG__ 113
#define __WCHAR_MIN__ (-__WCHAR_MAX__ - 1)
#define __INT64_C(c) c ## L
#define __GCC_ATOMIC_POINTER_LOCK_FREE 2
#define __SIZEOF_INT__ 4
#define __FLT32X_MANT_DIG__ 53
#define __USER_LABEL_PREFIX__ 
#define __FLT64X_EPSILON__ 1.92592994438723585305597794258492732e-34F64x
#define __STDC_HOSTED__ 1
#define __DBL_DIG__ 15
#define __FLT32_DIG__ 6
#define __FLT_EPSILON__ 1.19209289550781250000000000000000000e-7F
#define __SHRT_WIDTH__ 16
#define __FLT32_IS_IEC_60559__ 2
#define __LDBL_MIN__ 3.36210314311209350626267781732175260e-4932L
#define __STDC_UTF_16__ 1
#define __DBL_IS_IEC_60559__ 2
#define __FLT64X_DENORM_MIN__ 6.47517511943802511092443895822764655e-4966F64x
#define __FP_FAST_FMA 1
#define __FLT32X_HAS_INFINITY__ 1
#define __INT32_MAX__ 0x7fffffff
#define __unix__ 1
#define __INT_WIDTH__ 32
#define __SIZEOF_LONG__ 8
#define __STDC_IEC_559__ 1
#define __STDC_ISO_10646__ 201706L
#define __UINT16_C(c) c
#define __DECIMAL_DIG__ 36
#define __STDC_IEC_559_COMPLEX__ 1
#define __FLT64_EPSILON__ 2.22044604925031308084726333618164062e-16F64
#define __gnu_linux__ 1
#define __FLT128_IS_IEC_60559__ 2
#define __FLT64X_MIN_10_EXP__ (-4931)
#define __LDBL_HAS_QUIET_NAN__ 1
#define __FLT64_MANT_DIG__ 53
#define __FLT64X_MANT_DIG__ 113
#define __GNUC__ 11
#define __pie__ 2
#define __FLT_HAS_DENORM__ 1
#define __SIZEOF_LONG_DOUBLE__ 16
#define __BIGGEST_ALIGNMENT__ 16
#define __FLT64_MAX_10_EXP__ 308
#define __DBL_MAX__ ((double)1.79769313486231570814527423731704357e+308L)
#define __riscv_float_abi_double 1
#define __INT_FAST32_MAX__ 0x7fffffffffffffffL
#define __DBL_HAS_INFINITY__ 1
#define __INTPTR_WIDTH__ 64
#define __FLT64X_HAS_INFINITY__ 1
#define __UINT_LEAST32_MAX__ 0xffffffffU
#define __FLT32X_HAS_DENORM__ 1
#define __INT_FAST16_TYPE__ long int
#define __LDBL_HAS_DENORM__ 1
#define __FLT128_HAS_INFINITY__ 1
#define __DBL_MAX_EXP__ 1024
#define __WCHAR_WIDTH__ 32
#define __FLT32_MAX__ 3.40282346638528859811704183484516925e+38F32
#define __GCC_ATOMIC_LONG_LOCK_FREE 2
#define __PTRDIFF_MAX__ 0x7fffffffffffffffL
#define __FLT32_HAS_QUIET_NAN__ 1
#define __LONG_LONG_MAX__ 0x7fffffffffffffffLL
#define __SIZEOF_SIZE_T__ 8
#define __FLT64X_MIN_EXP__ (-16381)
#define __SIZEOF_WINT_T__ 4
#define __LONG_LONG_WIDTH__ 64
#define __FLT32_MAX_EXP__ 128
#define __GXX_ABI_VERSION 1016
#define __FLT_MIN_EXP__ (-125)
#define __INT16_MAX__ 0x7fff
#define __INT_FAST64_TYPE__ long int
#define __FP_FAST_FMAF 1
#define __FLT128_NORM_MAX__ 1.18973149535723176508575932662800702e+4932F128
#define __FLT64_DENORM_MIN__ 4.94065645841246544176568792868221372e-324F64
#define __DBL_MIN__ ((double)2.22507385850720138309023271733240406e-308L)
#define __FLT64X_NORM_MAX__ 1.18973149535723176508575932662800702e+4932F64x
#define __SIZEOF_POINTER__ 8
#define __LP64__ 1
#define __DBL_HAS_QUIET_NAN__ 1
#define __FLT32X_EPSILON__ 2.22044604925031308084726333618164062e-16F32x
#define __FLT64_MIN_EXP__ (-1021)
#define __FLT64_MIN_10_EXP__ (-307)
#define __riscv_mul 1
#define __FLT64X_DECIMAL_DIG__ 36
#define __REGISTER_PREFIX__ 
#define __UINT16_MAX__ 0xffff
#define __DBL_HAS_DENORM__ 1
#define __FLT32_MIN__ 1.17549435082228750796873653722224568e-38F32
#define __UINT8_TYPE__ unsigned char
#define __FLT_DIG__ 6
#define __NO_INLINE__ 1
#define __DEC_EVAL_METHOD__ 2
#define __FLT_MANT_DIG__ 24
#define __LDBL_DECIMAL_DIG__ 36
#define __VERSION__ "11.2.0"
#define __UINT64_C(c) c ## UL
#define _STDC_PREDEF_H 1
#define __INT_LEAST32_MAX__ 0x7fffffff
#define __GCC_ATOMIC_INT_LOCK_FREE 2
#define __FLT128_MAX_EXP__ 16384
#define __FLT32_MANT_DIG__ 24
#define __FLOAT_WORD_ORDER__ __ORDER_LITTLE_ENDIAN__
#define __FLT128_HAS_DENORM__ 1
#define __FLT128_DIG__ 33
#define __SCHAR_WIDTH__ 8
#define __INT32_C(c) c
#define __ORDER_PDP_ENDIAN__ 3412
#define __riscv_muldiv 1
#define __INT_FAST32_TYPE__ long int
#define __UINT_LEAST16_TYPE__ short unsigned int
#define unix 1
#define __SIZE_TYPE__ long unsigned int
#define __UINT64_MAX__ 0xffffffffffffffffUL
#define __FLT_IS_IEC_60559__ 2
#define __riscv_xlen 64
#define __GNUC_WIDE_EXECUTION_CHARSET_NAME "UTF-32LE"
#define __FLT64X_DIG__ 33
#define __INT8_TYPE__ signed char
#define __ELF__ 1
#define __FLT_RADIX__ 2
#define __INT_LEAST16_TYPE__ short int
#define __LDBL_EPSILON__ 1.92592994438723585305597794258492732e-34L
#define __UINTMAX_C(c) c ## UL
#define __FLT32X_MIN__ 2.22507385850720138309023271733240406e-308F32x
#define __SIG_ATOMIC_MAX__ 0x7fffffff
#define __GCC_ATOMIC_WCHAR_T_LOCK_FREE 2
#define __SIZEOF_PTRDIFF_T__ 8
#define __riscv_fsqrt 1
#define __LDBL_DIG__ 33
#define __FLT64_IS_IEC_60559__ 2
#define __FLT32X_MIN_EXP__ (-1021)
#define __INT_FAST16_MAX__ 0x7fffffffffffffffL
#define __FLT64_DIG__ 15
#define __UINT_FAST32_MAX__ 0xffffffffffffffffUL
#define __UINT_LEAST64_TYPE__ long unsigned int
#define __FLT_HAS_QUIET_NAN__ 1
#define __FLT_MAX_10_EXP__ 38
#define __LONG_MAX__ 0x7fffffffffffffffL
#define __FLT64X_HAS_DENORM__ 1
#define __FLT_HAS_INFINITY__ 1
#define __GNUC_EXECUTION_CHARSET_NAME "UTF-8"
#define __unix 1
#define __UINT_FAST16_TYPE__ long unsigned int
#define __INT_FAST32_WIDTH__ 64
#define __CHAR16_TYPE__ short unsigned int
#define __PRAGMA_REDEFINE_EXTNAME 1
#define __SIZE_WIDTH__ 64
#define __INT_LEAST16_MAX__ 0x7fff
#define __INT64_MAX__ 0x7fffffffffffffffL
#define __FLT32_DENORM_MIN__ 1.40129846432481707092372958328991613e-45F32
#define __SIG_ATOMIC_WIDTH__ 32
#define __INT_LEAST64_TYPE__ long int
#define __INT16_TYPE__ short int
#define __INT_LEAST8_TYPE__ signed char
#define __STDC_VERSION__ 201710L
#define __INT_FAST8_MAX__ 0x7f
#define __FLT128_MAX__ 1.18973149535723176508575932662800702e+4932F128
#define __INTPTR_MAX__ 0x7fffffffffffffffL
#define linux 1
#define __FLT64_HAS_QUIET_NAN__ 1
#define __FLT32_MIN_10_EXP__ (-37)
#define __FLT32X_DIG__ 15
#define __PTRDIFF_WIDTH__ 64
#define __LDBL_MANT_DIG__ 113
#define __riscv_m 2000000
#define __FLT64_HAS_INFINITY__ 1
#define __FLT64X_MAX__ 1.18973149535723176508575932662800702e+4932F64x
#define __SIG_ATOMIC_MIN__ (-__SIG_ATOMIC_MAX__ - 1)
#define __INTPTR_TYPE__ long int
#define __UINT16_TYPE__ short unsigned int
#define __WCHAR_TYPE__ int
#define __SIZEOF_FLOAT__ 4
#define __pic__ 2
#define __UINTPTR_MAX__ 0xffffffffffffffffUL
#define __INT_FAST64_WIDTH__ 64
#define __FLT32_DECIMAL_DIG__ 9
#define __INT_FAST64_MAX__ 0x7fffffffffffffffL
#define __GCC_ATOMIC_TEST_AND_SET_TRUEVAL 1
#define __FLT_NORM_MAX__ 3.40282346638528859811704183484516925e+38F
#define __FLT32_HAS_INFINITY__ 1
#define __FLT64X_MAX_EXP__ 16384
#define __UINT_FAST64_TYPE__ long unsigned int
#define __riscv_a 2000000
#define __riscv_c 2000000
#define __riscv_d 2000000
#define __riscv_f 2000000
#define __riscv_i 2000000
#define __INT_MAX__ 0x7fffffff
#define __riscv_zicsr 2000000
#define __INT64_TYPE__ long int
#define __FLT_MAX_EXP__ 128
#define __ORDER_BIG_ENDIAN__ 4321
#define __DBL_MANT_DIG__ 53
#define __INT_LEAST64_MAX__ 0x7fffffffffffffffL
#define __GCC_ATOMIC_CHAR16_T_LOCK_FREE 1
#define __FP_FAST_FMAF32 1
#define __WINT_TYPE__ unsigned int
#define __UINT_LEAST32_TYPE__ unsigned int
#define __SIZEOF_SHORT__ 2
#define __FLT32_NORM_MAX__ 3.40282346638528859811704183484516925e+38F32
#define __LDBL_MIN_EXP__ (-16381)
#define __riscv_compressed 1
#define __FLT64_MAX__ 1.79769313486231570814527423731704357e+308F64
#define __WINT_WIDTH__ 32
#define __FP_FAST_FMAF64 1
#define __INT_LEAST8_MAX__ 0x7f
#define __INT_LEAST64_WIDTH__ 64
#define __FLT32X_MAX_10_EXP__ 308
#define __SIZEOF_INT128__ 16
#define __FLT64X_IS_IEC_60559__ 2
#define __LDBL_MAX_10_EXP__ 4932
#define __ATOMIC_RELAXED 0
#define __DBL_EPSILON__ ((double)2.22044604925031308084726333618164062e-16L)
#define __FLT128_MIN__ 3.36210314311209350626267781732175260e-4932F128
#define _LP64 1
#define __UINT8_C(c) c
#define __FLT64_MAX_EXP__ 1024
#define __INT_LEAST32_TYPE__ int
#define __SIZEOF_WCHAR_T__ 4
#define __UINT64_TYPE__ long unsigned int
#define __FLT64_NORM_MAX__ 1.79769313486231570814527423731704357e+308F64
#define __FLT128_HAS_QUIET_NAN__ 1
#define __INTMAX_MAX__ 0x7fffffffffffffffL
#define __INT_FAST8_TYPE__ signed char
#define __FLT64X_MIN__ 3.36210314311209350626267781732175260e-4932F64x
#define __LDBL_HAS_INFINITY__ 1
#define __GNUC_STDC_INLINE__ 1
#define __FLT64_HAS_DENORM__ 1
#define __FLT32_EPSILON__ 1.19209289550781250000000000000000000e-7F32
#define __FP_FAST_FMAF32x 1
#define __DBL_DECIMAL_DIG__ 17
#define __STDC_UTF_32__ 1
#define __INT_FAST8_WIDTH__ 8
#define __FLT32X_MAX__ 1.79769313486231570814527423731704357e+308F32x
#define __DBL_NORM_MAX__ ((double)1.79769313486231570814527423731704357e+308L)
#define __BYTE_ORDER__ __ORDER_LITTLE_ENDIAN__
#define __INTMAX_WIDTH__ 64
#define __riscv_flen 64
#define __UINT32_C(c) c ## U
#define __riscv_arch_test 1
#define __FLT_DENORM_MIN__ 1.40129846432481707092372958328991613e-45F
#define __INT8_MAX__ 0x7f
#define __LONG_WIDTH__ 64
#define __PIC__ 2
#define __UINT_FAST32_TYPE__ long unsigned int
#define __FLT32X_NORM_MAX__ 1.79769313486231570814527423731704357e+308F32x
#define __CHAR32_TYPE__ unsigned int
#define __FLT_MAX__ 3.40282346638528859811704183484516925e+38F
#define __INT32_TYPE__ int
#define __SIZEOF_DOUBLE__ 8
#define __FLT_MIN_10_EXP__ (-37)
#define __FLT64_MIN__ 2.22507385850720138309023271733240406e-308F64
#define __INT_LEAST32_WIDTH__ 32
#define __INTMAX_TYPE__ long int
#define __FLT32X_HAS_QUIET_NAN__ 1
#define __ATOMIC_CONSUME 1
#define __GNUC_MINOR__ 2
#define __INT_FAST16_WIDTH__ 64
#define __UINTMAX_MAX__ 0xffffffffffffffffUL
#define __PIE__ 2
#define __FLT32X_DENORM_MIN__ 4.94065645841246544176568792868221372e-324F32x
#define __DBL_MAX_10_EXP__ 308
#define __LDBL_DENORM_MIN__ 6.47517511943802511092443895822764655e-4966L
#define __INT16_C(c) c
#define __STDC__ 1
#define __PTRDIFF_TYPE__ long int
#define __riscv_div 1
#define __ATOMIC_SEQ_CST 5
#define __riscv_zifencei 2000000
#define __UINT32_TYPE__ unsigned int
#define __FLT32X_MIN_10_EXP__ (-307)
#define __UINTPTR_TYPE__ long unsigned int
#define __linux__ 1
#define __LDBL_MIN_10_EXP__ (-4931)
#define __FLT128_EPSILON__ 1.92592994438723585305597794258492732e-34F128
#define __SIZEOF_LONG_LONG__ 8
#define __FLT128_DECIMAL_DIG__ 36
#define __GCC_ATOMIC_LLONG_LOCK_FREE 2
#define __riscv_cmodel_pic 1
#define __FLT_DECIMAL_DIG__ 9
#define __UINT_FAST16_MAX__ 0xffffffffffffffffUL
#define __LDBL_NORM_MAX__ 1.18973149535723176508575932662800702e+4932L
#define __GCC_ATOMIC_SHORT_LOCK_FREE 1
#define __UINT_FAST8_TYPE__ unsigned char
#define __ATOMIC_ACQ_REL 4
#define __ATOMIC_RELEASE 3

 

重要的几个：

#define linux 1

#define __riscv_flen 64

#define __riscv 1

特别是关于CPU架构的定义，如果不从这里看，根本不知道gcc到底是如何定义，在代码中有的写的是 __riscv__， 有的写的是 __RISCV64__，其实都不是在gcc里面定义的，可能是别的什么地方定义的。 是不标准的写法。

 

如果代码中用到了glibc的头文件，比如 emp.h，里面引用stdio.h,即可用gcc查看 GLIBC定义的宏：

如em.h文件

#include <stdio.h>

查看宏定义：

gcc -E -dM emp.h > mcc.txt

可以看到，里面多了许多GLIBC的宏

#define __glibc_macro_warning(message) __glibc_macro_warning1 (GCC warning message)
#define __GLIBC__ 2
#define __GLIBC_PREREQ(maj,min) ((__GLIBC__ << 16) + __GLIBC_MINOR__ >= ((maj) << 16) + (min))