Compiler Options



  • -Ofast : -O3 + optimizations that are not valid for all standard-compliant programs

  • -march=native : 針對現在的 CPU 做優化,出來的程式不保證在其他 CPU 上會 work
    • 通用於 GCC 和 Clang
  • -flto : Link Time Optimization

  • -m32 : 32 bits

  • -m64 : 64 bits

  • -dumpspecs : 產生 specs file

  • -fPIC : generate position independent code

  • -fpic : generate position independent code
    • platform-dependent
    • may produce smaller code than -fPIC
    • may be a little bit faster
  • -march=native -Q --help=target : 輸出 GCC 在目前機器上使用 -march=native 參數會打開的優化選項
    • -Q --help=target 只適用於 GCC
  • -fdump-tree-original

_FORTIFY_SOURCE (since glibc 2.3.4)
        Defining this macro causes some lightweight checks to be performed to detect some buffer overflow  errors
        when  employing  various  string  and  memory  manipulation functions (for example, memcpy(3), memset(3),
        stpcpy(3),  strcpy(3),  strncpy(3),  strcat(3),   strncat(3),   sprintf(3),   snprintf(3),   vsprintf(3),
        vsnprintf(3), gets(3), and wide character variants thereof).  For some functions, argument consistency is
        checked; for example, a check is made that open(2) has been supplied with a mode argument when the speci‐
        fied flags include O_CREAT.  Not all problems are detected, just some common cases.

        If  _FORTIFY_SOURCE  is  set  to  1,  with compiler optimization level 1 (gcc -O1) and above, checks that
        shouldn't change the behavior of conforming programs are performed.  With _FORTIFY_SOURCE set to 2,  some
        more checking is added, but some conforming programs might fail.

        Some of the checks can be performed at compile time (via macros logic implemented in header files), and
        result in compiler warnings; other checks take place at run time, and result in a run-time error  if  the
        check fails.

        Use of this macro requires compiler support, available with gcc(1) since version 4.0.