先来看看gcc官方手册吧

These ‘-m’ switches are supported in addition to the above on x86-64 processors in 64-bit environments. -m32 -m64 -mx32 -m16

-miamcu Generate code for a 16-bit, 32-bit or 64-bit environment.

The ‘-m32’ option sets int, long, and pointer types to 32 bits, and generates code that runs on any i386 system. The ‘-m64’ option sets int to 32 bits and long and pointer types to 64 bits, and generates code for the x86-64 architecture. For Darwin only the ‘-m64’ option also turns off the ‘-fno-pic’ and ‘-mdynamic-no-pic’ options.

The ‘-mx32’ option sets int, long, and pointer types to 32 bits, and generates code for the x86-64 architecture.

The ‘-m16’ option is the same as ‘-m32’, except for that it outputs the .code16gcc assembly directive at the beginning of the assembly output so that the binary can run in 16-bit mode.

The ‘-miamcu’ option generates code which conforms to Intel MCU psABI. It requires the ‘-m32’ option to be turned on.

执行编译的程序需要安装32位lib：

$sudo apt-get install lib32ncurses5 lib32z1

编译时需安装multilib：

sudo apt-get install gcc-multilib g++-multilib

在我的电脑上-m32能够运行，-mx32需要内核支持，在编译内核时有mx32的选项，CentOS7内核和GCC都没开启支持mx32，Debian9内核没开启，但gcc支持

下面是elf读取出来的信息：

-mx32：在64位系统中，指针和long都是64位的（此处只讨论linux，Windows不是），因此程序可以使用的内存大小可以远远大于4GiB。但是很多程序并不需要4GiB以上内存，这样内存地址只使用了低4字节造成一定的浪费，而且对于x86的CPU（准确的说是amd64或x86-64，不含IA64），64位数据运算速度远远慢于32位数据，指针和long是32位既浪费了高4字节的空间，又拖累了运行速度，于是有人搞出了指针和long是32位的mx32：你同样可以使用INT64这样的8字节数据，但编译出的程序体积更小，运行速度更快。

$ g++ size.cpp -O3 -mx32 -o size $ readelf -h ./size ELF Header:   Magic:   7f 45 4c 46 01 01 01 00 00 00 00 00 00 00 00 00   Class:                             ELF32  Data:                              2's complement, little endian   Version:                           1 (current)   OS/ABI:                            UNIX - System V   ABI Version:                       0   Type:                              DYN (Shared object file)   Machine:                           Advanced Micro Devices X86-64  Version:                           0x1   Entry point address:               0x7e0   Start of program headers:          52 (bytes into file)   Start of section headers:          6600 (bytes into file)   Flags:                             0x0   Size of this header:               52 (bytes)   Size of program headers:           32 (bytes)   Number of program headers:         9   Size of section headers:           40 (bytes)   Number of section headers:         31   Section header string table index: 30

-m32：编译出来的是32位程序，既可以在32位操作系统运行，又可以在64位操作系统运行。$ g++ size.cpp -O3 -m32 -o size $ readelf -h ./size ELF Header:   Magic:   7f 45 4c 46 01 01 01 00 00 00 00 00 00 00 00 00   Class:                             ELF32  Data:                              2's complement, little endian   Version:                           1 (current)   OS/ABI:                            UNIX - System V   ABI Version:                       0   Type:                              DYN (Shared object file)   Machine:                           Intel 80386  Version:                           0x1   Entry point address:               0x818   Start of program headers:          52 (bytes into file)   Start of section headers:          6668 (bytes into file)   Flags:                             0x0   Size of this header:               52 (bytes)   Size of program headers:           32 (bytes)   Number of program headers:         9   Size of section headers:           40 (bytes)   Number of section headers:         31   Section header string table index: 30

$ g++ size.cpp -O3 -o size $ readelf -h ./size ELF Header:   Magic:   7f 45 4c 46 02 01 01 00 00 00 00 00 00 00 00 00   Class:                             ELF64   Data:                              2's complement, little endian   Version:                           1 (current)   OS/ABI:                            UNIX - System V   ABI Version:                       0   Type:                              DYN (Shared object file)   Machine:                           Advanced Micro Devices X86-64   Version:                           0x1   Entry point address:               0xa60   Start of program headers:          64 (bytes into file)   Start of section headers:          11320 (bytes into file)   Flags:                             0x0   Size of this header:               64 (bytes)   Size of program headers:           56 (bytes)   Number of program headers:         9   Size of section headers:           64 (bytes)   Number of section headers:         31   Section header string table index: 30

-m16，只有在32位的linux上才能使用，同样需要在编译内核时做设置，只有在32位内核中才有该选项，gcc同样也只有32位版本才支持。几乎没人使用，除了某些16位的嵌入式