How to compile a 32-bit C application using gcc on the 64-bit version of Red Hat Enterprise Linux?

本文介绍如何使用gcc在64位Red Hat Enterprise Linux上编译32位C应用程序，通过添加-m32选项，可以确保整型、长整型和指针变量的大小为32位。同时，需确保链接的库也为32位版本，如glibc、glibc-devel和libgcc等。

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How to compile a 32-bit C application using gcc on the 64-bit version of Red Hat Enterprise Linux?

SOLUTION 已验证 - 已更新 2015年十一月26日19:18 -

English

环境

Red Hat Enterprise Linux (all versions)

问题

How to compile a 32-bit C application using gcc on the 64-bit version of Red Hat Enterprise Linux?

决议

To compile a 32-bit C application for Red Hat Enterprise Linux running on a 64-bit platform, use the gcc option -m32.
- According to the man page for gcc, the -m32 option sets int, long, and pointer variables to 32 bits (4 bytes). The -m64 option sets int to 32 bits (4 bytes) and long & pointer to 64 bits (8 bytes).

The following segment of code demonstrates this:

Raw

#include <stdio.h>

int main()
{
    int i;
    long l;
    char *p;

    printf("Integer size: %i bytes\\n", sizeof(i));
    printf("Long Integer size: %i bytes\\n", sizeof(l));
    printf("Pointer size: %i bytes\\n", sizeof(p));
    return 0;
}

The following is a comparison of the output when compiled with the -m32 and -m64 options:

Raw
```
# gcc -o ./test.64 -m64 test.c
# gcc -o ./test.32 -m32 test.c
#
# ./test.64
Integer size: 4 bytes
Long Integer size: 8 bytes
Pointer size: 8 bytes
#
# ./test.32
Integer size: 4 bytes
Long Integer size: 4 bytes
Pointer size: 4 bytes
```
NOTE: in order to get correct results when compiling applications, make sure that the libraries linked against are installed in 32-bit versions. As an example, the packages glibc, glibc-devel and libgcc are needed for most C applications.
To install the 32-bit versions on Red Hat Enterprise Linux 5 :

Raw
```
# yum install libgcc.i386 glibc.i686 glibc-devel.i386
```

On Red Hat Enterprise Linux 6 and 7 :

Raw

# yum install libgcc.i686 glibc.i686 glibc-devel.i686

On older versions of Red Hat Enterprise Linux the same should be done with up2date:

Raw
```
# up2date --arch=i386 --install glibc-devel libgcc
```