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I want to compile part of my code only on x86 and x86_64 linux, but not s390 linux or others. How to use the macro define in C to achieve it? I know linux is to determine linux OS, and 386, 486 and 586 to determine CPU architecture. Is there an easy macro define to determine x86 linux and x86_64 linux? Thanks
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If gcc -v shows GCC was configured with a --with-arch option (or --with-arch-32 and/or --with-arch-64 ) then that's what will be the default. Without a --with-arch option (and if there isn't a custom specs file in use) then the arch used will be the default for the target.
Compile 32-bit program on 64-bit gcc in C and C++Nowadays the compiler comes with default 64-bit version. Sometimes we need to compile and execute a code into some 32bit system. In that time, we have to use thisS feature. At first, we Shave to check the current target version of the gcc compiler.
Remember that EIP is the instruction pointer or program counter of 32 bit processes and RIP is the instruction pointer or program counter of 64 bit processes.
You can detect whether or not you are in a 64 bit mode easily:
#if defined(__x86_64__)
/* 64 bit detected */
#endif
#if defined(__i386__)
/* 32 bit x86 detected */
#endif
If your compiler does not provide pre-defined macros and constants, you may define it yourself: gcc -D WHATEVER_YOU_WANT.
Additional reward: if you compile your code for, say, amd64, but you don't define amd64, you can compare the results (the version which use amd64-specific parts vs the generic version) and see, whether your amd64 optimalization worths the effort.
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