My career as software developer began with embedded programming for 8-bit microprocessor. The main language I used in that time was assembler. Processors changed as assembler changed as well. Later when I started develop Windows implementation in C++ I also used inline assembler instructions in my C++ code, sometime it was necessary for example when naked functions were used. Currently Microsoft Visual Studio does not support inline assembler for 64-bit platform. But g++ compiler does. Here is example of such code:
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#include <stdio.h> int main() { long int sum; __asm__( "movq $0xa, %rax\n" "movq $0xd, %rdx\n" "addq %rax, %rdx\n"); __asm__("movq %%rdx, %0\n":"=r" (sum)); printf("Sum of rax and rdx registers is: %ld\n", sum); return 0; } |
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# g++ -o asm64 asm64.cpp # ./asm64 Sum of rax and rdx registers is: 23 |
The same code without C++ wrapper:
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.global main .text main: movq $0xa, %rax movq $0xd, %rdx addq %rax, %rdx push %rax # save registers push %rcx # printf(format, sum) movq $format, %rdi # format parameter (format) movq %rdx, %rsi # 2-nd parameter – sum xorq %rax, %rax # printf is var args call printf pop %rcx # restore caller-save register pop %rax # exit(0) movq $60, %rax # syscall 60 is exit xorq %rdi, %rdi # return code 0 syscall format: .asciz "Sum of rax and rdx registers is: %ld\n" |
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# g++ att.s -o att # ./att Sum of rax and rdx registers is: 23 |