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Convert C/C++ code to assembly language

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We use g++ compiler to turn provided C code into assembly language. To see the assembly code generated by the C compiler, we can use the “-S” option on the command line: 
 

Syntax:  

$ gcc -S filename.c


This will cause gcc to run the compiler, generating an assembly file. Suppose we write a C code and store it in a file name “geeks.c” .  

C

// C code stored in geeks.c file
#include <stdio.h>
 
// global string
char s[] = "GeeksforGeeks";
 
// Driver Code
int main()
{
    // Declaring variables
    int a = 2000, b =17;
     
    // Printing statement
    printf("%s %d \n", s, a+b);
}

                    

Running the command: 

$ gcc -S geeks.c


This will cause gcc to run the compiler, generating an assembly file geeks.s, and go no further. (Normally it would then invoke the assembler to generate an object- code file.)
The assembly-code file contains various declarations including the set of lines: 

CPP

    .section    __TEXT, __text, regular, pure_instructions
    .macosx_version_min 10, 12
    .global    _main
    .align    4, 0x90
_main:                                  ## @main
    .cfi_startproc
## BB#0:
    pushq    %rbp
Ltmp0:
    .cfi_def_cfa_offset 16
Ltmp1:
    .cfi_offset %rbp, -16
    movq    %rsp, %rbp
Ltmp2:
    .cfi_def_cfa_register %rbp
    subq    $16, %rsp
    leaq    L_.str(%rip), %rdi
    leaq    _s(%rip), %rsi
    movl    $2000, -4(%rbp)         ## imm = 0x7D0
    movl    $17, -8(%rbp)
    movl    -4(%rbp), %eax
    addl    -8(%rbp), %eax
    movl    %eax, %edx
    movb    $0, %al
    callq    _printf
    xorl    %edx, %edx
    movl    %eax, -12(%rbp)         ## 4-byte Spill
    movl    %edx, %eax
    addq    $16, %rsp
    popq    %rbp
    retq
    .cfi_endproc
 
    .section    __DATA, __data
    .global    _s                      ## @s
_s:
    .asciz    "GeeksforGeeks"
 
    .section    __TEXT, __cstring, cstring_literals
L_.str:                                 ## @.str
    .asciz    "%s %d \n"
 
 
.subsections_via_symbols

                    

Each indented line in the above code corresponds to a single machine instruction. For example, the pushq instruction indicates that the contents of register %rbp should be pushed onto the program stack. All information about local variable names or data types has been stripped away. We still see a reference to the global 
variable s[]= “GeeksforGeeks”, since the compiler has not yet determined where in memory this variable will be stored.



Last Updated : 30 Aug, 2021
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