6.6.5 Using Inline Assembly Language

Within a C/C++ program, you can use the asm statement to insert a single line of assembly language into the assembly language file created by the compiler. A series of asm statements places sequential lines of assembly language into the compiler output with no intervening code. For more information, see Section 5.11.

The asm statement is useful for inserting comments in the compiler output. Simply start the assembly code string with a semicolon (;) as shown below:

asm(";*** this is an assembly language comment");

NOTE

Using the asm Statement

Keep the following in mind when using the asm statement:

Be extremely careful not to disrupt the C/C++ environment. The compiler does not check or analyze the inserted instructions.
Avoid inserting jumps or labels into C/C++ code because they can produce unpredictable results by confusing the register-tracking algorithms that the code generator uses.
Do not change the value of a C/C++ variable when using an asm statement. This is because the compiler does not verify such statements. They are inserted as is into the assembly code, and potentially can cause problems if you are not sure of their effect.
Do not use the asm statement to insert assembler directives that change the assembly environment.
Avoid creating assembly macros in C code and compiling with the --symdebug:dwarf (or -g) option. The C environment’s debug information and the assembly macro expansion are not compatible.