global directive, or you can define them in a linker command file using a linker assignment statement. set directive in combination with either the. You can define global constants in assembly language by using the. This creates an undeclared external reference that the linker resolves.ģ.6.3.2. global directive in the assembly language module. Likewise, to access a C/C++ function or object from assembly language, declare the C/C++ object with the. This declares the symbol as external and allows the linker to resolve references to it. global directive in the assembly language modifier. See Disable Name Demangling (–no_demangle) for details.Īny object or function declared in assembly language that is accessed or called from C/C++ must be declared with the. Thus, when you write assembly language code, you must use the same linknames as those assigned by the compiler. The compiler assigns linknames to all external objects. Disrupting the tables by putting other information in. cinit section consists entirely of initialization tables. The C/C++ startup routine assumes that the. cinit section for any purpose other than autoinitialization of global variables. Double values are returned in R0 and R1, and structures are returned as described in Step 2 of How a Function Makes a Call. If the contents of any of these registers must be preserved across the call, you must explicitly save them.įunctions must return values correctly according to their C/C++ declarations. Remember that a function can alter any register not designated as being preserved without having to restore it. When you call a C/C++ function from assembly language, load the designated registers with arguments and push the remaining arguments onto the stack as described in How a Function Makes a Call. For more information, see Interrupt Handling. Interrupt routines must save all the registers they use. In other words, the assembly function is free to use the stack as long as anything that is pushed onto the stack is popped back off before the function returns (thus preserving SP).Īny register that is not dedicated can be used freely without first being saved. If the SP is used normally, it does not need to be explicitly preserved. Save-on-entry registers (R4-R11 (alternate names are V1 to V8 and LR)).You must preserve any dedicated registers modified by a function. C/C++ code can access variables and call functions defined in assembly language, and assembly code can access C/C++ variables and call C/C++ functions.įollow these guidelines to interface assembly language and C:

Interfacing C/C++ with assembly language functions is straightforward if you follow the calling conventions defined in Function Structure and Calling Conventions, and the register conventions defined in Register Conventions.

Using Assembly Language Modules With C/C++ Code ¶

Call c function from asm iar arm