Linux Macros: __assembly__

Compilation: assembly

Guess: So this macro is related to the assembly?!

Reference: Some of the constant macros are referenced by both C and ASM, while C and ASM differ in the processing of the immediate number symbol . In ASM, directives are adopted to differentiate whether the operands are signed or unsigned, rather than through the operands. and C is through the property of the variable, not through the operator. c If you want to indicate that a constant is unsigned, you must add a suffix to the constant, and ASM is indicated by using a different directive. Thus, when a constant is contained by both C and ASM, different processing must be done. So Kbuild_aflags will add an d__assembly__ to tell the preprocessor that this is ASM.

/*linux-3.08/include/linux/const.h*//*Const.h:macros for dealing with constants. */#ifndef _linux_const_h#define_linux_const_h/*Some constant macros is used in both assembler and * C code.  Therefore We cannot annotate them always with * ' UL ' and other type specifiers unilaterally. We * Use the following macros to deal with this. * * Similarly, _at () would cast an expression with a type in C, but * leave it unchanged in ASM. */
/*
* The note above says: Some of the constant macros are used in both assembly and C, however, we cannot add a "UL" or other suffix as the macro constants of note C. So we need to use the following macro to solve this problem.
* For example call: #define DEMO_MACRO _at (1, UL): In C will be interpreted as #define DEMO_MACRO 1UL, and in the Assembly do nothing, that is: #define DEMO_MACRO 1
*/
#ifdef __assembly__#define_ac (x, y) X#define_at (t,x) X#else#define__ac (x, y) (x# #Y)#define_ac (x, y) __ac (x, y)#define_at (T,x) ((T) (X))#endif#endif/* ! (_linux_const_h) */

Linux Macros: __assembly__