GNU pseudo instruction definition function

Define a function in the assembly ,type,func Fine , Generally, you can use global Set global properties , For external use c Code to call

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The first one is , Using pseudo instructions  

.func   xx

MRS X0, SCTLR

RET

endfunc

atf Example

among func ,endfunc Is a macro

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The second kind , Use type

type Used to set the type of symbol , set the type of a symbol.

The official introduction ： 

Format ：

.type fun_name, @function  //@function It can be %function

fun_name:

    #content

ret
.type Instruction assignment fun_name Address when calling this function for other assemblers .
fun_name Also function name .
@function Indicates that the function content starts .
ret The instruction indicates the end of the function , Return to the place where the parent function calls the child function .

global Usage method ,

.global symbol, .globl symbol
.global makes the symbol visible to ld. If you define symbol in your partial program,
its value is made available to other partial programs that are linked with it. Otherwise,
symbol takes its attributes from a symbol of the same name from another file linked into
the same program.
Both spellings (‘.globl’ and ‘.global’) are accepted, for compatibility with other assemblers.

.global <symbol> This directive gives the symbol external linkage (similar to EXPORT in armasm).

Example

.global func1

.type func1   %function

func1:

MRS X0,ICC_XX

ret

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The third kind of , Use macro Macro definition defines functions and parameters

.macro   <name>   {<arg_1} //name must , The following parameters are optional
{,<arg_2>} ... {,<arg_N>} Just look at this example

.macro SHIFTLEFT a, b
.if \b < 0
MOV \a, \a, ASR #-\b
.exitm
.endif
MOV \a, \a, LSL #\b
.endm

Macros can be nested , Another macro can be called in the macro

atf Example