Assembly and C Language

# File: Hello. C # include <stdio. h> # include <string. h> extern void printk (char); extern int max_p (INT, INT); char STR [] = "Hello world! \ N "; int main () {int I; for (I = 0; I <strlen (STR); I ++) printk (STR [I]); int max = max_p (18,200); printf ("% d \ n", max); printf ("% d \ n", max_p (10, 2 ));} # file: printk. s # include <stdio. h>. text. global printk. type printk, % function. global max_p.type max_p, % function. alignprintk :. fnstart extends FDSP !, {R0, r4-r7, LR}/* Register pressure stack */mov R1, r0mov r0, r1bl putcharreturn: ldmfdsp !, {R0, r4-r7, PC}/* LR save Pc value, input parameter: R0 ~ R3, return: R0 */. fnendmax_p:/*. fnstart */define fd sp !, {R4-r7, LR} CMP r0, r1bcs 1f/* cs as condition judgment, greater than or equal to 0 */mov r0, R11: ldmfd SP !, {R4-r7, PC}/*. fnend */# file: Build. Sh #! /Bin/Sharm-None-Linux-gnueabi-as printk. s-O printk. oarm-None-Linux-gnueabi-gcc-C hello. carm-None-Linux-gnueabi-gcc-static hello. O printk. o-O hello

# Include <stdio. h> memset:/* compute the offset to align the destination * offset = (4-(SRC & 3) & 3 =-Src & 3 */. fnstart. save {r0, r4-r7, LR} 127fd SP !, {R0, r4-r7, LR} RSB R3, R0, #0 ands R3, R3, #3 CMP R3, R2 movhi R3, R2/* splat R1 */mov R1, R1, LSL #24 Orr R1, R1, R1, LSR #8 Orr R1, R1, R1, LSR #16/* memset (void *, Int, INT) the second parameter only takes 8 lower bits of data, and the other bits use this bit to fill in the rush * // * if not aligned, the data is copied as this, for example, R3 = 3, r3 <post 31 CS flag is valid, and the maximum bit 1 OF R12 is valid */movs R12, R3, LSL #31 strcsb R1, [R0], #1/* can't use strh (alignment unknown) */strcsb R1, [R0], #1 strmib R1, [R0], #1 subs R2, R2, R3/* 1 ~ When three data entries exist, the function returns */ldmlsfd SP !, {R0, r4-r7, LR}/* ls flags indicate less than or equal to 0, return */bxls LR/* align the destination to a cache-line */mov R12, r1 mov LR, R1 mov R4, R1 mov R5, R1 mov R6, R1 mov R7, R1/* and R1 and R3 */RSB R3, R0, #0 ands R3, r3, # 0x1c beq aligned32/* 32 bytes aligned */CMP R3, r2/* calculate the number of bytes to be aligned with 32 bytes */andhi R3, R2, # 0x1c sub R2, R2, r3/* conditionnaly writes 0 to 7 words (length in R3) * // * a maximum of 28 Bytes: 16 + 8 + 4 */ Movs R3, R3, LSL #28 stmcsia R0 !, {R1, LR} stmcsia R0 !, {R1, LR} already miia R0 !, {R1, LR} movs R3, R3, LSL #2 strcs R1, [R0], #4 aligned32: subs R2, R2, #32/* count-= 32 */mov R3, R1 BMI 2f 1: subs R2, R2, #32 stmia R0 !, {R1, R3, R4, R5, R6, R7, R12, LR}/* store 32 bytes at a time */BHS 1B/* If the value is greater than or equal to 0, the cycle is as follows: do {r2 = R2-32; copy;} while (r2> = 0); */2: Add R2, R2, #32/* The Last 0 ~ 31 bytes */