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memset_explicit.c
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memset_explicit.c
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/*
* ---------------------------------------------------------------------------
* Filename: memset_explicit.c
* Description: A custom `memset()` implementation to force bypass GCC/Clang
* optimization
*
* Version: 1.0
* Created: 03/19/2015 01:41:49
* Revision: none
* Compiler: gcc, clang, armcc
*
* Author: Babil Golam Sarwar (gsbabil)
* Email: [email protected]
* ---------------------------------------------------------------------------
*/
#include <stdlib.h>
#include <string.h>
#include <stdio.h>
#include "memset_explicit.h"
#define memset_explicit_x86(buf, val, len) \
__asm__ __volatile__("\n\trep stos %1, (%0)" \
: \
: "D"((buf)), "a"((unsigned char)(val)), \
"c"((len) / sizeof(unsigned char)) \
: "memory")
/*
* #if defined(__EMBEDDED__)
* #define memset_explicit_arm(buf, val) \
* __asm__ __volatile__("mov r4, %[val] \n\tstmia %[buf]!, {r4} \n\t"
* :
* : [val] "r"(val), [buf] "r"(buf)
* : "r4", "memory")
* #endif
*/
#if __ARM_ARCH == 7 || defined(__EMBEDDED__)
#define memset_explicit_arm(buf, val) \
__asm__ __volatile__("mov r4, %[val]\n\tmov r5, %[buf]\n\tstr r4, [r5]" \
: \
: [val] "r"((unsigned int)val), [buf] "r"(buf) \
: "r4", "r5", "memory")
#endif
#if __ARM_ARCH == 8
#define memset_explicit_arm(buf, val) \
__asm__ __volatile__("mov x4, %[val]\n\tmov x5, %[buf]\n\tstr x4, [x5]" \
: \
: [val] "r"((unsigned long)val), [buf] "r"(buf) \
: "x4", "x5", "memory")
#endif
void __attribute__((noinline))
memset_explicit(unsigned char* buf, unsigned char val, size_t buf_len) {
#if defined(__ARM_ARCH)
int i = 0;
for (i = 0; i < buf_len; i++) {
buf[i] = val;
memset_explicit_arm(buf, val);
/*
* asm volatile("mov x4, %[val]"
* :
* : [val] "r"((unsigned long)val)
* : "x4", "memory");
* asm volatile("mov x5, %[buf]"
* :
* : [buf] "r"((unsigned long)buf)
* : "x5", "memory");
* asm volatile("str x4, [x5]" : : : "x4", "x5",
* "memory");
*/
buf = buf + 1;
}
#else
memset_explicit_x86(buf, val, buf_len);
#endif
}
int main() {
char buffer[4];
buffer[0] = 'A';
buffer[1] = 'B';
buffer[2] = 'C';
buffer[3] = 'D';
/*
* memset((unsigned char*)buffer, 0x00, sizeof(buffer));
*/
memset_explicit((unsigned char*)buffer, 0x00, sizeof(buffer));
return 0;
}