kernel hexdump分析

驅動調試中,很多時候是二進制的，這個時候hexdump就是個非常有用的工具了。
不要再自己去實現類似的功能，kernel代碼裡面就有：
參考： kernel/lib/hexdump.c
// 0Xxx轉換成 ASCII ,實現簡單巧妙

const char hex_asc[] = "0123456789abcdef";
#define hex_asc_lo(x)	hex_asc[((x) & 0x0f)]
#define hex_asc_hi(x)	hex_asc[((x) & 0xf0) >> 4]

void hex_dump_to_buffer(const void *buf, size_t len, int rowsize,
			int groupsize, char *linebuf, size_t linebuflen,
			bool ascii)
{
	const u8 *ptr = buf;
	u8 ch;
	int j, lx = 0;
	int ascii_column;
        // 每行固定16或者32個字節，符合國際審美觀
	if (rowsize != 16 && rowsize != 32)
		rowsize = 16;

	if (!len)
		goto nil;
	if (len > rowsize)		/* limit to one line at a time */
		len = rowsize;
	if ((len % groupsize) != 0)	/* no mixed size output */
		groupsize = 1;

	switch (groupsize) {
	......
	default:
                //  轉換成ASCii 形式
		for (j = 0; (j < len) && (lx + 3) <= linebuflen; j++) {
			ch = ptr[j];
			linebuf[lx++] = hex_asc_hi(ch);
			linebuf[lx++] = hex_asc_lo(ch);
			linebuf[lx++] = ' ';
		}
		if (j)
			lx--;

		ascii_column = 3 * rowsize + 2;
		break;
	}
	if (!ascii)
		goto nil;
        // 加上對應的ASCII字符串，區別如下：
        //  0009ab42: 40 41 42 43 44 45 46 47 48 49 4a 4b 4c 4d 4e 4f  @ABCDEFGHIJKLMNO
        //  0009ab42: 40 41 42 43 44 45 46 47 48 49 4a 4b 4c 4d 4e 4f  
	while (lx < (linebuflen - 1) && lx < (ascii_column - 1))
		linebuf[lx++] = ' ';
	for (j = 0; (j < len) && (lx + 2) < linebuflen; j++) {
		ch = ptr[j];
		linebuf[lx++] = (isascii(ch) && isprint(ch)) ? ch : '.';
	}
nil:
        // 記得加上結束符號，有可能導致printk --> kernel panic 
	linebuf[lx++] = '\0';
}

void print_hex_dump(const char *level, const char *prefix_str, int prefix_type,
		    int rowsize, int groupsize,
		    const void *buf, size_t len, bool ascii)
{
	const u8 *ptr = buf;
	int i, linelen, remaining = len;
        /* 每行數據類似下面
           40 41 42 43 44 45 46 47 48 49 4a 4b 4c 4d 4e 4f  @ABCDEFGHIJKLMNO
           |                                          |  |                 |
           -----------------------------------------------
                    16*3 or 32*3                       2      32+1 
        */
	unsigned char linebuf[32 * 3 + 2 + 32 + 1];

	if (rowsize != 16 && rowsize != 32)
		rowsize = 16;

	for (i = 0; i < len; i += rowsize) {
		linelen = min(remaining, rowsize);
		remaining -= rowsize;
                //  linebuf 返回需要打印的字符串
		hex_dump_to_buffer(ptr + i, linelen, rowsize, groupsize,
				   linebuf, sizeof(linebuf), ascii);
                 
                // 是否使用前綴
		switch (prefix_type) {
                     // 加上絕對地址
		case DUMP_PREFIX_ADDRESS:
			printk("%s%s%p: %s\n",
			       level, prefix_str, ptr + i, linebuf);
			break;
                     // 只是簡單地加上偏移量而已
		case DUMP_PREFIX_OFFSET:
			printk("%s%s%.8x: %s\n", level, prefix_str, i, linebuf);
			break;
		default:
			printk("%s%s%s\n", level, prefix_str, linebuf);
			break;
		}
	}
}

// 一般在kernel代碼中，調用此接口，許多參數用默認的，不需要了解太多細節
void print_hex_dump_bytes(const char *prefix_str, int prefix_type,
			  const void *buf, size_t len)
{
	print_hex_dump(KERN_DEBUG, prefix_str, prefix_type, 16, 1,
		       buf, len, true);
}