x264中的汇编：cpu-a.asm——003

淡淡的烟草味﹌ 2022-06-10 08:30 156阅读 0赞

http://blog.csdn.net/xiaoyi247/article/details/7917537

CPUID指令是用来搜集当前程序正在运行的处理器信息的，包括厂商和信号信息。在IA-32中，CPUID指令使用EAX寄存器作为输入，EAX寄存器用来指定需要查看的信息的类型，根据EAX的数值的不同，CPUID指令会产生不同的信息，存入EBX,ECX,EDX寄存器中。

下面的表格显示了在指定不同的EAX的值的时候，得到的CPU的信息

<table> 
 <tbody> 
  <tr> 
   <td>EAX&nbsp;Value</td> 
   <td>CPUID Output</td> 
  </tr> 
  <tr> 
   <td>0</td> 
   <td>Vendor ID string, and the maximum CPUID option value&nbsp;supported</td> 
  </tr> 
  <tr> 
   <td>1</td> 
   <td>Processor type, family, model, and stepping information</td> 
  </tr> 
  <tr> 
   <td>2</td> 
   <td>Processor cache configuration</td> 
  </tr> 
  <tr> 
   <td>3</td> 
   <td>&nbsp;Processor serial number</td> 
  </tr> 
  <tr> 
   <td>4</td> 
   <td>Cache configuration (number of threads, number of cores, and<br> physical properties)</td> 
  </tr> 
  <tr> 
   <td>5</td> 
   <td>Monitor information</td> 
  </tr> 
  <tr> 
   <td>80000000h&nbsp;</td> 
   <td>Extended vendor ID string and supported levels</td> 
  </tr> 
  <tr> 
   <td>80000001h</td> 
   <td>&nbsp;Extended processor type, family, model, and stepping information</td> 
  </tr> 
  <tr> 
   <td>80000002h</td> 
   <td>&nbsp;Extended processor name string</td> 
  </tr> 
 </tbody> 
</table>

或者更详细的信息，可以参看INTEL的文档

Intel® Processor Identification and the CPUID Instruction

[http://www.intel.com/content/www/us/en/processors/processor-identification-cpuid-instruction-note.html?wapkw=cpuid][http_www.intel.com_content_www_us_en_processors_processor-identification-cpuid-instruction-note.html_wapkw_cpuid]

当EAX为0时，CPUID指令产生一个字符串，将存入EBX,EDX和ECX中。其中，EBX包含字符串的后面四个字符，EDX包含中间四个字符，ECX包含前面四个字符。

x264中的汇编代码解析

cglobal x264\_cpu\_cpuid, 5,7  
    push    rbx  
    mov     r11,   r1  
    mov     r10,   r2  
    movifnidn r9,  r3  
    movifnidn r8,  r4  
    mov     eax,   r0d;将要指定的参数存入到eax中  
    cpuid  
    mov     \[r11\], eax;将操作结果存入eax,ebx,ecx,edx  
    mov     \[r10\], ebx  
    mov     \[r9\],  ecx  
    mov     \[r8\],  edx  
    pop     rbx  
    RET

cpu.c中根据的到的数据来判断是否支持某种多媒体指令

x264\_cpu\_cpuid( 1, &eax, &ebx, &ecx, &edx );  
    if( edx&0x00800000 )  
        cpu |= X264\_CPU\_MMX;  
    else  
        return 0;  
    if( edx&0x02000000 )  
        cpu |= X264\_CPU\_MMXEXT|X264\_CPU\_SSE;  
    if( edx&0x04000000 )  
        cpu |= X264\_CPU\_SSE2;  
    if( ecx&0x00000001 )  
        cpu |= X264\_CPU\_SSE3;  
    if( ecx&0x00000200 )  
        cpu |= X264\_CPU\_SSSE3;  
    if( ecx&0x00080000 )  
        cpu |= X264\_CPU\_SSE4;  
    if( ecx&0x00100000 )  
        cpu |= X264\_CPU\_SSE42;

[http_www.intel.com_content_www_us_en_processors_processor-identification-cpuid-instruction-note.html_wapkw_cpuid]: http://www.intel.com/content/www/us/en/processors/processor-identification-cpuid-instruction-note.html?wapkw=cpuid