GCC中嵌入式汇编的一般形式

asm volatile ("asm routine" : output : input : modify);

 

#define switch_to(prev,next,last) do {                    
    asm volatile("pushl %%esi "                    
             "pushl %%edi "                    
             "pushl %%ebp "                    
             "movl %%esp,%0 "    /* save ESP */        
             "movl %3,%%esp "    /* restore ESP */    
             "movl $1f,%1 "        /* save EIP */        
             "pushl %4 "        /* restore EIP */    
             "jmp __switch_to "                
             "1: "                        
             "popl %%ebp "                    
             "popl %%edi "                    
             "popl %%esi "                    
             :"=m" (prev->thread.esp),"=m" (prev->thread.eip),    
              "=b" (last)                    
             :"m" (next->thread.esp),"m" (next->thread.eip),    
              "a" (prev), "d" (next),                
              "b" (prev));                    
} while (0)

上面的代码汇编之后大致如下：

#define switch_to(prev,next,last) do {            
    asm volatile("pushl %%esi "                
             "pushl %%edi "                    
             "pushl %%ebp "                    
             "movl %%esp,(prev->thread.esp) "/* save ESP */        
             "movl (next->thread.esp),%%esp "/* restore ESP */    
             "movl $1f,(prev->thread.eip) "    /* save EIP */        
             "pushl (next->thread.eip) "        /* restore EIP */    
             "jmp __switch_to "                
             "1: "                                
             "popl %%ebp "                    
             "popl %%edi "                    
             "popl %%esi "                    
             :"=m" (prev->thread.esp),"=m" (prev->thread.eip),    
              "=b" (last)                    
             :"m" (next->thread.esp),"m" (next->thread.eip),    
              "a" (prev), "d" (next),                
              "b" (prev));                    
} while (0)

m = memory

b = ebx

a = eax

d = edx

 f = forward