編譯linux 0.0.1 =>錯誤：'asm'操作數具有不可能的約束__asm __（“ cld \\ n”

Question

我正在嘗試從我的64位Intel計算機上的源代碼編譯linux內核0.0.1。 只是為了填寫引導程序和主程序，我不得不修改所有makefile以獲得32位編譯。

因此，這是make的輸出：

In file included from traps.c:7:0:
../include/string.h:128:22: warning: conflicting types for built-in function ‘strchr’
 extern inline char * strchr(const char * s,char c)
                      ^
../include/string.h:145:22: warning: conflicting types for built-in function ‘strrchr’
 extern inline char * strrchr(const char * s,char c)
                      ^
../include/string.h:379:22: warning: conflicting types for built-in function ‘memchr’
 extern inline void * memchr(const void * cs,char c,int count)
                      ^
../include/string.h:395:22: warning: conflicting types for built-in function ‘memset’
 extern inline void * memset(void * s,char c,int count)
                      ^
In file included from traps.c:11:0:
../include/linux/kernel.h:5:1: warning: function return types not compatible due to ‘volatile’
 volatile void panic(const char * str);
 ^
../include/linux/kernel.h:5:1: warning: function return types not compatible due to ‘volatile’
../include/linux/kernel.h:5:1: warning: function return types not compatible due to ‘volatile’
In file included from traps.c:7:0:
../include/string.h: In function ‘strcpy’:
../include/string.h:29:1: error: ‘asm’ operand has impossible constraints
 __asm__("cld\n"
 ^
Makefile:24: set di istruzioni per l'obiettivo "traps.o" non riuscito

string.h的代碼部分如下：

extern inline char * strcpy(char * dest,const char *src)
{
__asm__("cld\n"
    "1:\tlodsb\n\t"
    "stosb\n\t"
    "testb %%al,%%al\n\t"
    "jne 1b"
    ::"S" (src),"D" (dest):"si","di","ax");
return dest;
}

我不知道為什么原始代碼無法編譯。 到目前為止，我已成功編譯：boot和init子目錄。

非常感謝

Answer 1

我認為問題在於寄存器緩沖區列表與輸入重疊。

也就是說， "S"代表寄存器esi而"D"代表寄存器edi ； 但隨后的清單列表包含"si"和"di" ，它們是這些寄存器的低16位。 也許舊的GCC版本忽略了這一點，但是新版本不允許重疊。

從這里的文檔 ：

垃圾描述可能不會與輸入或輸出操作數重疊。

解決方案，只需將它們從列表中刪除：

...
::"S" (src),"D" (dest) :"ax", "cc");

順便說一句，我也將“ Cb "cc"添加到了"cc"因為該程序集修改了e標志。