uclinux-2008R1-RC8(bf561)到VDSP5的移植(48):__cmpxchg的問題

在include/asm/system.h下有一個__cmpxchg函數：

/*
 * Atomic compare and exchange. Compare OLD with MEM, if identical,
 * store NEW in MEM. Return the initial value in MEM. Success is
 * indicated by comparing RETURN with OLD.
 */
static inline unsigned long __cmpxchg(volatile void *ptr, unsigned long old,
                         unsigned long new, int size)
{
     unsigned long tmp = 0;
     unsigned long flags = 0;
     local_irq_save(flags);
     switch (size) {
     case 1:
         __asm__ __volatile__
              ("%0 = b%3 (z);/n/t"
               "CC = %1 == %0;/n/t"
               "IF !CC JUMP 1f;/n/t"
               "b%3 = %2;/n/t"
               "1:/n/t"
               : "=&d" (tmp) : "d" (old), "d" (new), "m" (*__xg(ptr)) : "memory");
         break;
     case 2:
         __asm__ __volatile__
              ("%0 = w%3 (z);/n/t"
               "CC = %1 == %0;/n/t"
               "IF !CC JUMP 1f;/n/t"
               "w%3 = %2;/n/t"
               "1:/n/t"
               : "=&d" (tmp) : "d" (old), "d" (new), "m" (*__xg(ptr)) : "memory");
         break;
     case 4:
         __asm__ __volatile__
              ("%0 = %3;/n/t"
               "CC = %1 == %0;/n/t"
               "IF !CC JUMP 1f;/n/t"
               "%3 = %2;/n/t"
               "1:/n/t"
               : "=&d" (tmp) : "d" (old), "d" (new), "m" (*__xg(ptr)) : "memory");
         break;
     }
     local_irq_restore(flags);
     return tmp;
}

在VDSP下編譯將產生如下語法錯誤：

"../../include/asm/system.h", line 209: cc1101: error: invalid constraint in
          asm statement
   : "=&d" (tmp) : "d" (old), "d" (new), "m" (*__xg(ptr)) : "memory");
                                         ^
"../../include/asm/system.h", line 209: cc1155: error: gnu asm operand
          requires integral or pointer type
   : "=&d" (tmp) : "d" (old), "d" (new), "m" (*__xg(ptr)) : "memory");
                                              ^
"../../include/asm/system.h", line 218: cc1101: error: invalid constraint in
          asm statement
   : "=&d" (tmp) : "d" (old), "d" (new), "m" (*__xg(ptr)) : "memory");
                                         ^
"../../include/asm/system.h", line 218: cc1155: error: gnu asm operand
          requires integral or pointer type
   : "=&d" (tmp) : "d" (old), "d" (new), "m" (*__xg(ptr)) : "memory");
                                              ^
"../../include/asm/system.h", line 227: cc1101: error: invalid constraint in
          asm statement
   : "=&d" (tmp) : "d" (old), "d" (new), "m" (*__xg(ptr)) : "memory");
                                         ^
"../../include/asm/system.h", line 227: cc1155: error: gnu asm operand
          requires integral or pointer type
   : "=&d" (tmp) : "d" (old), "d" (new), "m" (*__xg(ptr)) : "memory");
                                              ^
6 errors detected in the compilation of "../../fs/sysfs/dir.c".
cc3089: fatal error: Compilation failed

首先，VDSP的嵌入匯編不支持”m”這個constraint，但是可以用”a”來替換。

其次，VDSP的嵌入匯編不支持"a" (*__xg(ptr))結構體的傳遞，可以直接使用"a" (ptr)，所得到的結果和GCC的相一致。

在改正完上面兩個錯誤後，還有更奇怪的問題：

[Error ea5003] "c:/temp/acc01786adb000/acc01786adb001.s":138 Semantic Error in instruction :
IF !CC JUMP 1f;
Operands don't fit instruction template 'IF BANG CC JUMP expr'.
Check for an out of range immediate value or an illegal register.
[Error ea5004] "c:/temp/acc01786adb000/acc01786adb001.s":138 Syntax Error in :
IF !CC JUMP 1f;
syntax error is at or near text 'f'.
Attempting error recovery by ignoring text until the ';'
[Error ea5004] "c:/temp/acc01786adb000/acc01786adb001.s":139 Syntax Error in :
wP1 = R1;
syntax error is at or near text '='.
Attempting error recovery by ignoring text until the ';'
[Error ea5007] "c:/temp/acc01786adb000/acc01786adb001.s":140 The label "1:" is illegal because it begins with a digit. If this is GNU assembly source, rewrite to a local temporary name of your choosing. If the GNU assembly code was generated from a macro, the VisualDSP++ preprocessing label auto-generation feature ("?") can be used to generate a unique local label.
[Error ea5003] "c:/temp/acc01786adb000/acc01786adb001.s":158 Semantic Error in instruction :
IF !CC JUMP 1f;
Operands don't fit instruction template 'IF BANG CC JUMP expr'.
Check for an out of range immediate value or an illegal register.
[Error ea5004] "c:/temp/acc01786adb000/acc01786adb001.s":158 Syntax Error in :
IF !CC JUMP 1f;
syntax error is at or near text 'f'.
Attempting error recovery by ignoring text until the ';'
[Error ea5007] "c:/temp/acc01786adb000/acc01786adb001.s":160 The label "1:" is illegal because it begins with a digit. If this is GNU assembly source, rewrite to a local temporary name of your choosing. If the GNU assembly code was generated from a macro, the VisualDSP++ preprocessing label auto-generation feature ("?") can be used to generate a unique local label.
Previous errors prevent assembly
Assembler totals: 7 error(s) and 0 warning(s)
cc3089: fatal error: Assembler failed

如果不是剛改完此函數，幾乎無法知道錯誤的來源在哪裡!

根據提示檢查上述匯編代碼，修改jump 1f之類的跳轉後OK。

而對於wP1 = R1;這樣的錯誤則改為w[%3]之類的。

修改完後的函數如下：

/*
 * Atomic compare and exchange. Compare OLD with MEM, if identical,
 * store NEW in MEM. Return the initial value in MEM. Success is
 * indicated by comparing RETURN with OLD.
 */
static inline unsigned long __cmpxchg(volatile void *ptr, unsigned long old,
                         unsigned long new, int size)
{
     unsigned long tmp = 0;
     unsigned long flags = 0;
     local_irq_save(flags);
     switch (size) {
     case 1:
         __asm__ __volatile__
              ("%0 = b[%3] (z);/n/t"
               "CC = %1 == %0;/n/t"
               "IF !CC JUMP __cmpxchg_size_1;/n/t"
               "b[%3] = %2;/n/t"
               "__cmpxchg_size_1:/n/t"
               : "=&d" (tmp) : "d" (old), "d" (new), "a" (ptr) : "memory");
         break;
     case 2:
         __asm__ __volatile__
              ("%0 = w[%3] (z);/n/t"
               "CC = %1 == %0;/n/t"
               "IF !CC JUMP __cmpxchg_size_2;/n/t"
               "w[%3] = %2;/n/t"
               "__cmpxchg_size_2:/n/t"
               : "=&d" (tmp) : "d" (old), "d" (new), "a" (ptr) : "memory");
         break;
     case 4:
         __asm__ __volatile__
              ("%0 = %3;/n/t"
               "CC = %1 == %0;/n/t"
               "IF !CC JUMP __cmpxchg_size_4;/n/t"
               "%3 = %2;/n/t"
               "__cmpxchg_size_4:/n/t"
               : "=&d" (tmp) : "d" (old), "d" (new), "a" (ptr) : "memory");
         break;
     }
     local_irq_restore(flags);
     return tmp;
}