down() function and assembly implementation

[Deepak Joshi <deepak_cins@xxxxxxxxxxx>]

Hi all,
 
 I am not getting the implementation of down() which is written in assembly language. 
 
 static inline void down(struct semaphore * sem)
 {
 #if WAITQUEUE_DEBUG
         CHECK_MAGIC(sem->__magic);
 #endif
                                                                                                                              
         __asm__ __volatile__(
                 "# atomic down operation\n\t"
                 LOCK "decl %0\n\t"     /* --sem->count */
                 "js 2f\n"
                 "1:\n"
                 LOCK_SECTION_START("")
                 "2:\tcall __down_failed\n\t"
                 "jmp 1b\n"
                 LOCK_SECTION_END
                 :"=m" (sem->count)
                 :"c" (sem)
                 :"memory");
 }
 
 if u look into the assembly produced by compiling it using -S option for gcc you will get 
 
 
 #APP
         # atomic down operation
         lock ; decl (%eax)
         js 2f
 1:
 .subsection 1
         .ifndef .text.lock.KBUILD_BASENAME
         .text.lock.KBUILD_BASENAME:
         .endif
         2:      call __down_failed
         jmp 1b
 .previous
                                                                                                                              
 #NO_APP
 
 In the above listing its jumping forward first and calls __down_failed and after that again it jumps backword to label one. Why is it so ??? and also whats the meaning of       
          .ifndef .text.lock.KBUILD_BASENAME
          .text.lock.KBUILD_BASENAME:
          .endif
 above assembly code. Plz guide me.
 
 Thanks in advance,
 Deepak Joshi.

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