gcc asm '.section.text.lock"

miaowei · **Joined:** Wed Dec 18, 2013 9:10 am **Posts:** 84

I am reading the source code of linux 2.4.
The following code is the entry of 'up' operation of semaphore. It's located in include/asm-i386-semaphore.h .

Code:

static inline void down(struct semaphore * sem)
{
   __asm__ __volatile__(
      "# atomic down operation\n\t"
      LOCK "decl %0\n\t"     /* --sem->count */
      "js 2f\n"
      "1:\n"
      ".section .text.lock,\"ax\"\n"       /* I don't understand this line*/
      "2:\tcall __down_failed\n\t"
      "jmp 1b\n"
      ".previous"
      :"=m" (sem->count)
      :"c" (sem)
      :"memory");
}

This line :
".section .text.lock,\"ax\"\n"
What's he doing? The syntax seems horrible. I even don't know how to google it.

Could any friend help me? Thanks!

miaowei · **Joined:** Wed Dec 18, 2013 9:10 am **Posts:** 84

I see. The code between

Code:

".section .text.lock, \"ax"\n"
...
".previous"

is sent to a special section by gcc.
Because these instructions are not often 'hit', we separate them to another place to get a shorter function body of down().

But i still don't understand what 's the meaning of 'ax'.

Octocontrabass · **Joined:** Mon Mar 25, 2013 7:01 pm **Posts:** 5137

miaowei wrote:

But i still don't understand what 's the meaning of 'ax'.

It's explained in the manual.

miaowei · **Joined:** Wed Dec 18, 2013 9:10 am **Posts:** 84

Octocontrabass wrote:

miaowei wrote:

But i still don't understand what 's the meaning of 'ax'.

It's explained in the manual.

Thank you very much, Octocontrabass.
I treated it as the 'AX' register ...

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gcc asm '.section.text.lock"

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