gnu cc扩展和ABI

gnc cc扩展标准c的语法，非常强大！！！详情请见：

http://uw714doc.sco.com/cgi-bin/info2html?%28gcc.info%29C%2520Extensions&lang=en

http://tigcc.ticalc.org/doc/gnuexts.html#SEC104

https://gcc.gnu.org/onlinedocs/gcc-4.4.5/gcc/C-Extensions.html#C-Extensions

ABI是application binary interface的缩写，规定了struct布局，函数调用规则，数据大小等。

非常值得研究。

比如：x86-64下，rbx，rbp，r12-r15是called saved registers。

参考文献：http://www.x86-64.org/documentation/abi.pdf

people.freebsd.org/~obrien/amd64-elf-abi.pdf

 #define my_min(x, y)  ({const typeof(x) __x = x; \
     const typeof(y) __y = y; \
     (void) (&__x == &__y); \
     __x < __y ? __x : __y;})

 struct Str
 {
     int a;
     char b;
     short c;
 } __attribute__((packed));

 #define ERR_PRINTF(fmt, args...) {\
     ]; \
     snprintf(msg, sizeof(msg), "%s:%d "fmt"\n", __FUNCTION__, __LINE__, ##args);\
     printf("%s", msg); \
 }

 #define ERR_PRINTF2(fmt, ...) \
     printf("%s:%d "fmt"\n", __FUNCTION__, __LINE__, ##__VA_ARGS__)

 #define likely(x)  __builtin_expect((x), 1)
 #define unlikely(x)  __builtin_expect((x), 0)

 __attribute__ ((noinline))   bool CAS_64b(uint64_t* ptr, uint32_t* oldv, uint32_t* newv)
 {
     bool ret = false;
     __asm__ __volatile__ (
         "pushl %%ebx;"
         "movl %4, %%ebx;"
         "lock cmpxchg8b %1;\n"
         "sete %0;\n"
         "popl %%ebx;\n"
         :"=m"(ret),"+m"(*(uint64_t volatile*)(ptr))
         :]), ]), ]), ])
         :"memory");
         return ret;
 }

 //#if defined(__x86_64__)
 //#define CAS(ptr, oldv, newv)  __sync_bool_compare_and_swap((uint64_t*)(ptr), *(uint64_t*)(&oldv), *(uint64_t*)(&newv))
 //#else
 #define CAS(ptr, oldv, newv) CAS_64b((uint64_t*)(ptr), (uint32_t*)(&oldv), (uint32_t*)(&newv))
 //#endif
 struct A
 {
     int a;
     int b;
 };

 void test_CAS()
 {
     , };
     , };
     struct A sc = sa;
     if(CAS(&sc, sa, sb))
         printf("success, %d %d\n", sb.a, sb.b) ;
     else
         printf("fail, %d %d\n", sb.a, sb.b);
 }

 void f_unlikely()
 {
     printf("go unlikely\n");
 }

 void f_likely()
 {
     printf("go likely\n");
 }

 void test_aligned(char* p)
 {
     )>>)<<);
     *(()) = ;
 }

 void test_likely(int x)
 {
     if(unlikely(x))
         f_unlikely();
     else
         f_likely();
 }

 void test_return_addr()
 {
     );
     printf("address \t %p\n", p);
 }

 void test_frame_addr()
 {
     );
     printf("address \t %p\n", p);
 }

 int main()
 {
     //typeof
     //statement expression
     , );
     printf("%d\n", c);

     //packed
     printf("sizeof(Str) = %u\n", (uint32_t)sizeof(Str));

     //##
     ERR_PRINTF();
     ERR_PRINTF("test2");

     ERR_PRINTF2();
     //printf("%s:%d ""test2""\n", __FUNCTION__, 80, ); // the , still exists
     ERR_PRINTF2("test2");

     //__builtin_expect
     test_likely();

     //__builtin_return_address
     test_return_addr();

     //__builtin_frame_address
     test_frame_addr();

     //test aligned
     ] = {};
     test_aligned(pp);

     //test CAS
     test_CAS();

     )
         sleep();
     ;
 }

执行结果：

[ ~/code/test_sighup]$ ./test_gcc_ex
1
sizeof(Str) = 7
main:120 1 test
main:121 test2
main:123 1 test
main:125 test2
go unlikely
address          0x804882b
address          0xffb33aa8
success, 3 4

objdump -DC ./test_gcc_ex

00000000004006a0 <test_likely(int)>:
  4006a0:       85 ff                   test   %edi,%edi
  4006a2:       75 05                   jne    4006a9 <test_likely(int)+0x9>
  4006a4:       e9 d7 ff ff ff          jmpq   400680 <f_likely()>
  4006a9:       e9 e2 ff ff ff          jmpq   400690 <f_unlikely()>
  4006ae:       66 90                   xchg   %ax,%ax

参考代码：

http://blog.csdn.net/cugxueyu/article/details/1955372