On Wed, Jul 7, 2010 at 8:55 AM, Preeti Sharma <pritis@xxxxxxxxx> wrote:
> Good to know that this is supposed to work (I am using 4.1.2) I get a
> link error in doing so
> here is my code:
>
> cat test1.c
> #include <stdio.h>
> #include <unistd.h>
> #include <errno.h>
>
> long long global_int = 0;
>
> int main()
> {
> __sync_fetch_and_add( &global_int, 1 );
> printf("Global int is : %d\n", global_int);
> }
> The link error I get is :
>
> gcc -D_GNU_SOURCE -D_REENTRANT -O2 -m32 -march=i686 -o test test1.c
> /tmp/cc4pniWE.o: In function `main':
> test1.c:(.text+0x29): undefined reference to `__sync_fetch_and_add_8'
> collect2: ld returned 1 exit status
>
>
>
>
> On Wed, Jul 7, 2010 at 8:43 AM, Andrew Haley <aph@xxxxxxxxxx> wrote:
>> On 07/07/2010 04:26 PM, Preeti Sharma wrote:
>>> I am trying to use __sync_fetch_and_add with type as "long long" .
>>>
>>> This gives me the link error :
>>> undefined reference to `__sync_fetch_and_add_8'
>>>
>>> This compiles for a "int " type though. I am using the the gcc option
>>> -march=i686
>>>
>>> Is it possible to do a 64 bit integer operation atomically with the
>>> __sync .. builtin functions ?
>>
>> Works for me:
>>
>> long long a;
>>
>> t()
>> {
>> __sync_fetch_and_add(&a, 1);
>> }
>>
>> $ gcc -S t.c -m32 -march=i686 -O2
>>
>> .file "t.c"
>> .text
>> .p2align 4,,15
>> .globl t
>> .type t, @function
>> t:
>> pushl %ebp
>> movl %esp, %ebp
>> subl $12, %esp
>> movl %ebx, (%esp)
>> movl %esi, 4(%esp)
>> movl %edi, 8(%esp)
>> movl a, %eax
>> movl a+4, %edx
>> .L2:
>> movl %eax, %esi
>> movl %edx, %edi
>> addl $1, %esi
>> adcl $0, %edi
>> movl %esi, %ebx
>> movl %edi, %ecx
>> lock cmpxchg8b a
>> jne .L2
>> movl (%esp), %ebx
>> movl 4(%esp), %esi
>> movl 8(%esp), %edi
>> movl %ebp, %esp
>> popl %ebp
>> ret
>> .size t, .-t
>> .comm a,8,8
>> .ident "GCC: (GNU) 4.4.3 20100127 (Red Hat 4.4.3-4)"
>> .section .note.GNU-stack,"",@progbits
>>
>>
>
