Re: system call library functions

On Nov 29, 2004, at 1:06 PM, Dow Street wrote:



> All,
>
> I am writing some benchmarking code for OS X 10.3.5. When using  
> getpid() to measure the overhead of a system call, I find the overhead  
> to be much less than expected (1-3 clicks on the MPC 7447a TBR). When  
> making the call using syscall(20), however, the measurement is as  
> expected (~33 clicks on the TBR). Is getpid actually using a library  
> function which retrieves the PID from a user space data structure  
> (without entry into the kernel?)
Yes

> Any idea what / where this function
<http://www.opensource.apple.com/darwinsource/10.3.5/Libc-320.1.3/ppc/ 
sys/getpid.s>

> is located and the data structure it's accessing?
>
[ssen@localhost]$ nm -ma -s __DATA __data /usr/lib/libSystem.B.dylib |  
grep __current_pid
a00020a8 (__DATA,__data) external __current_pid

Shantonu