Re: [issue1528] ktrace does not show proper return values for pipe(2)

["Simon 'corecode' Schubert" <corecode@xxxxxxxxxxxx>]

Stathis Kamperis (via DragonFly issue tracker) wrote:
> Stathis Kamperis <ekamperi@gmail.com> added the comment:
>
> I've added a kprintf in ktrsysret() and here is what printed:
>
> 1126 a.out   CALL pipe
> 1126 a.out   RET  ret=3 error=0 code=42 pipe 3
>
> Question is why `ret' contains the first file descriptor of the pair at all.
> (and not zero as ought to)

This is because sys_pipe returns both fds as return value, namely 
sysmsg_fds[0] and sysmsg_fds[1].  However ktrsysret is only called with 
sysmsg_result, which covers only the first fd.

I guess the pipe libc glue code copies this result into the array.

cheers
  simon

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