DragonFlyBSD

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)

Stathis

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_fds⁰ and sysmsg_fds¹. 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