DragonFly BSD
DragonFly bugs List (threaded) for 2009-10
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Re: [issue1528] ktrace does not show proper return values for pipe(2)

From: "Simon 'corecode' Schubert" <corecode@xxxxxxxxxxxx>
Date: Fri, 30 Oct 2009 19:36:58 +0100

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.


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