Bug #1528

ktrace does not show proper return values for pipe(2)

Added by corecode over 3 years ago. Updated over 3 years ago.

Status:New Start date:
Priority:Normal Due date:
Assignee:- % Done:

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Description

When ktracing a pipe syscall, the output is:

57705 a.out CALL pipe
57705 a.out RET pipe 3

However, the return value of pipe is 0, and the returned value for the
file descs is {3, 4}.

Related todos

History

#1
Updated by Beket over 3 years ago

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

#2
Updated by corecode over 3 years ago

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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