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Re: [XEN PATCH] libs/util: Fix parallel build between flex/bison and CC rules
- To: Anthony PERARD <anthony.perard@xxxxxxxxxx>, xen-devel@xxxxxxxxxxxxxxxxxxxx
- From: Andrew Cooper <Andrew.Cooper3@xxxxxxxxxx>
- Date: Thu, 9 Feb 2023 14:03:22 +0000
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- Cc: Wei Liu <wl@xxxxxxx>, Juergen Gross <jgross@xxxxxxxx>
- Delivery-date: Thu, 09 Feb 2023 14:03:48 +0000
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- List-id: Xen developer discussion <xen-devel.lists.xenproject.org>
On 09/02/2023 12:11 pm, Anthony PERARD wrote:
> flex/bison generate two targets, and when those targets are
> prerequisite of other rules they are considered independently by make.
>
> We can have a situation where the .c file is out-of-date but not the
> .h, git checkout for example. In this case, if a rule only have the .h
Nit. s/have/has/
(Can fix on commit.)
> file as prerequiste, make will procced and start to build the object.
> In parallel, another target can have the .c file as prerequisite and
> make will find out it need re-generating and do so, changing the .h at
> the same time. This parallel task breaks the first one.
>
> To avoid this scenario, we put both the header and the source as
> prerequisite for all object even if they only need the header.
>
> Reported-by: Andrew Cooper <Andrew.Cooper3@xxxxxxxxxx>
> Signed-off-by: Anthony PERARD <anthony.perard@xxxxxxxxxx>
Acked-by: Andrew Cooper <andrew.cooper3@xxxxxxxxxx>
This is a very subtle corner case.
~Andrew
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