Re: [Xen-devel] [PATCH for-4.7] docs/build: Work around apparent bug with multi-target rules

[Wei Liu <wei.liu2@xxxxxxxxxx>]

On Mon, Apr 25, 2016 at 02:35:56PM +0100, Ian Jackson wrote:
> Andrew Cooper writes ("[PATCH for-4.7] docs/build: Work around apparent bug 
> with multi-target rules"):
> > The `make` manual documents that a rule of the form
> > 
> >   target1 target2: prereq
> >     recipe
> > 
> > is equivilent to
> > 
> >   target1: prereq
> >     recipe
> >   target2: prereq
> >     recipe
> > 
> > This is correct if only target1 or target2 is wanted, but is not the
> > case if both target1 and target2 are wanted to be rebuilt in the
> > same pass.  In such a case, executing the recipe to generate target1
> > causes the entire rule to be considered complete, short circuiting
> > the search to regenerate target2.
> 
> This is not a bug in make.  From the manual I have here (wheezy):
> 
>      Suppose you would like to vary the prerequisites according to the
>    target, much as the variable `$@' allows you to vary the commands.
>    You cannot do this with multiple targets in an ordinary rule, but
>    you can do it with a "static pattern rule".  *Note Static Pattern
>    Rules: Static Pattern.
> 
> and (from `Pattern Intro'):
> 
>      Pattern rules may have more than one target.  Unlike normal
>    rules, this does not act as many different rules with the same
>    prerequisites and commands.  If a pattern rule has multiple
>    targets, `make' knows that the rule's commands are responsible for
>    making all of the targets.  The commands are executed only once to
>    make all the targets.
> 
> So this is a bug in the Makefile.  Your patch looks like a right
> approach to me.  A static pattern rule would be the other option.
> 
> Acked-by: Ian Jackson <ian.jackson@xxxxxxxxxxxxx>
> 

Release-acked-by: Wei Liu <wei.liu2@xxxxxxxxxx>

Thank you both for handling this.

Andrew, I think you need to resubmit with updated subject line and
commit message.

Wei.

> Ian.

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