Re: [Qemu-devel] [PATCH] make: explicit dependencies for ACPI gen sources

[Victor Kaplansky]

> ----- Original Message -----
> From: "Michael S. Tsirkin" <address@hidden>
> To: "Paolo Bonzini" <address@hidden>
> Cc: "Victor Kaplansky" <address@hidden>, address@hidden, "Richard Henderson" 
> <address@hidden>, "Eduardo Habkost" <address@hidden>
> Sent: Wednesday, August 5, 2015 4:59:56 PM
> Subject: Re: [PATCH] make: explicit dependencies for ACPI gen sources
> 
> On Wed, Aug 05, 2015 at 11:50:54AM +0200, Paolo Bonzini wrote:
> > 
> > 
> > On 04/08/2015 18:21, Victor Kaplansky wrote:
> > > Rebuilding QEMU after switching versions from git can cause make failure
> > > if IASL is enabled. This is caused by including stale *.d info from
> > > previous build.
> > > 
> > > To prevent this in the future we generate dependency info for generated
> > > ACPI sources in *.dep instead regular *.d and include them explicitly.
> > > This will allow us not to break future builds when one of such generated
> > > sources is removed - by removing explicit include of removed dependency.
> > > 
> > > By itself this doesn't fix broken builds from the past and this will be
> > > done by the following patch.
> > 
> > Does this happen the same way if you are removing a .c file?  If not,
> > can the same solution be used for .c and .dsl files?
> > 
> > Paolo
> 
> The problem is with .hex, not with .dsl files.
> It will happen with .c or .h file as well if .c/.h file is generated.

Right, if a foo.c is generated and has its own includes like foo.h, our rules
will automatically create dependency file foo.d:

foo.c: foo.h

foo.h

After you switch to a later commit which has removed foo.c (and all its 
sources), foo.d will be still there in the build tree and as we load all *.d 
files, foo.d will be loaded as well and this will break the build. It is
because foo.c has prerequisites, so make has to recreate it.  

I'm preparing another patch which will clean up the things, and will solve
the issue both for future commits and between old commits and new commits.
Switching between old commits will remain broken though.

-- Victor