[Qemu-devel] [PATCH] CPPFLAGS+= in Makefile.target

[Qemu-devel] [PATCH] CPPFLAGS+= in Makefile.target

[Ian Jackson]

Saying CPPFLAGS+= is much more convenient if for any reason the
external build environment would like to pass unusual CPPFLAGS.

Regards,
Ian.

Index: Makefile.target
===================================================================
RCS file: /sources/qemu/qemu/Makefile.target,v
retrieving revision 1.240
diff -u -r1.240 Makefile.target
--- Makefile.target	14 Jan 2008 22:09:11 -0000	1.240
+++ Makefile.target	25 Jan 2008 14:16:24 -0000
@@ -24,7 +24,7 @@
 endif
 TARGET_PATH=$(SRC_PATH)/target-$(TARGET_BASE_ARCH)
 VPATH=$(SRC_PATH):$(TARGET_PATH):$(SRC_PATH)/hw
-CPPFLAGS=-I. -I.. -I$(TARGET_PATH) -I$(SRC_PATH) -MMD -MP -DNEED_CPU_H
+CPPFLAGS+=-I. -I.. -I$(TARGET_PATH) -I$(SRC_PATH) -MMD -MP -DNEED_CPU_H
 ifdef CONFIG_DARWIN_USER
 VPATH+=:$(SRC_PATH)/darwin-user
 CPPFLAGS+=-I$(SRC_PATH)/darwin-user -I$(SRC_PATH)/darwin-user/$(TARGET_ARCH)

Re: [Qemu-devel] [PATCH] CPPFLAGS+= in Makefile.target

[Paul Brook]

> Saying CPPFLAGS+= is much more convenient if for any reason the
> external build environment would like to pass unusual CPPFLAGS.

No. This doesn't do what you thing it does.
The most common way of overriding these variables is to pass them on the 
commandline, i.e. "make CPPFLAGS=-blah". This overrides all assignments to 
that variable including +=.

Paul

Re: [Qemu-devel] [PATCH] CPPFLAGS+= in Makefile.target

[Ian Jackson]

Paul Brook writes ("Re: [Qemu-devel] [PATCH] CPPFLAGS+= in Makefile.target"):
> No. This doesn't do what you thing it does.
> The most common way of overriding these variables is to pass them on the 
> commandline, i.e. "make CPPFLAGS=-blah". This overrides all assignments to 
> that variable including +=.

Err, yes (and this is annoying behaviour in make), but if
Makefile.target sets CPPFLAGS=-I... then even config.mak cannot
override it.

Ian.

Re: [Qemu-devel] [PATCH] CPPFLAGS+= in Makefile.target

[Ian Jackson]

iwj writes ("Re: [Qemu-devel] [PATCH] CPPFLAGS+= in Makefile.target"):
> Paul Brook writes ("Re: [Qemu-devel] [PATCH] CPPFLAGS+= in Makefile.target"):
> > No. This doesn't do what you thing it does.
> > The most common way of overriding these variables is to pass them on the 
> > commandline, i.e. "make CPPFLAGS=-blah". This overrides all assignments to 
> > that variable including +=.
> 
> Err, yes (and this is annoying behaviour in make), but if
> Makefile.target sets CPPFLAGS=-I... then even config.mak cannot
> override it.

Sorry, perhaps that was less than clear.  What I mean is: if you want
for any reason to build qemu in a weird way then you're going to have
to edit config-host.mak (or somewhere similar) in any case.  You
probably want to set some CPPFLAGS as well as various other things.
If you do this at the moment then you have to reproduce all of the
CPPFLAGS -I settings and so on from Makefile.target in your own
setting that you add to config-host.mak.

With my change this is no longer needed: if you set CPPFLAGS in
config-host.mak or some target's config.mak then the right -I's are
automatically added later.

Ian.

Re: [Qemu-devel] [PATCH] CPPFLAGS+= in Makefile.target

[Paul Brook]

> What I mean is: if you want
> for any reason to build qemu in a weird way then you're going to have
> to edit config-host.mak (or somewhere similar) in any case.  You
> probably want to set some CPPFLAGS as well as various other things.
> If you do this at the moment then you have to reproduce all of the
> CPPFLAGS -I settings and so on from Makefile.target in your own
> setting that you add to config-host.mak.

In that case you should always provide a definition in config-host.mak.
Under some circumstances make may inherit initial values from elsewhere.
The rules for make variables are sufficiently twisty that it's best to be 
explicit, rather than allowing a subset of the ways of defining that 
variable.


Paul

Re: [Qemu-devel] [PATCH] CPPFLAGS+= in Makefile.target

[Ian Jackson]

Paul Brook writes ("Re: [Qemu-devel] [PATCH] CPPFLAGS+= in Makefile.target"):
> In that case you should always provide a definition in config-host.mak.
> Under some circumstances make may inherit initial values from elsewhere.

What circumstances ?  CPPFLAGS+= overrides (discards) values in the
environment as well as ones from the command line.

Providing a definition in config-host.mak involves duplicating the
value, which can't be right.  If there's no other way to do it then
there should be a reference to USER_CPPFLAGS or some such but frankly
that's a pain and overkill.

Ian.

Re: [Qemu-devel] [PATCH] CPPFLAGS+= in Makefile.target

[Paul Brook]

On Friday 25 January 2008, Ian Jackson wrote:
> Paul Brook writes ("Re: [Qemu-devel] [PATCH] CPPFLAGS+= in 
Makefile.target"):
> > In that case you should always provide a definition in config-host.mak.
> > Under some circumstances make may inherit initial values from elsewhere.
>
> What circumstances ?  CPPFLAGS+= overrides (discards) values in the
> environment as well as ones from the command line.

$ cat Makefile
FOO += World
all:
        @echo "$(FOO)"
$ FOO=Hello make
Hello World

Re: [Qemu-devel] [PATCH] CPPFLAGS+= in Makefile.target

[Ian Jackson]

Paul Brook writes ("Re: [Qemu-devel] [PATCH] CPPFLAGS+= in Makefile.target"):
> On Friday 25 January 2008, Ian Jackson wrote:
> > What circumstances ?  CPPFLAGS+= overrides (discards) values in the
> > environment as well as ones from the command line.
> 
> [ demonstration ]

Oh, err, looks like I messed up in my own test.  I see what you mean.
We don't want the top-level's CPPFLAGS turning up there.

Still, there ought to be a way to introduce extra compiler options
that doesn't involve duplicating the ones which are essential to find
qemu's own includes etc.

Ian.

Re: [Qemu-devel] [PATCH] CPPFLAGS+= in Makefile.target

[Paul Brook]

> Providing a definition in config-host.mak involves duplicating the
> value, which can't be right.  

Huh? No it doesn't. config-host.mak contains
CPPFLAGS=
then Makefile.target contains
CPPFLAGS+=whatever

> If there's no other way to do it then 
> there should be a reference to USER_CPPFLAGS or some such but frankly
> that's a pain and overkill.

Why don't you just put your custom flags in CFLAGS, not CPPFLAGS?
The former is deliberately left for the user to override.

Paul

Re: [Qemu-devel] [PATCH] CPPFLAGS+= in Makefile.target

[Ian Jackson]

Paul Brook writes ("Re: [Qemu-devel] [PATCH] CPPFLAGS+= in Makefile.target"):
> Huh? No it doesn't. config-host.mak contains
> CPPFLAGS=
> then Makefile.target contains
> CPPFLAGS+=whatever

It doesn't seem to on my build.

> Why don't you just put your custom flags in CFLAGS, not CPPFLAGS?
> The former is deliberately left for the user to override.

Several (but not all AFAICT) of the target subdirectory Makefiles set
CFLAGS.

Anyway, I think you're right that I should go away and think about
this some more.  Sorry for the inconvenience.

Ian.

Re: [Qemu-devel] [PATCH] CPPFLAGS+= in Makefile.target

[Paul Brook]

> > Why don't you just put your custom flags in CFLAGS, not CPPFLAGS?
> > The former is deliberately left for the user to override.
>
> Several (but not all AFAICT) of the target subdirectory Makefiles set
> CFLAGS.

Really? Which ones?

Paul

Re: [Qemu-devel] [PATCH] CPPFLAGS+= in Makefile.target

[Ian Jackson]

Paul Brook writes ("Re: [Qemu-devel] [PATCH] CPPFLAGS+= in Makefile.target"):
> Really? Which ones?

tests/Makefile and tests/cris/Makefile do.  Not that they're
particularly important.  I also saw Makefile.target's if'd out change
to CFLAGS near at the bottom by the audio .o's, but of course that's
not really relevant.

Ian.

Re: [Qemu-devel] [PATCH] CPPFLAGS+= in Makefile.target

[Ronan Keryell]

>>>>> On Fri, 25 Jan 2008 14:39:57 +0000, Paul Brook <paul@codesourcery.com> said:

    >> Saying CPPFLAGS+= is much more convenient if for any reason the
    >> external build environment would like to pass unusual CPPFLAGS.

    Paul> No. This doesn't do what you thing it does.  The most common way
    Paul> of overriding these variables is to pass them on the
    Paul> commandline, i.e. "make CPPFLAGS=-blah". This overrides all
    Paul> assignments to that variable including +=.

By the way, it is possible to improve the GNU make weirdness :-) by
playing with stuff like:

override CFLAGS += -g

Cf section 6.7 of the documentation.

Hmmm... GNU make evolves more rapidly than my brain... :-)
-- 
  Ronan KERYELL                 |\/  Tel:    (+33|0) 2.29.00.14.15
  Département Informatique      |/)  Fax:    (+33|0) 2.29.00.12.82
  TÉLÉCOM Bretagne, CS 83818    K    GSM:    (+33|0) 6.13.14.37.66
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Re: [Qemu-devel] [PATCH] CPPFLAGS+= in Makefile.target

[Thiemo Seufer]

Ronan Keryell wrote:
> >>>>> On Fri, 25 Jan 2008 14:39:57 +0000, Paul Brook <paul@codesourcery.com> said:
> 
>     >> Saying CPPFLAGS+= is much more convenient if for any reason the
>     >> external build environment would like to pass unusual CPPFLAGS.
> 
>     Paul> No. This doesn't do what you thing it does.  The most common way
>     Paul> of overriding these variables is to pass them on the
>     Paul> commandline, i.e. "make CPPFLAGS=-blah". This overrides all
>     Paul> assignments to that variable including +=.
> 
> By the way, it is possible to improve the GNU make weirdness :-) by
> playing with stuff like:
> 
> override CFLAGS += -g
> 
> Cf section 6.7 of the documentation.

IIRC the documentation warns against careless use of overrides.

> Hmmm... GNU make evolves more rapidly than my brain... :-)

It's only a decade old or so. :-)


Thiemo