[PATCH] Makefile: do not optimize when DEBUG=1

[PATCH] Makefile: do not optimize when DEBUG=1

[Johannes Schindelin]

There is this wonderful debugger named gdb, which sometimes has severe
problems when the source is compiled with optimization. So, you have to
recompile (at least parts of the source) _without_ -O2 if you want to
have a chance to look at otherwise optimized-out variables.

You can do that now by removing just the object files containing the
code you want to debug, and saying "make DEBUG=1".

Signed-off-by: Johannes Schindelin <Johannes.Schindelin@gmx.de>
---
 Makefile |    7 ++++++-
 1 files changed, 6 insertions(+), 1 deletions(-)

diff --git a/Makefile b/Makefile
index c3d67af..18fdc5e 100644
--- a/Makefile
+++ b/Makefile
@@ -110,6 +110,8 @@ all::
 # Define NO_PERL_MAKEMAKER if you cannot use Makefiles generated by perl's
 # MakeMaker (e.g. using ActiveState under Cygwin).
 #
+# Define DEBUG=1 to compile without optimization.
+#
 
 GIT-VERSION-FILE: .FORCE-GIT-VERSION-FILE
 	@$(SHELL_PATH) ./GIT-VERSION-GEN
@@ -123,7 +125,10 @@ uname_P := $(shell sh -c 'uname -p 2>/dev/null || echo not')
 
 # CFLAGS and LDFLAGS are for the users to override from the command line.
 
-CFLAGS = -g -O2 -Wall
+CFLAGS = -g -Wall
+ifndef DEBUG
+	CFLAGS += -O2
+endif
 LDFLAGS =
 ALL_CFLAGS = $(CFLAGS)
 ALL_LDFLAGS = $(LDFLAGS)
-- 
1.5.0.3.2559.g30d3b

Re: [PATCH] Makefile: do not optimize when DEBUG=1

[Johannes Sixt]

Johannes Schindelin wrote:
> You can do that now by removing just the object files containing the
> code you want to debug, and saying "make DEBUG=1".
> [...]
> -CFLAGS = -g -O2 -Wall
> +CFLAGS = -g -Wall
> +ifndef DEBUG
> +       CFLAGS += -O2
> +endif

I think the shortcut to remove just the interesting object file does not
work because Makefile notices (the GIT-CFLAGS rule) that there are "new
flags or prefix", and so recompiles everything.

-- Hannes

Re: [PATCH] Makefile: do not optimize when DEBUG=1

[Johannes Schindelin]

Hi,

On Wed, 7 Mar 2007, Johannes Sixt wrote:

> Johannes Schindelin wrote:
> > You can do that now by removing just the object files containing the
> > code you want to debug, and saying "make DEBUG=1".
> > [...]
> > -CFLAGS = -g -O2 -Wall
> > +CFLAGS = -g -Wall
> > +ifndef DEBUG
> > +       CFLAGS += -O2
> > +endif
> 
> I think the shortcut to remove just the interesting object file does not 
> work because Makefile notices (the GIT-CFLAGS rule) that there are "new 
> flags or prefix", and so recompiles everything.

That is unfortunatley true, and was hidden in my test by something 
completely unrelated.

I do something completely different now:

@@ -846,7 +841,8 @@ TRACK_CFLAGS = $(subst ','\'',$(ALL_CFLAGS)):\
 
 GIT-CFLAGS: .FORCE-GIT-CFLAGS
 	@FLAGS='$(TRACK_CFLAGS)'; \
-	    if test x"$$FLAGS" != x"`cat GIT-CFLAGS 2>/dev/null`" ; then \
+	    if test x"$$FLAGS" != x"`cat GIT-CFLAGS 2>/dev/null`" -a \
+		    -z "$(IGNORE_GIT_CFLAGS)"; then \
 		echo 1>&2 "    * new build flags or prefix"; \
 		echo "$$FLAGS" >GIT-CFLAGS; \
             fi

... and in my config.mak, there is

ifdef DEBUG
	ALL_CFLAGS := $(filter-out -O2,$(ALL_CFLAGS))
	IGNORE_GIT_CFLAGS = YesPlease
endif

I'm happy now.

Ciao,
Dscho

[PATCH] Avoid rebuilding everything if user changes CFLAGS on the make command line

[Johannes Sixt]

From: Johannes Sixt <johannes.sixt@telecom.at>

The following sequence of commands is commonly used to recompile
selected files with different flags, for example, to change the debug
information:

   make
   rm builtin-diff.o
   make CFLAGS="-g -O0"

However, the Makefile is clever enough to notice that the second 'make'
invocation changes the build flags and rebuilds everything.

This change exempts the value of CFLAGS (which is explicitly declared
as reserved for the user to change from the command line) from this
auto-detection.

Signed-off-by: Johannes Sixt <johannes.sixt@telecom.at>
---
Johannes Schindelin wrote:
>  GIT-CFLAGS: .FORCE-GIT-CFLAGS
>         @FLAGS='$(TRACK_CFLAGS)'; \
> -           if test x"$$FLAGS" != x"`cat GIT-CFLAGS 2>/dev/null`" ; then \
> +           if test x"$$FLAGS" != x"`cat GIT-CFLAGS 2>/dev/null`" -a \
> +                   -z "$(IGNORE_GIT_CFLAGS)"; then \
>                 echo 1>&2 "    * new build flags or prefix"; \
>                 echo "$$FLAGS" >GIT-CFLAGS; \
>              fi

IMHO, the value of $(CFLAGS) (which the Makefile declares as "for the
users to override from the command line") should never take part in this
build-flags-change-autodetection.

-- Hannes

 Makefile |    2 +-
 1 files changed, 1 insertions(+), 1 deletions(-)

diff --git a/Makefile b/Makefile
index 9a37b15..8410530 100644
--- a/Makefile
+++ b/Makefile
@@ -812,7 +812,7 @@ tags:
 	find . -name '*.[hcS]' -print | xargs ctags -a
 
 ### Detect prefix changes
-TRACK_CFLAGS = $(subst ','\'',$(ALL_CFLAGS)):\
+TRACK_CFLAGS = $(subst ','\'',$(BASIC_CFLAGS)):\
             
$(bindir_SQ):$(gitexecdir_SQ):$(template_dir_SQ):$(prefix_SQ)
 
 GIT-CFLAGS: .FORCE-GIT-CFLAGS
-- 
1.5.0.2.279.g4808

Re: [PATCH] Avoid rebuilding everything if user changes CFLAGS on the make command line

[Junio C Hamano]

Johannes Sixt <J.Sixt@eudaptics.com> writes:

> IMHO, the value of $(CFLAGS) (which the Makefile declares as "for the
> users to override from the command line") should never take part in this
> build-flags-change-autodetection.

This on the surface looks nicer than the other Johannes's
approach, but I have reservations.  The user can always say
"make CFLAGS=-DNO_SYNLINK_HEAD=NoThanks" from the command line
to affect the behaviour, and in such a case this approach
breaks.

As long as you declare CFLAGS is there for users to override
only the way the programs are compiled (e.g. optimization) and
it is forbidden to use CFLAGS to affect the way the programs are
to behave (iow, "use of -D<FEATURE> in CFLAGS is forbidden"), it
would be Ok, but in effect it is forcing people to modify
config.mak even for "try out this configuration just this time,
one-shot" compilation, which makes me somewhat unhappy.

IGNORE_GIT_CFLAGS looks much uglier, but is much nicer from
design standpoint.  At least the user declares "I know what I am
doing, and I assume full responsibility".  That might be less
confusing in the end.

Undecided.