Xen devel - Jul 2010 - [PATCH] correct order of linker options to avoid link errors with recent toolchains

The order of objects and linked libraries is important with recent toolchain
when --as-needed is used. Move LDFLAGS to the end of cc commandline options.
Without this change, symbols in libbzip2 are not found when building with
openSuSE 11.2 and newer.

Signed-off-by: Olaf Hering <olaf@aepfle.de>

---

There are more places like this.
I will find and fix them when required.

 tools/libxc/Makefile |    2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

--- xen-unstable.hg-4.1.21836.orig/tools/libxc/Makefile
+++ xen-unstable.hg-4.1.21836/tools/libxc/Makefile
@@ -181,7 +181,7 @@ xc_dom_bzimageloader.opic: CFLAGS += $(c
 
 libxenguest.so.$(MAJOR).$(MINOR): LDFLAGS += $(call zlib-options,l)
 libxenguest.so.$(MAJOR).$(MINOR): $(GUEST_PIC_OBJS) libxenctrl.so
-	$(CC) $(CFLAGS) $(LDFLAGS) -Wl,$(SONAME_LDFLAG) -Wl,libxenguest.so.$(MAJOR)
$(SHLIB_CFLAGS) -o $@ $(GUEST_PIC_OBJS) -lz -lxenctrl $(PTHREAD_LIBS)
+	$(CC) $(CFLAGS) -Wl,$(SONAME_LDFLAG) -Wl,libxenguest.so.$(MAJOR)
$(SHLIB_CFLAGS) -o $@ $(GUEST_PIC_OBJS) $(LDFLAGS) -lz -lxenctrl $(PTHREAD_LIBS)
 
 -include $(DEPS)
 

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Olaf Hering writes ("[Xen-devel] [PATCH] correct order of linker options to
avoid link errors with recent toolchains"):
> The order of objects and linked libraries is important with recent
toolchain
> when --as-needed is used. Move LDFLAGS to the end of cc commandline
options.
> Without this change, symbols in libbzip2 are not found when building with
openSuSE 11.2 and newer.
Thanks, but:

I infer that libbzip2 is in LDFLAGS (as -lbzip2, I guess).  Is that
right ?  But I think that libraries should be in *_LIBS, not LDFLAGS.
LDFLAGS needs to stay at the beginning so that it can work if you set
it to -static or something.
>  libxenguest.so.$(MAJOR).$(MINOR): LDFLAGS += $(call zlib-options,l)
What is this program "zlib-options" ?  I don''t have it on my
system.

Ian.

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On 23/07/2010 17:44, "Ian Jackson" <Ian.Jackson@eu.citrix.com>
wrote:
> Olaf Hering writes ("[Xen-devel] [PATCH] correct order of linker
options to
> avoid link errors with recent toolchains"):
>> The order of objects and linked libraries is important with recent
toolchain
>> when --as-needed is used. Move LDFLAGS to the end of cc commandline
options.
>> Without this change, symbols in libbzip2 are not found when building
with
>> openSuSE 11.2 and newer.
> 
> Thanks, but:
> 
> I infer that libbzip2 is in LDFLAGS (as -lbzip2, I guess).  Is that
> right ?  But I think that libraries should be in *_LIBS, not LDFLAGS.
> LDFLAGS needs to stay at the beginning so that it can work if you set
> it to -static or something.
> 
>>  libxenguest.so.$(MAJOR).$(MINOR): LDFLAGS += $(call zlib-options,l)
> 
> What is this program "zlib-options" ?  I don''t have it
on my system.
It''s right there in the same Makefile directly above the line you
quoted.
Yes, the above line can add -l<lib> items to LDFLAGS. Sounds like the
right
fix would indeed be to define a new COMPRESSION_LIBS variable and put it at
the end of the linker command line.

 -- Keir



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Keir Fraser writes ("Re: [Xen-devel] [PATCH] correct order of linker
options to avoid link errors with recent
toolchains"):
> On 23/07/2010 17:44, "Ian Jackson"
<Ian.Jackson@eu.citrix.com> wrote:
> >>  libxenguest.so.$(MAJOR).$(MINOR): LDFLAGS += $(call
zlib-options,l)
> > 
> > What is this program "zlib-options" ?  I don''t have
it on my system.
> 
> It''s right there in the same Makefile directly above the line you
quoted.
> Yes, the above line can add -l<lib> items to LDFLAGS.
Oh, duh.  I''m confusing $(call ...) with $(shell ...) so I looked in
entirely the wrong place.
>  Sounds like the right fix would indeed be to define a new
> COMPRESSION_LIBS variable and put it at the end of the linker
> command line.
Yes.  Olaf, would you like to provide a patch to do that ?

Ian.

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The order of objects and linked libraries is important with recent toolchain
when --as-needed is used.
Introduce new variable COMPRESSION_LIBS and place it at the end of cc
commandline options.
Without this change, symbols in libbzip2 are not found when building with
openSuSE 11.2 and newer.

Signed-off-by: Olaf Hering <olaf@aepfle.de>

---
v2: use COMPRESSION_LIBS instead of moving LDFLAGS around

 tools/libxc/Makefile |    4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

--- xen-unstable.hg-4.1.21836.orig/tools/libxc/Makefile
+++ xen-unstable.hg-4.1.21836/tools/libxc/Makefile
@@ -179,9 +179,9 @@ endif
 xc_dom_bzimageloader.o: CFLAGS += $(call zlib-options,D)
 xc_dom_bzimageloader.opic: CFLAGS += $(call zlib-options,D)
 
-libxenguest.so.$(MAJOR).$(MINOR): LDFLAGS += $(call zlib-options,l)
+libxenguest.so.$(MAJOR).$(MINOR): COMPRESSION_LIBS = $(call zlib-options,l)
 libxenguest.so.$(MAJOR).$(MINOR): $(GUEST_PIC_OBJS) libxenctrl.so
-	$(CC) $(CFLAGS) $(LDFLAGS) -Wl,$(SONAME_LDFLAG) -Wl,libxenguest.so.$(MAJOR)
$(SHLIB_CFLAGS) -o $@ $(GUEST_PIC_OBJS) -lz -lxenctrl $(PTHREAD_LIBS)
+	$(CC) $(CFLAGS) $(LDFLAGS) -Wl,$(SONAME_LDFLAG) -Wl,libxenguest.so.$(MAJOR)
$(SHLIB_CFLAGS) -o $@ $(GUEST_PIC_OBJS) $(COMPRESSION_LIBS) -lz -lxenctrl
$(PTHREAD_LIBS)
 
 -include $(DEPS)
 

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