Messages in this thread | | | Date | Mon, 27 Mar 2006 16:06:06 +0200 | From | Sam Ravnborg <> | Subject | Re: Build system runs ld more often than needed |
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On Mon, Mar 27, 2006 at 02:38:48PM +0200, Jean Delvare wrote: > Hi Sam, > > I have noticed the following problem: > > khali@arrakis:~/src/linux-2.6.16-git> make modules > CHK include/linux/version.h > Building modules, stage 2. > MODPOST > khali@arrakis:~/src/linux-2.6.16-git> touch drivers/media/video/zoran_card.c > khali@arrakis:~/src/linux-2.6.16-git> make modules > CHK include/linux/version.h > CC [M] drivers/media/video/zoran_card.o > LD [M] drivers/media/video/zr36067.o > LD [M] drivers/media/video/msp3400.o > LD [M] drivers/media/video/tuner.o > Building modules, stage 2. > MODPOST > LD [M] drivers/media/video/msp3400.ko > LD [M] drivers/media/video/tuner.ko > LD [M] drivers/media/video/zr36067.ko > khali@arrakis:~/src/linux-2.6.16-git> > > See how unrelated modules are linked again?
This is an unfortunate side-effect. Following snippet from scripts/Makfile.build explains it:
# We would rather have a list of rules like # foo.o: $(foo-objs) # but that's not so easy, so we rather make all composite objects depend # on the set of all their parts $(multi-used-y) : %.o: $(multi-objs-y) FORCE $(call if_changed,link_multi-y)
The problem is that we have no easy way to say that this specific module depends on this list of .o files. With make 3.81 this would be possible utilising $(eval ...), but the benefit is too low to introduce such a dependency.
> > I investigated further and it seems to happen whenever a given Makefile > has more than one composite object definition. In the case of > drivers/media/video, the following composite objects are defined: > > zoran-objs := zr36120.o zr36120_i2c.o zr36120_mem.o > zr36067-objs := zoran_procfs.o zoran_device.o \ > zoran_driver.o zoran_card.o > tuner-objs := tuner-core.o tuner-types.o tuner-simple.o \ > mt20xx.o tda8290.o tea5767.o > > msp3400-objs := msp3400-driver.o msp3400-kthreads.o > > I have the following enabled: > > CONFIG_VIDEO_MSP3400=m > CONFIG_VIDEO_ZORAN=m > CONFIG_VIDEO_TUNER=m > > So msp3400 and tuner are relinked whenever I make a change to the > zr36067 driver.
You could do: make drivers/media/video/zr36067.ko to avoid linking the others.
But kbuild will unfortunately link to much modules for a normal build.
One day I may try to generate one big Makefile and then it could be addressed but I have yet to find 'the' reason to invest time in that task.
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