On this day, September 1, 2021, thus sayeth Greg KH: > On Wed, Sep 01, 2021 at 05:34:36PM +0200, Krish Jain wrote: > > > > Can you tell me why this is the case? > > Again, it depends on your kernel configuration file as to what will, or > will not, be built. > > If you have some things set as modules, they can be built as a module, > but the ashmem code can not be built as a module, so you would never > build it if you did the above line. > > Here, look at this sequence, starting with a tree that does nothing if I > do a simple 'make' in it, as the whole kernel is already built, and > ashmem is enabled in the kernel configuration > > $ grep ASHMEM .config > CONFIG_ASHMEM=y > $ make > $ > > So, let's change the time stamp on the ashmem.c file and see what gets > built if you use the M= option: > > $ touch drivers/staging/android/ashmem.c > $ make M=drivers/staging/android > MODPOST drivers/staging/android/Module.symvers > $ > > Nothing gets built as ashmem is NOT a module, and M= only builds any > modules in the directory you specified. > > But, if you tell make to just build the whole subdirectory, no matter > what the setting is, it will be built: > > $ make drivers/staging/android/ > CALL scripts/checksyscalls.sh > CALL scripts/atomic/check-atomics.sh > DESCEND objtool > CC drivers/staging/android/ashmem.o > AR drivers/staging/android/built-in.a > $ > > So that's the difference, "M=" builds modules in that directory, but if > you tell it to build the subdir, everything in there that needs to be > built, will be built. > > Be careful about your kernel configuration, that is the key for what > will, and will not, be built. > Ouch... I want to *really* apologize to you Krish for introducing so much confusion while you, and apparently I, am still learning. And for your persistence with seeking the correct answer here Krish. I did not notice that this could only be build as a built-in object. Thank you Greg for pointing out my mistake, and I apologize for dragging this out longer than it had to and the frustration this caused. It seems I will be reading the documentation again, along with Greg's book recommendation, "Linux Kernel in a Nutshell" over this merge window. Thank you again Krish and Greg ~Bryan
