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Re: [Xen-devel] [Minios-devel] Excited for Xen Project in Outreachy

Hi Kanika,

On 22 Feb 2018, at 20:34, KANIKA SAINI <kanika16047@xxxxxxxxxxx> wrote:

Issue suggested by Simon
In Unikraft - whenever compiler flags are changed due to an addition of a library or something else according to the build rules, the make command doesn't force recompilation of those files affected by the flag change unless the files are altered too. The only way out is to "make clean" and "make" again all the files which can be redundantly time-consuming.

One way is to create flag files for objects and add those as their dependency in the Makefile.

Apart from this, I'm wondering if rules are passed on to the Makefile and changes are depicted in the Makefile itself, can we add Makefile as the dependency of objects to solve this issue?

I think the answer is in the documentation, which explains the UI (if you to call it that way) for the build system (see http://unikraft.neclab.eu/developers-app.html)

You can also usually figure out which parameters are passed to make via the command line by searching for the origin function, in particular for "command line" return values (https://www.gnu.org/software/make/manual/html_node/Origin-Function.html). This will give you a sense of the values that can be passed to the build system from outside of a makefile.

Now, you do need to make sure that you don't change the UI interface, as this would break everyone who uses Unikraft.

Assuming that all the flags we care about are already encoded in a Makefile (and don't come through the command line or through any other means), then adding a dependency may be sufficient. There is the question how granular you want this to be: 
a) Is it OK for everything to be rebuilt when say you change a -Dfoo 
b) Do you want this to be more fine grained

Have a google for something like "rebuilding when makefile flags change" and you will find a few example patterns with different trade-offs to solve this problem in general

The second challenge is that most substantial build rules get created dynamically via [unikraft/unikraft.git] / support / build / * 
Thus, adding a dependency on a makefile may not be as simple as it sounds

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