[ccache] Problem with using ccache during kernel compilation

[Andrew Stubbs]

On 15/01/14 16:16, Piotr Kiszka wrote:
 > I am trying to use ccache during kernel building.But there is always
 > zero cache hits during second kernel compilation:

I've observed this also. It's annoying!

The problem seems to be something in the way the kernel config 
autogenerates the header files. I did find out what it was, but I've 
forgotten now.

In fact, if you build the kernel, then delete all the .o files, and then 
run make again, you *do* get cache hits. "make clean" might be OK too, 
I'm not sure. Only if you start from completely clean, or reconfigure, 
then it doesn't work. Of course, this is the usual use case.

I don't recall finding a workable solution.

Sorry.

Andrew

P.s. A nice feature for ccache would be for it to report *why* a cached 
result wasn't found. This would only be meaningful in direct-mode, but 
still might be helpful. In preprocessor mode, *I* might find a list of 
hashes useful, so I could compare between runs, but this wouldn't be 
universally helpful, I suspect.