[OE-core] Very large size of libraries in core-image-minimal rootfs

[Khem Raj]

On Mon, 2019-11-25 at 23:10 +0200, Adrian Bunk wrote:
> On Mon, Nov 25, 2019 at 07:26:58PM +0000, Ross Burton wrote:
> > On 25/11/2019 18:37, Ankur Tyagi wrote:
> > > Hi,
> > > 
> > > Based upon "thud" branch, I created core-image-minimal for
> > > am335x-evm
> > > board and resulting image size is very big(71M)
> > 
> > If disk size is important then a good first step is to use musl
> > instead of
> > glibc:
> > 
> > TCLIBC = "musl"
> > ...
> 
> musl is mainly useful for tiny systems, a 40 MB partition is such a
> huge
> amount of space that the size of the C library no longer matters
> much.
> 
> The size benefit of replacing glibc with musl is around 2 MB.

I would refrain from labeling as useful for tiny systems. since
static size is one thing, there is DRAM behaviour which is equally
important, how malloc and other resource oriented algorithms behave is
important as well.

secondly, if I have 40MB partition, one might rather want to use extra
space for implementing features in their product than spend it for
enabling the system if they can.

there are many other design considerations where musl might make more
sense

> 
> A partition with an -Os build of Yocto with glibc+systemd (sic)
> is around 9 MB, together with bootloader and kernel this all
> fits in a 16 MB flash. Use compression for kernel and root
> filesystem and everything fits in a 8 MB flash.
> 

-Os is not as well tested option as -O2 is. So we should always
recommend it with grain of salt, speaking from experience there are
bugs that will show up with Os which you wont see with O2 and leave a
bad taste for user

> > Ross
> 
> cu
> Adrian