[Dev] Setting dash as default shell (or getting rid of bash)

Thiago Macieira thiago.macieira at intel.com
Wed Oct 2 05:17:47 GMT 2013

On quarta-feira, 2 de outubro de 2013 12:32:47, Carsten Haitzler wrote:
> does cover it, but only briefly. it says that it "tries to compress the
> first part of a file and if that fails (eg isn't smaller) then it aborts
> compressing any more of that file at all". so what is this "first part"? is
> it 4k, 512 bytes? 128k? is it strictly "if compressed size less than
> original" eg if it compressed 4096 bytes to 4095 - it keeps compressing" or
> does the margin have to EXCEED some factor (eg 4000 bytes down from 4096 is
> not good enough. you have to get to 3500 to have compression kick in). so
> the page is a bit vague on how it figures it out.

Probably the answers to all those questions are "it varies according to the 
implementation and available CPU power".

> and then there comes the issue that... let's assume it's semi-smart and has
> some % threshold you have to hit - eg u have to get to < 80% of original
> size for header to begin to compress the rest... what happens to formats
> that have headers that compress well, but tails that just waste cpu time
> hand-over-fist to compress the rest?

I'd provide a tool that does off-line compression. Leave it to user-space to 
decide what files compress better as well as any techniques for compressing 
parts of the file and not others.

For example, it might be a good idea to compress only portions of ELF files: RW 
sections (lots of zeroes interspersed with non-zero data), .rodata (lots of 
string literals) and .rel.plt (PLT stubs are very similar to one another, 
changing usually a few bits from one stub to the next). 

Moreover, leaving the ELF header uncompressed and changing the linker to emit 
the sections necessary at load time together might be a good idea (why is the 
.dynamic section even writable?)

Thiago Macieira - thiago.macieira (AT) intel.com
  Software Architect - Intel Open Source Technology Center
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