Re: [PATCH] mmc: USB SDIO/SD/MMC Host Controller (VUB300) driver Resubmission

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On Mon, 24 Jan 2011, Tony Olech wrote:

> On Mon, 2011-01-24 at 10:55 -0500, Nicolas Pitre wrote:
> > On Mon, 24 Jan 2011, Tony Olech wrote:
> > 
> > > On Mon, 2011-01-24 at 09:43 -0500, Nicolas Pitre wrote:
> > > > Uninitialized global scope variables are by definition assigned to the 
> > > > .bss section.  The .bss section is dynamically allocated at run time 
> > > > rather than being stored in the compiled binary, and also cleared to 
> > > > zero at run time.  So the preference is for zero-initialized global 
> > > > variables not to be initialized at all because 1) they are implicitly 
> > > > initialized to zero anyway, and 2) that makes the resulting binaries 
> > > > smaller.
> > > > So this is not about fixing a bug, but rather to conform to the adopted 
> > > > policy for kernel code.
> > > > Nicolas
> > > Thanks for the reply. I had not realized that saving 20 bytes on the
> > > binary size was so important.
> > With the size of the kernel they add up.
> > > How then can one do static code analysis
> > > to determine which uninitialized variables are uninitialized as
> > > a result of a bug?
> > A good static code analysis tool should know already that uninitialized 
> > global variables are implicitly initialized to zero.  This is not the 
> > case for local variables of course
> > Nicolas
> Thanks for the reply.
> I had assumed that for a module the global initialized variables were
> loaded at module load. That then is a problem given that new devices
> (and drivers) are appearing quite rapidly. I therefore do not understand
> how the global initialized variables from an externally compiled kernel
> module get added into the kernel image - does "depmod" do that?


Sorry... I don't follow you here.

> A good static code analysis tool surely can only show a list of
> uninitialized static global variables leaving it for the user to
> trawl through and decide which are OK and which are not

Why?  Uninitialized static global variables should be assumed to be 
initialized to zero.  This is part of the C standard.  Nothing wrong 
here.  And the kernel coding style simply pushes it further by 
requesting it.


Nicolas
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