linux-kernel - Re: [PATCH] binfmt_flat: minimum support for the Blackfin relocations

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Date:	Sat, 29 Sep 2007 01:48:31 +0200
From:	Bernd Schmidt <bernds_cb1@...nline.de>
To:	Andrew Morton <akpm@...ux-foundation.org>
CC:	bryan.wu@...log.com, davidm@...pgear.com, gerg@...pgear.com,
	linux-kernel@...r.kernel.org,
	uclinux-dist-devel@...ckfin.uclinux.org
Subject: Re: [PATCH] binfmt_flat: minimum support for the Blackfin relocations

Andrew Morton wrote:
>>  	if (rev > OLD_FLAT_VERSION) {
>> +		unsigned long persistent = 0;
> 
> `persistent' here only has meaning inside the next nesting level, so should
> be moved down into that scope for readability reasons.

See below.

>> +			if (flat_set_persistent (relval, &persistent))
>> +				continue;
> 
> If this correct?  flat_set_persistent() returns zero if it didn't write
> anything to `persistent'.  It seems strange that in the case where
> flat_set_persistent() _does_ write something to `persistent', we just throw
> it away by doing `continue'.
> 
> Either that, or I've misread the code and you really did mean to put
> `persistent' in the outer scope, and its value is supposed to propagate
> over into the next iteration of the loop.  If so, that's all a bit too
> tricky for it to be implemented with zero code comments, dontcha think?

The latter.  We need to be able to use more data than we can fit into a 
single reloc, so we store a value with one reloc and reuse it with the 
next.  There'd be no point in having this function otherwise since you 
could perform whatever needs to be done in flat_get_relocate_addr.

This seemed fairly obvious at the time... when you're familiar with the 
flat format, the loop isn't all that hard to understand.  I'll add 
comments in the next version.


Bernd
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