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[PING^2][PATCH] Refactor debug routines.


ping
On Wed, Oct 30, 2013 at 04:11:53PM +0100, OndÅej BÃlka wrote:
> On Wed, Oct 23, 2013 at 01:15:56AM +0200, OndÅej BÃlka wrote:
> > Hi,
> > 
> > After I looked at generic and x86-64 code I found following problems.
> > a) Performance. Performance of checking memset_chk and memcpy_chk is 
> > comparable to nonchecking ones. A strcpy_chk on benchtests is much
> > slower than stupid variant. Other functions are also slow because debug
> > has often byte-by-byte implementation.
> > b) Extensibility. Adding overlap checks is easier to add in c than
> > assembly.
> > 
> > A solution is to write functions in style of bounds check followed by
> > jump to corresponding routine. 
> > This should produce identic assembly as assembly files in ideal case, 
> > unfortunately gcc (or our annotations) contains a bug and does not issue
> > tailcall. Code for memset is following
> > 
> > 0000000000000000 <__memset_chk>:
> >    0:	48 83 ec 08          	sub    $0x8,%rsp
> >    4:	48 39 d1             	cmp    %rdx,%rcx
> >    7:	72 09                	jb     12 <__memset_chk+0x12>
> >    9:	48 83 c4 08          	add    $0x8,%rsp
> >    d:	e9 00 00 00 00       	jmpq   12 <__memset_chk+0x12>
> >   12:	e8 00 00 00 00       	callq  17 <__memset_chk+0x17>
> > 
> > 
> > 

-- 

Of course it doesn't work. We've performed a software upgrade.


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