[PING][PATCH] Refactor debug routines.

[Ondřej Bílka]

On Wed, Oct 23, 2013 at 01:15:56AM +0200, Ondřej Bílka 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>
> 
> 
>