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[PING^3][PATCH] Refactor debug routines.
- From: OndÅej BÃlka <neleai at seznam dot cz>
- To: libc-alpha at sourceware dot org
- Date: Tue, 26 Nov 2013 20:20:13 +0100
- Subject: [PING^3][PATCH] Refactor debug routines.
- Authentication-results: sourceware.org; auth=none
- References: <20131022231556 dot GA5840 at domone dot podge> <20131030151153 dot GA15937 at domone dot podge> <20131105135714 dot GB24734 at domone dot podge>
ping
On Tue, Nov 05, 2013 at 02:57:14PM +0100, OndÅej BÃlka wrote:
> 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.