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Re: [PATCH] libdw: Add get_uleb128 and get_sleb128 bounds checking.
- From: Josh Stone <jistone at redhat dot com>
- To: elfutils-devel at lists dot fedorahosted dot org
- Date: Mon, 15 Dec 2014 11:34:02 -0800
- Subject: Re: [PATCH] libdw: Add get_uleb128 and get_sleb128 bounds checking.
On 12/14/2014 02:18 PM, Mark Wielaard wrote:
> This finally adds bounds checking to get_[us]leb128 (with two exceptions,
> see below). The performance results are a little puzzling, so I hope
> Josh can take a look how things are for him.
> On one system, with 3.10.0-123.13.1.el7.x86_64, varlocs -k slows down:
> 0.160: 53.65
> master: 52.24
> mjw/pending: 56.35
> But on another, with 3.17.4-301.fc21.x86_64, varlocs -k speeds up:
> 0.160: 69.41
> master: 69.03
> mjw/pending: 68.29
> Output is the same between versions for each system.
These are probably different compilers too, right? So I suspect the
newer compiler just noticed an optimization opportunity.
AFAICT, the change to __libdw_form_val_len's parameters, pending commit
1a069eb7ae22, makes the bulk of the difference. But it does seem to be
a bit faster still in the leb128 commit 4f6de27c6043 -- curious!