| From: | Andres Freund <andres(at)anarazel(dot)de> |
|---|---|
| To: | Nathan Bossart <nathandbossart(at)gmail(dot)com> |
| Cc: | Heikki Linnakangas <hlinnaka(at)iki(dot)fi>, Mats Kindahl <mats(at)timescale(dot)com>, Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us>, pgsql-hackers(at)lists(dot)postgresql(dot)org |
| Subject: | Re: glibc qsort() vulnerability |
| Date: | 2024-02-08 02:06:37 |
| Message-ID: | 20240208020637.3irwi5vph4fbxw2f@awork3.anarazel.de |
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| Lists: | pgsql-hackers |
Hi,
On 2024-02-07 19:52:11 -0600, Nathan Bossart wrote:
> On Wed, Feb 07, 2024 at 04:42:07PM -0800, Andres Freund wrote:
> > On 2024-02-07 16:21:24 -0600, Nathan Bossart wrote:
> >> The assembly for that looks encouraging, but I still need to actually test
> >> it...
> >
> > Possible. For 16bit upcasting to 32bit is clearly the best way. For 32 bit
> > that doesn't work, given the 32bit return, so we need something more.
>
> For the same compASC() test, I see an ~8.4% improvement with your int64
> code
Just to be clear, that code unfortuntely isn't correct, the return value is a
32 bit integer, so the 64bit difference doesn't help. In contrast to the 16bit
case.
> and a ~3.4% improvement with this:
I guess that's still something.
Another branchless variant is (a > b) - (a < b). It seems to get a similar
improvement as the overflow-checking version.
Greetings,
Andres Freund
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