From: Tom Lane <tgl@sss.pgh.pa.us>
To: Amit Kapila <amit.kapila16@gmail.com>
Cc: PostgreSQL Hackers <pgsql-hackers@lists.postgresql.org>
Cc: hlinnaka <hlinnaka@iki.fi>
Subject: Re: SerializeParamList vs machines with strict alignment
Date: Mon, 01 Oct 2018 16:49:07 -0400
Message-ID: <28627.1538426947@sss.pgh.pa.us> (raw)
In-Reply-To: <27748.1538425312@sss.pgh.pa.us>
References: <11629.1536550032@sss.pgh.pa.us>
<CAA4eK1JfEc=cqiUiRvUcHYCf=PVEwM_bZ_QiOMHpqGpUMdY8gA@mail.gmail.com>
<8352.1536586500@sss.pgh.pa.us>
<CAA4eK1KTsNC--yPBatOiLJriBfGNgb_vmTF40JcEeZPedcL9YA@mail.gmail.com>
<CAA4eK1KjGVrbMxaoE=tr1uR7mfpVLYui60tO4ANkQQAV+c+Y_A@mail.gmail.com>
<27748.1538425312@sss.pgh.pa.us>
I wrote:
> The attached revised patch contains a test case that demonstrably triggers
> the problem on gaur's host. Oddly, I do not get a crash either on a PPC
> Mac or a Raspberry Pi 3 running Raspbian. I'm not very sure why; I traced
> through things with gdb and it's definitely calling EA_flatten_into with
> an odd address and a non-flattened input. I guess both of those platforms
> have kernel handlers for misaligned accesses? But the Raspbian box ought
> to be nearly the same as chipmunk, which is where we saw the problem to
> begin with, so I'm a bit confused.
Ah: a bit of googling later, the mystery is solved. PPC does have support
for unaligned 32-bit accesses, which is as much as EA_flatten_into needs.
(It's 64-bit operations where you might have a problem.) My info was
also out of date about ARM: more recent processors, at least, can also
do unaligned 32-bit accesses. chipmunk either has a pretty old processor
or it is configured to disable unaligned access.
Apparently the only somewhat-modern architecture that is resolutely
unaligned-unfriendly is MIPS.
regards, tom lane
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To: pgsql-hackers@postgresql.org
Cc: tgl@sss.pgh.pa.us, amit.kapila16@gmail.com, pgsql-hackers@lists.postgresql.org, hlinnaka@iki.fi
Subject: Re: SerializeParamList vs machines with strict alignment
In-Reply-To: <28627.1538426947@sss.pgh.pa.us>
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