| From: | Andres Freund <andres(at)anarazel(dot)de> |
|---|---|
| To: | Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us> |
| Cc: | Michael Banck <michael(dot)banck(at)credativ(dot)de>, Magnus Hagander <magnus(at)hagander(dot)net>, Fabien COELHO <coelho(at)cri(dot)ensmp(dot)fr>, pgsql-hackers <pgsql-hackers(at)postgresql(dot)org> |
| Subject: | Re: pg_verify_checksums and -fno-strict-aliasing |
| Date: | 2018-08-30 21:46:06 |
| Message-ID: | 20180830214606.xpm4bho5nmhfuzlx@alap3.anarazel.de |
| Views: | Whole Thread | Raw Message | Download mbox | Resend email |
| Thread: | |
| Lists: | pgsql-hackers |
Hi,
On 2018-08-30 17:19:28 -0400, Tom Lane wrote:
> So, I've been fooling around trying to get it to work without
> -fno-strict-aliasing, but with little luck so far.
The problem presumably is that pg_checksum_block() accesses the relevant
fields as an uint32, whereas pg_checksum_page() accesses it as a
PageHeader. That's an aliasing violation. *One* cast from char* to
either type is fine, it's accessing under both those types that's
problematic.
One way to fix it would be to memcpy in/out the modified PageHeader, or
just do offset math and memcpy to that offset.
Greetings,
Andres Freund
| From | Date | Subject | |
|---|---|---|---|
| Next Message | Tom Lane | 2018-08-30 21:49:04 | Re: pg_verify_checksums and -fno-strict-aliasing |
| Previous Message | Thomas Munro | 2018-08-30 21:40:59 | Re: B-tree cache prefetches |