| From: | Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us> |
|---|---|
| To: | Mark Dilger <mark(dot)dilger(at)enterprisedb(dot)com> |
| Cc: | Robert Haas <robertmhaas(at)gmail(dot)com>, Peter Geoghegan <pg(at)bowt(dot)ie>, "Andrey M(dot) Borodin" <x4mmm(at)yandex-team(dot)ru>, Stephen Frost <sfrost(at)snowman(dot)net>, Michael Paquier <michael(at)paquier(dot)xyz>, Amul Sul <sulamul(at)gmail(dot)com>, Dilip Kumar <dilipbalaut(at)gmail(dot)com>, Andres Freund <andres(at)anarazel(dot)de>, PostgreSQL-development <pgsql-hackers(at)postgresql(dot)org> |
| Subject: | Re: new heapcheck contrib module |
| Date: | 2020-10-22 21:06:19 |
| Message-ID: | 43209.1603400779@sss.pgh.pa.us |
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| Lists: | pgsql-hackers |
I wrote:
> Mark Dilger <mark(dot)dilger(at)enterprisedb(dot)com> writes:
>> It is seeking to position 32 and writing '\x77\x77\x77\x77'. x86_64 is
>> little-endian, and ppc32 and sparc64 are both big-endian, right?
> They are, but that should not meaningfully affect the results of
> that corruption step. You zapped only one line pointer not
> several, but it would look the same regardless of endiannness.
Oh, wait a second. ItemIdData has the flag bits in the middle:
typedef struct ItemIdData
{
unsigned lp_off:15, /* offset to tuple (from start of page) */
lp_flags:2, /* state of line pointer, see below */
lp_len:15; /* byte length of tuple */
} ItemIdData;
meaning that for that particular bit pattern, one endianness
is going to see the flags as 01 (LP_NORMAL) and the other as 10
(LP_REDIRECT). The offset/len are corrupt either way, but
I'd certainly expect that amcheck would produce different
complaints about those two cases. So it's unsurprising if
this test case's output is endian-dependent.
regards, tom lane
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