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Tom Lane 0e87dfe464 Harden memory context allocators against bogus chunk pointers. 
Before commit c6e0fe1f2, functions such as AllocSetFree could pretty
safely presume that they were given a valid chunk pointer for their
own type of context, because the indirect call through a memory
context object and method struct would be very unlikely to work
otherwise.  But now, if pfree() is mistakenly invoked on a pointer
to garbage, we have three chances in eight of ending up at one of
these functions.  That means we need to take extra measures to
verify that we are looking at what we're supposed to be looking at,
especially in debug builds.

Hence, add code to verify that the chunk's back-link to a block header
leads to a memory context object that satisfies the right sort of
IsA() check.  This is still a bit weaker than what we did before,
but for the moment assume that an IsA() check is sufficient.

As a compromise between speed and safety, implement these checks
as Asserts when dealing with small chunks but plain test-and-elogs
when dealing with large (external) chunks.  The latter case should
not be too performance-critical, but the former case probably is.
In slab.c, all chunks are small; but nonetheless use a plain test
in SlabRealloc, because that is certainly not performance-critical,
indeed we should be suspicious that it's being called in error.

In aset.c, additionally add some assertions that the "value" field
of the chunk header is within the small range allowed for freelist
indexes.  Without that, we might find ourselves trying to wipe
most of memory when CLOBBER_FREED_MEMORY is enabled, or scribbling
on a "freelist header" that's far away from the context object.

Eventually, field experience might show us that it's smarter for
these tests to be active always, but for now we'll try to get
away with just having them as assertions.

While at it, also be more uniform about asserting that context
objects passed as parameters are of the type we expect.  Some
places missed that altogether, and slab.c was for no very good
reason doing it differently from the other allocators.

Discussion: https://postgr.es/m/3578387.1665244345@sss.pgh.pa.us
 		2022-10-10 18:45:34 -04:00
config meson: Add initial version of meson based build system 2022-09-21 22:37:17 -07:00
contrib Simplify our Assert infrastructure a little. 2022-10-10 15:16:56 -04:00
doc doc: clarify description for log_startup_progress_interval 2022-10-05 15:53:40 -04:00
src Harden memory context allocators against bogus chunk pointers. 2022-10-10 18:45:34 -04:00
.cirrus.yml meson: Add support for building with precompiled headers 2022-10-06 17:19:30 -07:00
.dir-locals.el Make Emacs perl-mode indent more like perltidy. 2019-01-13 11:32:31 -08:00
.editorconfig Add .editorconfig 2019-12-18 09:13:13 +01:00
.git-blame-ignore-revs Add b2e6e7682 to .git-blame-ignore-revs 2022-09-08 14:06:59 +07:00
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.gitignore Support for optimizing and emitting code in LLVM JIT provider. 2018-03-22 11:05:22 -07:00
COPYRIGHT Update copyright for 2022 2022-01-07 19:04:57 -05:00
GNUmakefile.in Run tests of libpq on installcheck-world, checkprep and check-world 2022-06-03 13:15:20 +09:00
HISTORY Canonicalize some URLs 2020-02-10 20:47:50 +01:00
Makefile Dynamically find correct installation docs in Makefile. 2022-01-19 14:48:25 +01:00
README Canonicalize some URLs 2020-02-10 20:47:50 +01:00
README.git Canonicalize some URLs 2020-02-10 20:47:50 +01:00
aclocal.m4 Probe $PROVE not $PERL while checking for modules needed by TAP tests. 2021-11-22 12:54:52 -05:00
configure autoconf: Rely on ar supporting index creation 2022-10-07 11:53:39 -07:00
configure.ac autoconf: Rely on ar supporting index creation 2022-10-07 11:53:39 -07:00
meson.build Add -Wshadow=compatible-local to the standard compilation flags 2022-10-07 16:50:31 +13:00
meson_options.txt meson: Add initial version of meson based build system 2022-09-21 22:37:17 -07:00

README 

PostgreSQL Database Management System
=====================================

This directory contains the source code distribution of the PostgreSQL
database management system.

PostgreSQL is an advanced object-relational database management system
that supports an extended subset of the SQL standard, including
transactions, foreign keys, subqueries, triggers, user-defined types
and functions.  This distribution also contains C language bindings.

PostgreSQL has many language interfaces, many of which are listed here:

	https://www.postgresql.org/download/

See the file INSTALL for instructions on how to build and install
PostgreSQL.  That file also lists supported operating systems and
hardware platforms and contains information regarding any other
software packages that are required to build or run the PostgreSQL
system.  Copyright and license information can be found in the
file COPYRIGHT.  A comprehensive documentation set is included in this
distribution; it can be read as described in the installation
instructions.

The latest version of this software may be obtained at
https://www.postgresql.org/download/.  For more information look at our
web site located at https://www.postgresql.org/.