pgsql: Disable -faggressive-loop-optimizations in gcc 4.8+ for pre-9.2

Tom Lane wrote:

Disable -faggressive-loop-optimizations in gcc 4.8+ for pre-9.2 branches.

With this optimization flag enabled, recent versions of gcc can generate
incorrect code that assumes variable-length arrays (such as oidvector)
are actually fixed-length because they're embedded in some larger struct.
The known instance of this problem was fixed in 9.2 and up by commit
8137f2c32322c624e0431fac1621e8e9315202f9 and followon work, which hides
actually-variable-length catalog fields from the compiler altogether.
And we plan to gradually convert variable-length fields to official
"flexible array member" notation over time, which should prevent this type
of bug from reappearing as gcc gets smarter. We're not going to try to
back-port those changes into older branches, though, so apply this
band-aid instead.

Would anybody object to me pushing this commit to branches 8.2 and 8.3?

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On Tue, Jan 20, 2015 at 10:30 AM, Alvaro Herrera
<alvherre@2ndquadrant.com> wrote:

Tom Lane wrote:

Disable -faggressive-loop-optimizations in gcc 4.8+ for pre-9.2 branches.
With this optimization flag enabled, recent versions of gcc can generate
incorrect code that assumes variable-length arrays (such as oidvector)
are actually fixed-length because they're embedded in some larger struct.
The known instance of this problem was fixed in 9.2 and up by commit
8137f2c32322c624e0431fac1621e8e9315202f9 and followon work, which hides
actually-variable-length catalog fields from the compiler altogether.
And we plan to gradually convert variable-length fields to official
"flexible array member" notation over time, which should prevent this type
of bug from reappearing as gcc gets smarter. We're not going to try to
back-port those changes into older branches, though, so apply this
band-aid instead.

Would anybody object to me pushing this commit to branches 8.2 and 8.3?

Since those branches are out of support, I am not sure what the point
is. If we want people to be able to use those branches reasonably we
need to back-port fixes for critical security and stability issues,
not just this one thing.

But maybe I am missing something.

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Robert Haas
EnterpriseDB: http://www.enterprisedb.com
The Enterprise PostgreSQL Company

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On 2015-01-20 11:10:53 -0500, Robert Haas wrote:

On Tue, Jan 20, 2015 at 10:30 AM, Alvaro Herrera
<alvherre@2ndquadrant.com> wrote:

Tom Lane wrote:

Disable -faggressive-loop-optimizations in gcc 4.8+ for pre-9.2 branches.
With this optimization flag enabled, recent versions of gcc can generate
incorrect code that assumes variable-length arrays (such as oidvector)
are actually fixed-length because they're embedded in some larger struct.
The known instance of this problem was fixed in 9.2 and up by commit
8137f2c32322c624e0431fac1621e8e9315202f9 and followon work, which hides
actually-variable-length catalog fields from the compiler altogether.
And we plan to gradually convert variable-length fields to official
"flexible array member" notation over time, which should prevent this type
of bug from reappearing as gcc gets smarter. We're not going to try to
back-port those changes into older branches, though, so apply this
band-aid instead.

Would anybody object to me pushing this commit to branches 8.2 and 8.3?

Since those branches are out of support, I am not sure what the point
is. If we want people to be able to use those branches reasonably we
need to back-port fixes for critical security and stability issues,
not just this one thing.

But maybe I am missing something.

Supporting and being able to compile and run 'make check' (which doesn't
complete >= gcc 4.8) aren't the same thing though. And we e.g. try to
provide pg_dump and libpq support for older versions, which is hard to
ensure if you can't run them.

I personally think that being able to at least compile/make check old
versions a bit longer is a good idea.

Greetings,

Andres Freund

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Robert Haas wrote:

Would anybody object to me pushing this commit to branches 8.2 and 8.3?

Since those branches are out of support, I am not sure what the point
is. If we want people to be able to use those branches reasonably we
need to back-port fixes for critical security and stability issues,
not just this one thing.

But maybe I am missing something.

I just want to make it easy to compile those branches with current
toolset so that I can study their behavior to suggest workarounds for
customer problems etc -- nothing more. I am not proposing to open them
up again for support. Of course, I can carry the patched branches
locally if there is strong opposition, but since it's harmless, I don't
see why would there be any such. Another easy workaround is to add -O0
to CFLAGS, and I can script that easily too.

Without this patch or -O0, initdb fails with

inicializando pg_authid ... FATAL: wrong number of index expressions
SENTENCIA: CREATE TRIGGER pg_sync_pg_database AFTER INSERT OR UPDATE OR DELETE ON pg_database FOR EACH STATEMENT EXECUTE PROCEDURE flatfile_update_trigger();

There is the additional problem that contrib/cube fails to compile, but
I don't care enough about that one:

/pgsql/source/REL8_3_STABLE/contrib/cube/cubeparse.y:61:17: error: ‘result’ undeclared (first use in this function)
*((void **)result) = write_box( dim, $2, $4 );
^

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On Tue, Jan 20, 2015 at 11:18 AM, Alvaro Herrera
<alvherre@2ndquadrant.com> wrote:

Robert Haas wrote:

Would anybody object to me pushing this commit to branches 8.2 and 8.3?

Since those branches are out of support, I am not sure what the point
is. If we want people to be able to use those branches reasonably we
need to back-port fixes for critical security and stability issues,
not just this one thing.

But maybe I am missing something.

I just want to make it easy to compile those branches with current
toolset so that I can study their behavior to suggest workarounds for
customer problems etc -- nothing more. I am not proposing to open them
up again for support.

Oh, I see. Well, that doesn't bother me, then.

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Robert Haas
EnterpriseDB: http://www.enterprisedb.com
The Enterprise PostgreSQL Company

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--On 20. Januar 2015 17:15:01 +0100 Andres Freund <andres@2ndquadrant.com>
wrote:

I personally think that being able to at least compile/make check old
versions a bit longer is a good idea.

+1 from me for this idea.

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Thanks

Bernd

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Bernd Helmle wrote:

--On 20. Januar 2015 17:15:01 +0100 Andres Freund <andres@2ndquadrant.com>
wrote:

I personally think that being able to at least compile/make check old
versions a bit longer is a good idea.

+1 from me for this idea.

Already done yesterday :-)

Thanks,

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PostgreSQL Development, 24x7 Support, Remote DBA, Training & Services

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