Fix use of possible uninitialized variable retval (src/pl/plpgsql/src/pl_handler.c)

At Mon, 27 May 2024 11:31:24 -0300, Ranier Vilela <ranier.vf@gmail.com> wrote in

Hi.

The function *plpgsql_inline_handler* can use uninitialized
variable retval, if PG_TRY fails.
Fix like function*plpgsql_call_handler* wich declare retval as
volatile and initialize to (Datum 0).

If PG_TRY fails, retval is not actually accessed, so no real issue
exists. Commit 7292fd8f1c changed plpgsql_call_handler() to the
current form, but as stated in its commit message, it did not fix a
real issue and was solely to silence compiler.

I believe we do not need to modify plpgsql_inline_handler() unless
compiler actually issues a false warning for it.

regards.

--
Kyotaro Horiguchi
NTT Open Source Software Center

On Wed, Jun 05, 2024 at 01:12:41PM +0900, Kyotaro Horiguchi wrote:

At Mon, 27 May 2024 11:31:24 -0300, Ranier Vilela <ranier.vf@gmail.com> wrote in

The function *plpgsql_inline_handler* can use uninitialized
variable retval, if PG_TRY fails.
Fix like function*plpgsql_call_handler* wich declare retval as
volatile and initialize to (Datum 0).

You forgot to read elog.h, explaining under which circumstances
variables related to TRY/CATCH block should be marked as volatile.
There is a big "Note:" paragraph.

It is not the first time that this is mentioned on this list: but
sending a report without looking at the reason why a change is
justified makes everybody waste time. That's not productive.

If PG_TRY fails, retval is not actually accessed, so no real issue
exists. Commit 7292fd8f1c changed plpgsql_call_handler() to the
current form, but as stated in its commit message, it did not fix a
real issue and was solely to silence compiler.

This complain was from lapwing, that uses a version of gcc which
produces a lot of noise with incorrect issues. It is one of the only
32b buildfarm members, so it still has a lot of value.

I believe we do not need to modify plpgsql_inline_handler() unless
compiler actually issues a false warning for it.

If we were to do something, that would be to remove the volatile from
plpgsql_call_handler() at the end once we don't have in the buildfarm
compilers that complain about it, because there is no reason to use a
volatile in this case. :)
--
Michael

Em qua., 5 de jun. de 2024 às 01:12, Kyotaro Horiguchi <
horikyota.ntt@gmail.com> escreveu:

At Mon, 27 May 2024 11:31:24 -0300, Ranier Vilela <ranier.vf@gmail.com>
wrote in

Hi.

The function *plpgsql_inline_handler* can use uninitialized
variable retval, if PG_TRY fails.
Fix like function*plpgsql_call_handler* wich declare retval as
volatile and initialize to (Datum 0).

If PG_TRY fails, retval is not actually accessed, so no real issue
exists.

You say it for this call
PG_RE_THROW();

Commit 7292fd8f1c changed plpgsql_call_handler() to the
current form, but as stated in its commit message, it did not fix a
real issue and was solely to silence compiler.

I believe we do not need to modify plpgsql_inline_handler() unless
compiler actually issues a false warning for it.

Yeah, there is a warning, but not from the compiler.

best regards,
Ranier Vilela

Em qua., 5 de jun. de 2024 às 02:04, Michael Paquier <michael@paquier.xyz>
escreveu:

On Wed, Jun 05, 2024 at 01:12:41PM +0900, Kyotaro Horiguchi wrote:

At Mon, 27 May 2024 11:31:24 -0300, Ranier Vilela <ranier.vf@gmail.com>

wrote in

The function *plpgsql_inline_handler* can use uninitialized
variable retval, if PG_TRY fails.
Fix like function*plpgsql_call_handler* wich declare retval as
volatile and initialize to (Datum 0).

You forgot to read elog.h, explaining under which circumstances
variables related to TRY/CATCH block should be marked as volatile.
There is a big "Note:" paragraph.

It is not the first time that this is mentioned on this list: but
sending a report without looking at the reason why a change is
justified makes everybody waste time. That's not productive.

Of course, this is very bad when it happens.

If PG_TRY fails, retval is not actually accessed, so no real issue
exists. Commit 7292fd8f1c changed plpgsql_call_handler() to the
current form, but as stated in its commit message, it did not fix a
real issue and was solely to silence compiler.

This complain was from lapwing, that uses a version of gcc which
produces a lot of noise with incorrect issues. It is one of the only
32b buildfarm members, so it still has a lot of value.

I posted the report, because of an uninitialized variable warning.
Which is one of the most problematic situations, when it *actually exists*.

I believe we do not need to modify plpgsql_inline_handler() unless
compiler actually issues a false warning for it.

If we were to do something, that would be to remove the volatile from
plpgsql_call_handler() at the end once we don't have in the buildfarm
compilers that complain about it, because there is no reason to use a
volatile in this case. :)

I don't see any motivation, since there are no reports.

best regards,
Ranier Vilela

On Wed, Jun 5, 2024 at 1:05 PM Michael Paquier <michael@paquier.xyz> wrote:

This complain was from lapwing, that uses a version of gcc which
produces a lot of noise with incorrect issues. It is one of the only
32b buildfarm members, so it still has a lot of value.

Note that I removed the -Werror from lapwing a long time ago, so at
least this animal shouldn't lead to hackish fixes for false positive
anymore.

On Wed, Jun 05, 2024 at 10:27:51PM +0800, Julien Rouhaud wrote:

Note that I removed the -Werror from lapwing a long time ago, so at
least this animal shouldn't lead to hackish fixes for false positive
anymore.

That's good to know. Thanks for the update.
--
Michael