Divide by zero error on SPARC/Linux.

Hi All,

In the latest CVS I can get the backend to terminate quite
easily with a divide by 0.

postgres=> select 1/0;
pqReadData() -- backend closed the channel unexpectedly.
This probably means the backend terminated abnormally before or while
processing the request.
We have lost the connection to the backend, so further processing is impossible.
Terminating.
[postgres@sparclinux pgsql]$

A bt on the core shows:-

I don't know if this is recently introduced behaviour or if
it's platform dependant. I can't recall trying this before
so maybe it's always happened on S/Linux.

My immediate thought is to include a check for divide by 0
in the intXXdiv() functions and do something like an elog(WARN,...)

Firstly, what do other people get on their platform?

I get:

ttest=> select 1/0;
ERROR: floating point exception! The last floating point operation
either exceeded legal ranges or was a divide by zero

so it looks like the signal. Check these lines:

#$ gid FloatExceptionHandler
backend/postmaster/postmaster.c:1247: pqsignal(SIGFPE, FloatExceptionHandler);
backend/tcop/postgres.c:772: FloatExceptionHandler(SIGNAL_ARGS)
include/tcop/tcopprot.h:37: extern void FloatExceptionHandler(SIGNAL_ARGS);

-- 
Bruce Momjian                          |  830 Blythe Avenue
maillist@candle.pha.pa.us              |  Drexel Hill, Pennsylvania 19026
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Bruce,

That's what I would have half expected too but am I actually using
any floating point arithmetic?

The function called is int4div() which simply does a, return (arg1/arg2),
so I would have expected integer arithmetic.

If I cast to float I get:-

postgres=> select 1::float8/0::float8;
ERROR: float8div: divide by zero error
postgres=>

The error coming courtesy of :-

if (*arg2 == 0.0)
elog(ERROR, "float8div: divide by zero error");

in backend/utils/adt/float.c:604

I'm still puzzled but lean towards a signal problem too.

I do get FP exceptions as there's one in the float8.out regression
test, where there shouldn't be one!!

QUERY: SELECT '' AS bad, : (f.f1) from FLOAT8_TBL f;
ERROR: floating point exception! The last floating point operation either
exceeded legal ranges or was a divide by zero
QUERY: SELECT '' AS bad, f.f1 / '0.0' from FLOAT8_TBL f;
ERROR: float8div: divide by zero error

Keith.

Bruce Momjian <maillist@candle.pha.pa.us>

Hi All,

In the latest CVS I can get the backend to terminate quite
easily with a divide by 0.

postgres=> select 1/0;
pqReadData() -- backend closed the channel unexpectedly.
This probably means the backend terminated abnormally before or

while

processing the request.
We have lost the connection to the backend, so further processing is

impossible.

Terminating.
[postgres@sparclinux pgsql]$

A bt on the core shows:-

I don't know if this is recently introduced behaviour or if
it's platform dependant. I can't recall trying this before
so maybe it's always happened on S/Linux.

My immediate thought is to include a check for divide by 0
in the intXXdiv() functions and do something like an elog(WARN,...)

Firstly, what do other people get on their platform?

I get:

ttest=> select 1/0;
ERROR: floating point exception! The last floating point operation
either exceeded legal ranges or was a divide by zero

so it looks like the signal. Check these lines:

#$ gid FloatExceptionHandler
backend/postmaster/postmaster.c:1247: pqsignal(SIGFPE,

FloatExceptionHandler);

Bruce,

That's what I would have half expected too but am I actually using
any floating point arithmetic?

The function called is int4div() which simply does a, return (arg1/arg2),
so I would have expected integer arithmetic.

If I cast to float I get:-

postgres=> select 1::float8/0::float8;
ERROR: float8div: divide by zero error
postgres=>

I recommend you put debugs around where it is crashing, and the
reproduce it in a C program, with the same signal() call to catch it,
and see if it works.

-- 
Bruce Momjian                          |  830 Blythe Avenue
maillist@candle.pha.pa.us              |  Drexel Hill, Pennsylvania 19026
  +  If your life is a hard drive,     |  (610) 353-9879(w)
  +  Christ can be your backup.        |  (610) 853-3000(h)