From: | PG Bug reporting form <noreply(at)postgresql(dot)org> |
---|---|
To: | pgsql-bugs(at)lists(dot)postgresql(dot)org |
Cc: | ssubhrajyoti(at)google(dot)com |
Subject: | BUG #17167: UndefinedBehaviorSanitizer: invalid-shift-exponent while running int4shr/int4shl |
Date: | 2021-08-30 09:02:36 |
Message-ID: | 17167-028026e4ca333817@postgresql.org |
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Lists: | pgsql-bugs |
The following bug has been logged on the website:
Bug reference: 17167
Logged by: Subhrajyoti Senapati
Email address: ssubhrajyoti(at)google(dot)com
PostgreSQL version: 12.8
Operating system: Linux
Description:
Hi,
When executing in an asan instrumented build,
```
postgres=> SELECT int4shr(10, -1);
```
throws an error `runtime error: shift exponent 32 is too large for 32-bit
type 'int32' (aka 'int')`
This seems to be coming from this line:
https://github.com/postgres/postgres/blob/c30f54ad732ca5c8762bb68bbe0f51de9137dd72/src/backend/utils/adt/int.c#L1413
While browsing, i found this link:
https://wiki.sei.cmu.edu/confluence/display/c/INT34-C.+Do+not+shift+an+expression+by+a+negative+number+of+bits+or+by+greater+than+or+equal+to+the+number+of+bits+that+exist+in+the+operand,
according to which shifting by negative number of bits or >= bits in the
operand is classified as a undefined behaviour.
Few experiments i tried:
```
postgres=> SELECT int4shr(10, 1);
int4shr
---------
5
(1 row)
postgres=> SELECT int4shr(10, -1);
int4shr
---------
0
(1 row)
postgres=> SELECT int4shr(10, -2);
int4shr
---------
0
(1 row)
```
I am not sure if it's a bug or expected behaviour.
Thanks,
Subhrajyoti
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Next Message | Alexander Lakhin | 2021-08-30 12:00:51 | Re: BUG #17167: UndefinedBehaviorSanitizer: invalid-shift-exponent while running int4shr/int4shl |
Previous Message | David G. Johnston | 2021-08-29 18:44:39 | BUG #17166: PREPARE without types inconsistent type resolving |