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* BUG #17167: UndefinedBehaviorSanitizer: invalid-shift-exponent while running int4shr/int4shl
@ 2021-08-30 09:02 PG Bug reporting form <noreply@postgresql.org>
0 siblings, 1 reply; 2+ messages in thread
From: PG Bug reporting form @ 2021-08-30 09:02 UTC (permalink / raw)
To: pgsql-bugs@lists.postgresql.org; +Cc: ssubhrajyoti@google.com
The following bug has been logged on the website:
Bug reference: 17167
Logged by: Subhrajyoti Senapati
Email address: ssubhrajyoti@google.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...
While browsing, i found this link:
https://wiki.sei.cmu.edu/confluence/display/c/INT34-C.+Do+not+shift+an+expression+by+a+negative+numb...,
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
^ permalink raw reply [nested|flat] 2+ messages in thread
* Re: BUG #17167: UndefinedBehaviorSanitizer: invalid-shift-exponent while running int4shr/int4shl
@ 2021-08-30 12:00 Alexander Lakhin <exclusion@gmail.com>
parent: PG Bug reporting form <noreply@postgresql.org>
0 siblings, 0 replies; 2+ messages in thread
From: Alexander Lakhin @ 2021-08-30 12:00 UTC (permalink / raw)
To: ssubhrajyoti@google.com, pgsql-bugs@lists.postgresql.org, PG Bug reporting form <noreply@postgresql.org>
Hello Subhrajyoti,
30.08.2021 12:02, PG Bug reporting form wrote:
> Bug reference: 17167
>
> 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 like a duplicate of #16790:
https://www.postgresql.org/message-id/flat/16790-c2a81c92a8776c5b%40postgresql.org
Best regards,
Alexander
^ permalink raw reply [nested|flat] 2+ messages in thread
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