Re: Compiler warning with 'fast' variable - Mailing list pgsql-hackers

From Bruce Momjian
Subject Re: Compiler warning with 'fast' variable
Date
Msg-id 200904072304.n37N4dH02328@momjian.us
Whole thread Raw
In response to Re: Compiler warning with 'fast' variable  (Tom Lane <tgl@sss.pgh.pa.us>)
Responses Re: Compiler warning with 'fast' variable  (Tom Lane <tgl@sss.pgh.pa.us>)
List pgsql-hackers
Tom Lane wrote:
> Bruce Momjian <bruce@momjian.us> writes:
> > Any idea why I am seeing this warning with the new pg_start_backup()
> > 'fast' flag?
> 
> >     xlog.c:6917: warning: variable `fast' might be clobbered by
> >     `longjmp' or `vfork'
> 
> > The line is in a PG_ENSURE_ERROR_CLEANUP() block.  This is with gcc
> > version 2.95.3.
> 
> That's pretty bizarre --- I don't see it here with gcc 2.95.3,
> and there is no reason for such a warning to appear on a variable
> that isn't changed during the function.
> 
> We could stick a volatile on it but I'd like to find out why this
> particular variable seems to need that.

You ready for this;  changing 'bool' to 'int' supressed the warning:
int     fast = PG_GETARG_BOOL(1);

Using 'char' returns the warning.  Changing the assignment to 'true'
also fixes it:
bool        fast = true;

This also generates no warning about longjmp:
bool        fast = PG_GETARG_TEXT(1);

No warning here either:
bool        fast = (bool) PG_GETARG_DATUM(0);

This generates the warning:
bool        fast = ((bool) ((bool) (PG_GETARG_DATUM(1)) != 0));

This does not:
bool        fast = (bool) (PG_GETARG_DATUM(1) != 0);

--  Bruce Momjian  <bruce@momjian.us>        http://momjian.us EnterpriseDB
http://enterprisedb.com
 + If your life is a hard drive, Christ can be your backup. +


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