From: Tom Lane <tgl@sss.pgh.pa.us>
To: Peter Eisentraut <peter.eisentraut@2ndquadrant.com>
Cc: Alvaro Herrera <alvherre@2ndquadrant.com>
Cc: pgsql-hackers <pgsql-hackers@postgresql.org>
Subject: Re: GCC 7 warnings
Date: Wed, 12 Apr 2017 11:31:09 -0400
Message-ID: <6997.1492011069@sss.pgh.pa.us> (raw)
In-Reply-To: <600b3625-603a-e400-7881-075830e98ba3@2ndquadrant.com>
References: <20170411175708.coshtfzejgaqhar2@alvherre.pgsql>
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Peter Eisentraut <peter.eisentraut@2ndquadrant.com> writes:
> On 4/12/17 00:12, Tom Lane wrote:
>> Now a human can see that saved_timeval.tv_usec must be 0..999999, so
>> that the %d format item must always emit exactly 3 characters, which
>> means that really 5 bytes would be enough. I wouldn't expect a
>> compiler to know that, but if it's making a generic assumption about
>> the worst-case width of %d, shouldn't it conclude that we might need
>> as many as 13 bytes for the buffer? Why does msbuf[10] satisfy it
>> if msbuf[8] doesn't?
> Because the /1000 takes off three digits?
Huh ... I would not really have expected it to figure that out, but
this makes it pretty clear that it did:
> test.c:11:15: note: directive argument in the range [-2147483, 2147483]
> (This is with -O2. With -O0 it only asks for 5 bytes.)
But that reinforces my suspicion that the intelligence brought to bear
here will be variable. I'd still go for msbuf[16]; it's not like
anybody's going to notice the extra stack consumption.
regards, tom lane
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To: pgsql-hackers@postgresql.org
Cc: tgl@sss.pgh.pa.us, peter.eisentraut@2ndquadrant.com, alvherre@2ndquadrant.com
Subject: Re: GCC 7 warnings
In-Reply-To: <6997.1492011069@sss.pgh.pa.us>
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