new gcc 7.0.1 warnings

Pavel Stehule <pavel.stehule@gmail.com> writes:

float.c:382:5: note: ‘snprintf’ output between 2 and 311 bytes into a
destination of size 65
float.c:618:5: note: ‘snprintf’ output between 2 and 311 bytes into a
destination of size 129

That's kind of annoying. I suppose the point is that the compiler can't
see what precision we're selecting, and with sufficiently large precision
the output could be that wide. But actually the precision should be small
enough to make that OK.

Do the warnings go away if you add some explicit guard to the precision
variable, say like this:

{
int ndig = DBL_DIG + extra_float_digits;

                if (ndig < 1)
                    ndig = 1;
+               if (ndig > 50)
+                   ndig = 50;

snprintf(ascii, MAXDOUBLEWIDTH + 1, "%.*g", ndig, num);
}

If not, I guess we could increase the size of the palloc'd strings,
but that seems wasteful.

regards, tom lane

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2017-02-18 18:35 GMT+01:00 Tom Lane <tgl@sss.pgh.pa.us>:

Pavel Stehule <pavel.stehule@gmail.com> writes:

float.c:382:5: note: ‘snprintf’ output between 2 and 311 bytes into a
destination of size 65
float.c:618:5: note: ‘snprintf’ output between 2 and 311 bytes into a
destination of size 129

That's kind of annoying. I suppose the point is that the compiler can't
see what precision we're selecting, and with sufficiently large precision
the output could be that wide. But actually the precision should be small
enough to make that OK.

Do the warnings go away if you add some explicit guard to the precision
variable, say like this:

{
int ndig = DBL_DIG + extra_float_digits;

if (ndig < 1)
ndig = 1;
+               if (ndig > 50)
+                   ndig = 50;

This fix doesn't help

Regards

Pavel

On 2/18/17 02:08, Pavel Stehule wrote:

I am checking new Fedora 26, where new gcc compiler is used.

float.c: In function ‘float4out’:
float.c:382:41: warning: ‘%.*g’ directive output may be truncated
writing between 1 and 310 bytes into a region of size 65
[-Wformat-truncation=]
snprintf(ascii, MAXFLOATWIDTH + 1, "%.*g", ndig, num);

It appears these warnings no longer happen with a newer gcc-7 snapshot.
I'm using

gcc-7 (Debian 7-20170302-1) 7.0.1 20170302 (experimental) [trunk
revision 245832]

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PostgreSQL Development, 24x7 Support, Remote DBA, Training & Services

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2017-03-08 16:59 GMT+01:00 Peter Eisentraut <
peter.eisentraut@2ndquadrant.com>:

On 2/18/17 02:08, Pavel Stehule wrote:

I am checking new Fedora 26, where new gcc compiler is used.

float.c: In function ‘float4out’:
float.c:382:41: warning: ‘%.*g’ directive output may be truncated
writing between 1 and 310 bytes into a region of size 65
[-Wformat-truncation=]
snprintf(ascii, MAXFLOATWIDTH + 1, "%.*g", ndig, num);

It appears these warnings no longer happen with a newer gcc-7 snapshot.
I'm using

gcc-7 (Debian 7-20170302-1) 7.0.1 20170302 (experimental) [trunk
revision 245832]

gcc (GCC) 7.0.1 20170225 is on Fc still :(

Regards

Pavel

Pavel Stehule wrote:

2017-02-18 18:35 GMT+01:00 Tom Lane <tgl@sss.pgh.pa.us>:

Pavel Stehule <pavel.stehule@gmail.com> writes:

Do the warnings go away if you add some explicit guard to the precision
variable, say like this:

{
int ndig = DBL_DIG + extra_float_digits;

if (ndig < 1)
ndig = 1;
+               if (ndig > 50)
+                   ndig = 50;

This fix doesn't help

Ahh, so this is why you had this change in the xmltable patch once!
Heh. Please be more careful.

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2017-03-08 17:33 GMT+01:00 Alvaro Herrera <alvherre@2ndquadrant.com>:

Pavel Stehule wrote:

2017-02-18 18:35 GMT+01:00 Tom Lane <tgl@sss.pgh.pa.us>:

Pavel Stehule <pavel.stehule@gmail.com> writes:

Do the warnings go away if you add some explicit guard to the precision
variable, say like this:

{
int ndig = DBL_DIG + extra_float_digits;

if (ndig < 1)
ndig = 1;
+               if (ndig > 50)
+                   ndig = 50;

This fix doesn't help

Ahh, so this is why you had this change in the xmltable patch once!
Heh. Please be more careful.

grr :(

I am sorry

Pavel