* Question regarding gcc 12 Werror=stringop-overflow in iconv/loop.c
@ 2022-04-27 14:55 Stefan Liebler
2022-04-27 15:24 ` Florian Weimer
0 siblings, 1 reply; 2+ messages in thread
From: Stefan Liebler @ 2022-04-27 14:55 UTC (permalink / raw)
To: GNU C Library
Hi,
with GCC 12, when building with -O3 I'm getting this werror on s390x
when compiling sysdeps/s390/utf8-utf16-z9.c:
../iconv/loop.c: In function ‘__from_utf8_loop_etf3eh_single’:
../iconv/loop.c:445:22: error: writing 1 byte into a region of size 0
[-Werror=stringop-overflow=]
445 | bytebuf[inlen++] = *inptr++;
| ~~~~~~~~~~~~~~~~~^~~~~~~~~~
../iconv/loop.c:381:17: note: at offset 4 into destination object
‘bytebuf’ of size 4
381 | unsigned char bytebuf[MAX_NEEDED_INPUT];
| ^~~~~~~
../iconv/loop.c:445:22: error: writing 1 byte into a region of size 0
[-Werror=stringop-overflow=]
445 | bytebuf[inlen++] = *inptr++;
| ~~~~~~~~~~~~~~~~~^~~~~~~~~~
../iconv/loop.c:381:17: note: at offset 5 into destination object
‘bytebuf’ of size 4
381 | unsigned char bytebuf[MAX_NEEDED_INPUT];
| ^~~~~~~
In this case MAX_NEEDED_INPUT is 4.
I can silence the warning if I use a while-loop in loop.c:
while (inlen < MAX_NEEDED_INPUT && inptr < inend)
bytebuf[inlen++] = *inptr++;
instead of the do-while-loop.
But then I'm get an werror with GCC 11.2 in iconvdata/gbgbk.c.
Is there a guarantee that (inptr < inend) is always met?
Then extending the unreachable-case above the loop would silence the
werrors in both files:
if (inlen >= MAX_NEEDED_INPUT || inptr >= inend)
/* Avoid a -Wstringop-overflow= warning when this loop is
unrolled. The compiler cannot otherwise see that this is
unreachable because it depends on (state->__count & 7) not
being too large after a previous conversion step. */
__builtin_unreachable ();
Otherwise an extra check above the loop like this, would also silence
the werrors in both files:
if (inptr >= inend)
return __GCONV_INCOMPLETE_INPUT;
Thanks in advance for any help and hints.
Stefan
^ permalink raw reply [flat|nested] 2+ messages in thread
* Re: Question regarding gcc 12 Werror=stringop-overflow in iconv/loop.c
2022-04-27 14:55 Question regarding gcc 12 Werror=stringop-overflow in iconv/loop.c Stefan Liebler
@ 2022-04-27 15:24 ` Florian Weimer
0 siblings, 0 replies; 2+ messages in thread
From: Florian Weimer @ 2022-04-27 15:24 UTC (permalink / raw)
To: Stefan Liebler via Libc-alpha; +Cc: Stefan Liebler
* Stefan Liebler via Libc-alpha:
> Is there a guarantee that (inptr < inend) is always met?
When calling iconv (the external API), inptr <= inend must hold (no
pointer wraparound). I think there is a minimum-input-size check in
iconv/loop.c, so it follows that we have inptr < inend. I think.
Thanks,
Florian
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