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Avoid -Wstringop-overflow= warning in iconv module.

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On s390x when compiling with GCC 12, I get this warning:
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];
      |                 ^~~~~~~

This patch tells the compiler that inend is always behind inptr which
avoids the warning.  Note that the SINGLE function is only used to
implement the mb*towc*() or wc*tomb*() functions.  Those functions use
inptr and inend pointing to a variable on stack, compute the inend pointer
or explicitly check the arguments which always leads to inptr < inend.

Special notes for backporters (according to Siddhesh Poyarekar):
If someone wants to backport this patch to release branches, they should
also backport the following wcrtomb change. Otherwise the assumptions
assumed by this patch are not true.

commit 9bcd12d223
Author: Siddhesh Poyarekar <siddhesh@sourceware.org>
Date:   Fri May 13 19:10:15 2022 +0530

    wcrtomb: Make behavior POSIX compliant

Reviewed-by: Siddhesh Poyarekar <siddhesh@sourceware.org>
This commit is contained in:
Stefan Liebler 2022-06-03 14:52:51 +02:00
parent fdaf78656f
commit 876cdf517d
1 changed files with 8 additions and 2 deletions
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10
iconv/loop.c
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@ -435,11 +435,17 @@ SINGLE(LOOPFCT) (struct __gconv_step *step,
return __GCONV_FULL_OUTPUT;
/* Now add characters from the normal input buffer. */
if (inlen >= MAX_NEEDED_INPUT)
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. */
being too large after a previous conversion step.
Starting with GCC 12, we also have mark the inptr >= inend
case as unreachable to omit the warning. Note that this SINGLE
function is only used to implement the mb*towc*() or wc*tomb*()
functions. Those functions use inptr and inend pointing to a
variable on stack, compute the inend pointer or explicitly check
the arguments which always leads to inptr < inend. */
__builtin_unreachable ();
do
bytebuf[inlen++] = *inptr++;