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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 9bcd12d223a8990254b65e2dada54faa5d2742f3 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>