Bug#977279: ploop FTBFS on armhf, i386: error: ‘%s’ directive output may be truncated writing between 2 and 2147483645 bytes into a region of size 4083

[Helmut Grohne <helmut@subdivi.de>]

Source: ploop
Version: 1.15-9
Severity: serious
Tags: ftbfs

ploop fails to build from source on armhf and i386 (presumably 32bit
architectures in general):

reproducible builds i386:
https://tests.reproducible-builds.org/debian/rbuild/unstable/i386/ploop_1.15-9.rbuild.log.gz
| delta_sysfs.c: In function 'dev_num2dev_start':
| delta_sysfs.c:304:51: error: '%s' directive output may be truncated writing between 2 and 2147483645 bytes into a region of size 4083 [-Werror=format-truncation=]
|   304 |   snprintf(nbuf, sizeof(nbuf) - 1, "/sys/block/%s/%s",
|       |                                                   ^~
| In file included from /usr/include/stdio.h:867,
|                  from delta_sysfs.c:19:
| /usr/include/i386-linux-gnu/bits/stdio2.h:67:10: note: '__builtin___snprintf_chk' output 15 or more bytes (assuming 2147483658) into a destination of size 4095
|    67 |   return __builtin___snprintf_chk (__s, __n, __USE_FORTIFY_LEVEL - 1,
|       |          ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
|    68 |        __bos (__s), __fmt, __va_arg_pack ());
|       |        ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
| cc1: all warnings being treated as errors

reproducible builds armhf:
https://tests.reproducible-builds.org/debian/rbuild/unstable/armhf/ploop_1.15-9.rbuild.log.gz

crossqa armhf:
http://crossqa.debian.net/build/ploop_1.15-9_armhf_20201011140323.log

A local cross build for armel has exactly the same symptom.

Helmut