make—can I suppress a format-truncation error?

I'm trying to install intel's psm package from source. When I run make, I get this weird error.

psm

make

$ make
...
make libpsm_infinipath.so
make[1]: Entering directory `/home/kilojoules/psm'
cc -Wall -Werror -fpic -fPIC -D_GNU_SOURCE -funwind-tables -O3 -g3 -DNVALGRIND -I. -I/home/kilojoules/psm/include -I/home/kilojoules/psm/mpspawn -I/home/kilojoules/psm/include/linux-x86_64 -c psm_context.c -o psm_context.o
cc -Wall -Werror -fpic -fPIC -D_GNU_SOURCE -funwind-tables -O3 -g3 -DNVALGRIND -I. -I/home/kilojoules/psm/include -I/home/kilojoules/psm/mpspawn -I/home/kilojoules/psm/include/linux-x86_64 -c psm_ep.c -o psm_ep.o
psm_ep.c: In function '__psm_ep_open':
psm_ep.c:1013:27: error: '%1d' directive output may be truncated writing between 1 and 5 bytes into a region of size 4 [-Werror=format-truncation=]
snprintf(pvalue, 4, "%1d", ports[0]);
^~~
psm_ep.c:1013:26: note: directive argument in the range [0, 65535]
snprintf(pvalue, 4, "%1d", ports[0]);
^~~~~
psm_ep.c:1013:6: note: 'snprintf' output between 2 and 6 bytes into a destination of size 4
snprintf(pvalue, 4, "%1d", ports[0]);
^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
psm_ep.c:1041:27: error: '%1d' directive output may be truncated writing between 1 and 5 bytes into a region of size 4 [-Werror=format-truncation=]
snprintf(pvalue, 4, "%1d", ports[i]);
^~~
psm_ep.c:1041:26: note: directive argument in the range [0, 65535]
snprintf(pvalue, 4, "%1d", ports[i]);
^~~~~
psm_ep.c:1041:6: note: 'snprintf' output between 2 and 6 bytes into a destination of size 4
snprintf(pvalue, 4, "%1d", ports[i]);
^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
cc1: all warnings being treated as errors
make[1]: *** [psm_ep.o] Error 1
make: *** [libs] Error 2


I want to suppress the error. It seems like this is a warning more than an error. Is that something I can do here? How would I do that?

2 Answers
2

It's treating that as an error because of the -Werror flag being passed to the compiler. That flag tells the compiler to turn any warnings into errors (see the cc1: all warnings being treated as errors) output line. Remove that flag to change the behavior (you'll probably have to edit the makefile).

-Werror

cc1: all warnings being treated as errors

WERROR := -Werror

buildflags.mak

WERROR := -Wno-error

Looks like a possible bug in the source, so it makes sense for the compiler to warn, especially with -Wall. (And with -Werror, this is treated as an error.)

-Wall

-Werror

"%1d" is never different from "%d": setting the minimum width to 1 is 1 redundant. (I didn't find an SO Q&A about it, but see http://www.kurabiyeaski.com/ym/201501/a_Meaning_of__1d_in_printf_statement_in__c__.html).

"%1d"

"%d"

"%.1d" would also be redundant: it sets the minimum number of digits to 1 (http://man7.org/linux/man-pages/man3/printf.3.html), but %d already always prints at least 1 digit and maybe a sign.

"%.1d"

%d

Anyway, this may indicated that the programmer who wrote this code intended something else, like perhaps only printing a single digit. You can't truncate integer formats with printf, as far as I know, so you'd have to use ports[i] % 10 if you want the last decimal digit, for example.

printf

ports[i] % 10

I'd recommend changing the format string to "%d" and submitting a patch to the authors.

"%d"

However, snprintf does 0-terminate the string even when it's too big for the buffer, so can safely use the truncated output as a C string. Unlike strncpy().

snprintf

strncpy()

This means it's safe to ignore this warning as long as the program does work correctly. It's not a crash or buffer overrun waiting to happen.

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