AArch64: Compile error in trclog.c with strncpy()

[knn-k]

I got the following error while I was compiling for linux_aarch64. It is similar to Issue #3242.

aarch64-linux-gnu-gcc -U_FORTIFY_SOURCE -D_FORTIFY_SOURCE=1 -DOPENJ9_BUILD -O -fgnu89-inline -g -DLINUX -D_REENTRANT -D_FILE_OFFSET_BITS=64 -fpic -DIPv6_FUNCTION_SUPPORT -DJ9AARCH64 -Wimplicit -Wreturn-type -Werror -Wall -I. -I../include -I../oti -I../gc_include -I../omr/gc/include -I../nls -I../omr/include_core    -DUT_DIRECT_TRACE_REGISTRATION -DTR_HOST_ARM64 -c -o trclog.o trclog.c
In file included from /root/gcc-linaro-7.3.1-2018.05-x86_64_aarch64-linux-gnu/aarch64-linux-gnu/libc/usr/include/string.h:639:0,
                 from ../omr/include_core/omrstdarg.h:27,
                 from trclog.c:26:
In function 'strncpy',
    inlined from 'getTrcBuf' at trclog.c:1063:3:
/root/gcc-linaro-7.3.1-2018.05-x86_64_aarch64-linux-gnu/aarch64-linux-gnu/libc/usr/include/bits/string3.h:125:10: error: '__builtin_strncpy' writing 512 bytes into a region of size 1 overflows the destination [-Werror=stringop-overflow=]
   return __builtin___strncpy_chk (__dest, __src, __len, __bos (__dest));
          ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
cc1: all warnings being treated as errors
../makelib/targets.mk:272: recipe for target 'trclog.o' failed

# aarch64-linux-gnu-gcc --version
aarch64-linux-gnu-gcc (Linaro GCC 7.3-2018.05) 7.3.1 20180425 [linaro-7.3-2018.05 revision d29120a424ecfbc167ef90065c0eeb7f91977701]

It compiles without the error when I remove -D_FORTIFY_SOURCE=1 from the command-line option.

[gacholio]

I suspect a cast of the dest to void* in the caller would fix this.

[knn-k]

No, casting the destination to void * does not change the error.
I will use --disable-warnings-as-errors-openj9 in configure for the time being.

[dnakamura]

interesting. On other linux platforms this only shows up when _FORTIFY_SOURCE >=2. I believe the only way to deal with it (other than modifying _FORTIFY_SOURCE) is to avoid strncpy

[sxa]

@dnakamura What are the implications of modifying _FORTIFY_SOURCE?

[dnakamura]

It adds extra checks to c string manipulation functions.

http://man7.org/linux/man-pages/man7/feature_test_macros.7.html :

_FORTIFY_SOURCE (since glibc 2.3.4)

Defining this macro causes some lightweight checks to be per formed to detect some buffer overflow errors when employing various string and memory manipulation functions (for example, memcpy(3),memset(3), stpcpy(3), strcpy(3), strncpy(3),strcat(3), strncat(3), sprintf(3), snprintf(3), vsprintf(3),vsnprintf(3), gets(3), and wide character variants thereof). For some functions, argument consistency is checked; for example, a check is made that open(2) has been supplied with a mode argument when the specified flags include O_CREAT. Not all problems are detected, just some common cases.

If _FORTIFY_SOURCE is set to 1, with compiler optimization level 1 (gcc -O1) and above, checks that shouldn't change the behavior of conforming programs are performed. With _FORTIFY_SOURCE set to 2, some more checking is added, but some conforming programs might fail.
Some of the checks can be performed at compile time (via macros logic implemented in header files), and result in compiler warnings; other checks take place at run time, and result in a run-time error if the check fails.

Use of this macro requires compiler support, available with gcc(1) since version 4.0.

[knn-k]

Is it possible to add or change compiler options only for trclog.c?

[dnakamura]

@knn-k

Is it possible to add or change compiler options only for trclog.c?

I think so, yes. I think this should work (although I haven't tested)

<makefilestubs>
    <makefilestub data="trclog.o: CFLAGS+=-U_FORTIFY_SOURCE"/>
</makefilestubs>

[knn-k]

@dnakamura Thank you, it works. I apply it to #5508.