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Re: [PATCH] add attribute nonstring

Thanks for mentioning the problem with GCC 8. If the intent of __attribute__((__nonstring__)) is to consistently mark char arrays that are not necessarily null-terminated strings, then lots of data structures in the tzdb code would need to be marked with this attribute. For example, every member of tzfile.h's 'struct tzhead' would have the attribute, because they are all char arrays that might not be null-terminated.

Looking at the proposed glibc patch, it seems its intent is more modest. All it's trying to do is to pacify GCC 8 so that GCC doesn't complain about calls to strncpy and strncat. In that case, a simpler and cleaner fix for tzdb is to stop using strncpy and strncat. (I suspect that the main reason tzdb uses strncpy is that its code is so old that it predates the widespread availability of memcpy.) So I installed the attached patch into tzdb's zic.c and it should be part of the next tzdb release.

Perhaps you can this idea elsewhere in the rest of the glibc patch too. It would be a lot of work to consistently change glibc to use __attribute__((__nonstring__)) for its documented purpose. If glibc can avoid calling strncpy and strncat, it won't need __NONSTRING; if not, then I suggest changing this:

/* Describes a char array that is not necessarily a NUL-terminated
   string.  */
# define __NONSTRING __attribute__ ((__nonstring__))

to something more like this:

/* Describes a char array whose address can safely be passed as the first
   argument to strncpy and strncat, as the char array is not necessarily
   a NUL-terminated string.  */
# define __NONSTRING __attribute__ ((__nonstring__))

in sys/cdefs.h, so that the more-modest goal of the patch is clearer to the reader.

I'll CC: this to as a heads-up there.

Attachment: 0001-Port-to-GCC-8-Wstringop-truncation.txt
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