[Bug libc/16640] New: string/strtok.c: undefined behaviour inconsistent between x86 and other generic code

["kyle at redhat dot com" <sourceware-bugzilla at sourceware dot org>]

https://sourceware.org/bugzilla/show_bug.cgi?id=16640

            Bug ID: 16640
           Summary: string/strtok.c: undefined behaviour inconsistent
                    between x86 and other generic code
           Product: glibc
           Version: unspecified
            Status: NEW
          Severity: minor
          Priority: P2
         Component: libc
          Assignee: unassigned at sourceware dot org
          Reporter: kyle at redhat dot com
                CC: drepper.fsp at gmail dot com

Created attachment 7444
  --> https://sourceware.org/bugzilla/attachment.cgi?id=7444&action=edit
make string/strtok match x86

The strtok.S implementations for x86_64 and i386 vary from the generic
string/strtok.c version. In the former case, if str == NULL, and the saved
string is also NULL, the strtok call returns NULL.

In contrast, the string/strtok.c call proceeds to pass s = olds = NULL to
strspn which consequently crashes.

While this behaviour is probably permissible, it results in odd portability
issues where the behaviour can't be reproduced on x86_64. As well, the generic
versions in the BSD libc I looked at (which appears to date back to 4.3BSD or
earlier...) also checks for the (s = olds) == NULL condition and handles it, so
we have a bit of precedent here.

Attached is a patch which brings the generic string/strtok.c in-line with i386,
x86_64 and BSD. It seems better to do that, rather than suddenly make working
code SIGSEGV on x86_64...

regards, Kyle

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