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The generic definitions here must not be used. */ > > +void __libc_mtag_link_error (void); > > This may make it impossible to compile individual glibc modules with > -O0, say, for debugging purposes. I do this quite often with malloc.c > and do not want to lose that ability. > > Do we trust the compiler's default optimizations (at -O0) to do code > elimination based on constant conditions? yes, this breaks -O0, i haven't thought of that. i thought it's better to guard everything with one flag in the code than ifdefs (that can be runtime flag with tagging enabled or constant 0 when disabled) since ifdefed code is not checked by the compiler. the link error is to ensure that without tagging the tagging hooks are not called accidentally. i can replace that with abort() and then -O0 works but then you only get runtime failure, not a link time one (which is less useful since it may be in a very rarely used code path). alternatively i can remove this safety net or just go back to ifdefs.