Ilya Leoshkevich <i...@linux.ibm.com> writes: > v1: https://gcc.gnu.org/pipermail/gcc-patches/2020-June/548822.html > > This is the implementation of Richard's suggestion. I've decided not > to remove the initial #define NULL 0, since system.h mixes inclusion of > system and helper headers (e.g. libiberty), which might use NULL - if > not today, then in the future. If system headers do not provide NULL, > removing #define NULL 0 might lead to build errors. Ideally the order > should be: > > system headers > #undef NULL > #define NULL nullptr > helper headers > > but I fear that rearranging includes might break some weird system. > > This patch helps with alpine bootstrap, I'm currently testing it on > x86_64-redhat-linux. > > --- > > Bootstrap with musl libc fails with numerous "missing sentinel in > function call" errors. This is because musl defines NULL as 0L for C++, > but gcc requires sentinel value to be a pointer or __null. > > Jonathan Wakely says: > > To be really safe during stage 1, GCC should not use NULL as a > pointer sentinel in C++ code anyway. > > The bootstrap compiler could define it to 0 or 0u, neither of which > is guaranteed to be OK to pass as a varargs sentinel where a null > pointer is expected. Any of (void*)0 or (void*)NULL or nullptr > would be safe. > > While it is possible to fix this by replacing NULL sentinels with > nullptrs, such approach would generate backporting conflicts, therefore > simply redefine NULL to nullptr at the end of system.h, where it would > not confuse system headers. > > gcc/ChangeLog: > > 2020-06-30 Ilya Leoshkevich <i...@linux.ibm.com> > > PR bootstrap/95700 > * system.h (NULL): Redefine to nullptr.
LGTM, thanks. OK if noone objects in the next 24hrs. Richard > --- > gcc/system.h | 10 ++++++++++ > 1 file changed, 10 insertions(+) > > diff --git a/gcc/system.h b/gcc/system.h > index 544f7ba427f..1eec77e730e 100644 > --- a/gcc/system.h > +++ b/gcc/system.h > @@ -1244,4 +1244,14 @@ void gcc_stablesort (void *, size_t, size_t, > of the number. */ > #define PRsa(n) "%" #n PRIu64 "%c" > > +/* System headers may define NULL to be an integer (e.g. 0L), which cannot be > + used safely in certain contexts (e.g. as sentinels). Redefine NULL to > + nullptr in order to make it safer. Note that this might confuse system > + headers, however, by convention they must not be included after this > point. > +*/ > +#ifdef __cplusplus > +#undef NULL > +#define NULL nullptr > +#endif > + > #endif /* ! GCC_SYSTEM_H */
