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.
---
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 */
--
2.25.4
