On 1/19/23 3:36 PM, Jessica Clarke wrote:
On 19 Jan 2023, at 23:31, Jessica Clarke <[email protected]> wrote:
On 19 Jan 2023, at 23:11, Jessica Clarke <[email protected]> wrote:
On 19 Jan 2023, at 22:49, John Baldwin <[email protected]> wrote:
The branch main has been updated by jhb:
URL:
https://cgit.FreeBSD.org/src/commit/?id=43703bc489ec504b947b869045c492ed38c1a69c
commit 43703bc489ec504b947b869045c492ed38c1a69c
Author: John Baldwin <[email protected]>
AuthorDate: 2023-01-19 22:48:52 +0000
Commit: John Baldwin <[email protected]>
CommitDate: 2023-01-19 22:48:52 +0000
stdlib.h: Fix qsort_r compatibility with GCC 12.
GCC 12 (unlike GCC 9) does not match a function argument passed to the
old qsort_r() API (as is used in the qsort_r_compat test) to a
function pointer type via __generic. It treats the function type as a
distinct type from a function pointer. As a workaround, add a second
definition of qsort_r for GCC 12 which uses the bare function type.
As far as I can tell both versions of GCC behave the same. The
difference is whether __generic is using _Generic or
__builtin_choose_expr with __builtin_types_compatible_p, since function
and function pointer types are not compatible. Clang will take the
__has_extension path, but GCC will take the builtins path, and so Clang
works but GCC doesn’t.
As a result of this change you’ve likely broken code that does
qsort_r(..., &f) as that will have the opposite problem. The right fix
is to force arg5 to decay, such as by (ab)using the comma operator with
__generic((0, arg5), ...). I guess that probably belongs in the
fallback implementation of __generic though, not here, which would give
the following real fix:
diff --git a/sys/sys/cdefs.h b/sys/sys/cdefs.h
index 83ba7584e5b9..f7eff4768151 100644
--- a/sys/sys/cdefs.h
+++ b/sys/sys/cdefs.h
@@ -312,6 +312,9 @@
* __generic(). Unlike _Generic(), this macro can only distinguish
* between a single type, so it requires nested invocations to
* distinguish multiple cases.
+ *
+ * Note that the comma operator is used to force expr to decay in order to
+ * match _Generic.
*/
#if (defined(__STDC_VERSION__) && __STDC_VERSION__ >= 201112L) || \
@@ -321,7 +324,7 @@
#elif __GNUC_PREREQ__(3, 1) && !defined(__cplusplus)
#define __generic(expr, t, yes, no) \
__builtin_choose_expr( \
- __builtin_types_compatible_p(__typeof(expr), t), yes, no)
+ __builtin_types_compatible_p(__typeof((0, expr)), t), yes, no)
With (expr) instead of expr, of course...
And as for why GCC 9 works:
It doesn’t. The tests just aren’t built because MK_CXX=no disables
MK_TESTS. GCC 12 only hits it because it’s new enough to be able to
build libc++ and not force MK_CXX=no.
It would be nice to unpick that...
Hmm, ok I thought I had managed to build this test with GCC 9 previously, but
perhaps not.
I will give the cdefs.h change a go locally though and see what happens.
--
John Baldwin
