Hi!
The Linux kernel uses its own copy of stdarg.h.
Now, before GCC 15, our stdarg.h had
#if defined __STDC_VERSION__ && __STDC_VERSION__ > 201710L
#define va_start(v, ...) __builtin_va_start(v, 0)
#else
#define va_start(v,l) __builtin_va_start(v,l)
#endif
va_start definition but GCC 15 has:
#if defined __STDC_VERSION__ && __STDC_VERSION__ > 201710L
#define va_start(...) __builtin_c23_va_start(__VA_ARGS__)
#else
#define va_start(v,l) __builtin_va_start(v,l)
#endif
I wanted to suggest to the kernel people during their porting to C23
that they'd better use C23 compatible va_start macro definition,
but to make it portable, I think they really want something like
#if defined __STDC_VERSION__ && __STDC_VERSION__ > 201710L
#define va_start(v, ...) __builtin_va_start(v, 0)
#ifdef __has_builtin
#if __has_builtin(__builtin_c23_va_start)
#undef va_start
#define va_start(...) __builtin_c23_va_start(__VA_ARGS__)
#endif
#else
#define va_start(v,l) __builtin_va_start(v,l)
#endif
or so (or with >= 202311L), as GCC 13-14 and clang don't support
__builtin_c23_va_start (yet?) and one gets better user experience with
that.
Except it seems __has_builtin(__builtin_c23_va_start) doesn't actually work,
it works for most of the stdarg.h __builtin_va_*, doesn't work for
__builtin_va_arg (neither C nor C++) and didn't work for
__builtin_c23_va_start if it was available.
The following patch wires __has_builtin for those.
Bootstrapped on x86_64-linux and i686-linux, regtest ongoing, ok for trunk
if it passes?
2025-01-17 Jakub Jelinek <ja...@redhat.com>
gcc/c/
* c-decl.cc (names_builtin_p): Return 1 for RID_C23_VA_START and
RID_VA_ARG.
gcc/cp/
* cp-objcp-common.cc (names_builtin_p): Return 1 for RID_VA_ARG.
gcc/testsuite/
* c-c++-common/cpp/has-builtin-4.c: New test.
--- gcc/c/c-decl.cc.jj 2025-01-17 11:29:33.276694451 +0100
+++ gcc/c/c-decl.cc 2025-01-17 15:13:44.497856864 +0100
@@ -11804,6 +11804,8 @@ names_builtin_p (const char *name)
case RID_CHOOSE_EXPR:
case RID_OFFSETOF:
case RID_TYPES_COMPATIBLE_P:
+ case RID_C23_VA_START:
+ case RID_VA_ARG:
return 1;
default:
break;
--- gcc/cp/cp-objcp-common.cc.jj 2025-01-02 11:47:10.703494721 +0100
+++ gcc/cp/cp-objcp-common.cc 2025-01-17 15:16:07.218885238 +0100
@@ -587,6 +587,7 @@ names_builtin_p (const char *name)
case RID_BUILTIN_ASSOC_BARRIER:
case RID_BUILTIN_BIT_CAST:
case RID_OFFSETOF:
+ case RID_VA_ARG:
return 1;
case RID_BUILTIN_OPERATOR_NEW:
case RID_BUILTIN_OPERATOR_DELETE:
--- gcc/testsuite/c-c++-common/cpp/has-builtin-4.c.jj 2025-01-17
15:15:44.077204928 +0100
+++ gcc/testsuite/c-c++-common/cpp/has-builtin-4.c 2025-01-17
15:15:02.520779011 +0100
@@ -0,0 +1,16 @@
+/* { dg-do preprocess } */
+
+#if __has_builtin (__builtin_va_start) != 1
+#error "No __builtin_va_start"
+#endif
+#if __has_builtin (__builtin_va_end) != 1
+#error "No __builtin_va_end"
+#endif
+#if __has_builtin (__builtin_va_arg) != 1
+#error "no __builtin_va_arg"
+#endif
+#if __STDC_VERSION__ >= 202311L
+#if __has_builtin (__builtin_c23_va_start) != 1
+#error "no __builtin_c23_va_start"
+#endif
+#endif
Jakub
