c, c++: Return 1 for __has_builtin(__builtin_va_arg) and __has_builtin(__builtin_c23_...

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.

2025-01-21  Jakub Jelinek  <jakub@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.

diff --git a/gcc/c/c-decl.cc b/gcc/c/c-decl.cc
index 314b118b7c8b32ad8f968d440f4c382a361c2b90..68d331b2250325f1298c53536109dd2910da2b40 100644 (file)
--- a/gcc/c/c-decl.cc
+++ b/gcc/c/c-decl.cc
@@ -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;

diff --git a/gcc/cp/cp-objcp-common.cc b/gcc/cp/cp-objcp-common.cc
index fc6c790ce1136f2dc7453e23115778d2d6e07ea2..8336d0bb8f7cb6b374d1e268e7a8be5dc2091b20 100644 (file)
--- a/gcc/cp/cp-objcp-common.cc
+++ b/gcc/cp/cp-objcp-common.cc
@@ -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:

diff --git a/gcc/testsuite/c-c++-common/cpp/has-builtin-4.c b/gcc/testsuite/c-c++-common/cpp/has-builtin-4.c
new file mode 100644 (file)
index 0000000..65d2b18
--- /dev/null
+++ b/gcc/testsuite/c-c++-common/cpp/has-builtin-4.c
@@ -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