Author: Aaron Ballman Date: 2025-03-12T14:38:54-04:00 New Revision: ab53e1c8e52388377ba50c05979b03a691513cfd
URL: https://github.com/llvm/llvm-project/commit/ab53e1c8e52388377ba50c05979b03a691513cfd DIFF: https://github.com/llvm/llvm-project/commit/ab53e1c8e52388377ba50c05979b03a691513cfd.diff LOG: [C2y] Claim conformance to WG14 N3363 (#130980) This paper clarifies two things: * a call to va_start must be within the body of a variadic function, * the va_list arguments must be lvalues Clang has correctly diagnosed the first point since Clang 5.0. Clang generally diagnoses the second point, except for va_copy. However, the second point is not a constraint violation, so a diagnostic is not strictly required. That said, it would be good for us to properly diagnose va_copy. Added: clang/test/C/C2y/n3363.c Modified: clang/www/c_status.html Removed: ################################################################################ diff --git a/clang/test/C/C2y/n3363.c b/clang/test/C/C2y/n3363.c new file mode 100644 index 0000000000000..2ad0241a74c60 --- /dev/null +++ b/clang/test/C/C2y/n3363.c @@ -0,0 +1,40 @@ +// RUN: %clang_cc1 -triple x86_64-pc-linux -verify=expected,array-type -std=c2y -Wall -pedantic -ffreestanding %s +// RUN: %clang_cc1 -triple aarch64-pc-win32 -verify=expected,char-ptr-type -std=c2y -Wall -pedantic -ffreestanding %s + +/* WG14 N3363: Clang 5 + * stdarg.h wording... v3 + * + * Clarifies that va_start can only be used within a function body, and that + * the macros and functions require an lvalue of type va_list instead of an + * rvalue. + * + * Clang has diagnosed this correctly in all cases except va_copy since + * Clang 5. va_copy still needs to be updated to issue a diagnostic about use + * of an rvalue. However, our lack of a diagnostic is still conforming because + * a diagnostic is not required (it's not a constraint violation). + */ + +#include <stdarg.h> + +// The va_list argument given to every macro defined in this subclause shall be +// an lvalue of this type or the result of array-to-pointer decay of such an +// lvalue. +void f(int a, ...) { + va_list rvalue(); // array-type-error {{function cannot return array type 'va_list' (aka '__builtin_va_list')}} + va_start(rvalue()); // / char-ptr-type-error {{non-const lvalue reference to type '__builtin_va_list' cannot bind to a temporary of type 'va_list' (aka 'char *')}} + va_arg(rvalue(), int); // char-ptr-type-error {{expression is not assignable}} + // FIXME: this should get two diagnostics about use of a non-lvalue. + va_copy(rvalue(), rvalue()); // char-ptr-type-error {{non-const lvalue reference to type '__builtin_va_list' cannot bind to a temporary of type 'va_list' (aka 'char *')}} + va_end(rvalue()); // char-ptr-type-error {{non-const lvalue reference to type '__builtin_va_list' cannot bind to a temporary of type 'va_list' (aka 'char *')}} +} + +// The va_start macro may only be invoked in the compound-statement of the body +// of a variadic function. +void g(va_list ap, int [(va_start(ap), 1)], ...) { // expected-error {{'va_start' cannot be used outside a function}} + va_end(ap); +} + +va_list ap; +struct S { + int array[(va_start(ap), 1)]; // expected-error {{'va_start' cannot be used outside a function}} +}; diff --git a/clang/www/c_status.html b/clang/www/c_status.html index 4432e62b47520..6080ed060cfbb 100644 --- a/clang/www/c_status.html +++ b/clang/www/c_status.html @@ -263,7 +263,7 @@ <h2 id="c2y">C2y implementation status</h2> <tr> <td>stdarg.h wording... v3</td> <td><a href="https://www.open-std.org/jtc1/sc22/wg14/www/docs/n3363.pdf";>N3363</a></td> - <td class="unknown" align="center">Unknown</td> + <td class="full" align="center">Clang 5</td> </tr> <tr> <td>Preprocessor integer expressions, v. 2</td> _______________________________________________ cfe-commits mailing list cfe-commits@lists.llvm.org https://lists.llvm.org/cgi-bin/mailman/listinfo/cfe-commits
