https://gcc.gnu.org/bugzilla/show_bug.cgi?id=118435
Bug ID: 118435
Summary: __builtin_va_arg does not check for POD type argument
when it is passed by value
Product: gcc
Version: 15.0
Status: UNCONFIRMED
Severity: normal
Priority: P3
Component: c++
Assignee: unassigned at gcc dot gnu.org
Reporter: wangbopku15 at gmail dot com
Target Milestone: ---
Consider the following code:
$g++ -Wall -Wextra
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
#include <stdarg.h>
struct S {
private:
virtual void foo();
};
struct S arg;
void
foo (int z, ...)
{
va_list ap;
va_start (ap, z);
arg = va_arg (ap, struct S);
va_end (ap);
}
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
Clang rejects it and the diagnostic reveals that the argument of 'va_arg' must
be a POD type when it is passed by value:
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
<source>:14:21: error: second argument to 'va_arg' is of non-POD type 'struct
S' [-Wnon-pod-varargs]
14 | arg = va_arg (ap, struct S);
| ^~~~~~~~
/opt/compiler-explorer/clang-trunk-20250112/lib/clang/20/include/__stdarg_va_arg.h:20:47:
note: expanded from macro 'va_arg'
20 | #define va_arg(ap, type) __builtin_va_arg(ap, type)
| ^~~~
1 error generated.
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
It seems that GCC does not have the corresponding restriction as the compiler
always accepts the code despite under options like '-Wall -Wextra':
https://godbolt.org/z/nKhMK54rW
