[Issue 23494] New: C-style variadic functions not working correctly

[d-bugmail at puremagic.com]

https://issues.dlang.org/show_bug.cgi?id=23494

          Issue ID: 23494
           Summary: C-style variadic functions not working correctly
           Product: D
           Version: D2
          Hardware: x86_64
                OS: Windows
            Status: NEW
          Severity: normal
          Priority: P1
         Component: dmd
          Assignee: nobody at puremagic.com
          Reporter: ogion.art at gmail.com

extern (C) void variadic(int* p, int x, int y, int z, const char *fmt, ...) {
    import core.stdc.stdarg;
    import core.stdc.stdio;

    va_list args;
    va_start(args, fmt);
    foreach (_; 0..2) {
        char* c;
        va_arg(args, c);
        printf("%s\n", c);
    }
    va_end(args);
}

void main() {
    variadic(null, 0, 0, 0, "%s %s", "one".ptr, "two".ptr);
}

This should print:
one
two

On Windows, this works correctly in a 32-bit build. When compiled with -m64
flag, this prints:
%s %s
one

Tinkering with parameters preceding `fmt` affects the output.

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