betterC not able to use core.stdc.stdarg

[dlangBugzillaToGithub]

Derek Fawcus reported this on 2024-10-14T20:28:44Z

Transferred from https://issues.dlang.org/show_bug.cgi?id=24814

Description

Created attachment 1920
Patch to fix the library file

Trying to use va_end() or va_copy() from a betterC program fails due to missing symbols.  See this forum thread: https://forum.dlang.org/post/veackr$2n3c$1@digitalmars.com

This was with 'DMD64 D Compiler v2.109.1'.  These stdarg issues do not arise with GDC or LDC as they make use of compiler intrinsics, not actual functions with bodies.

stdarg1.d:
```d
import core.stdc.stdarg;

pragma(printf)
public extern(C) int wrap_printf(scope const char* f, ...) {
	import core.stdc.stdio;

	va_list ap;

	va_start(ap, f);
	auto rc = vprintf(f, ap);
	va_end(ap);

	return rc;
}

extern(C) void main() {
	wrap_printf("Foo
");
}
```

```
$ dmd -betterC stdarg1.d
/usr/bin/ld: stdarg1.o: in function `wrap_printf':
stdarg1.d:(.text.wrap_printf[wrap_printf]+0xce): undefined reference to `_D4core4stdc6stdarg6va_endFNbNiPSQBf8internal6vararg8sysv_x6413__va_list_tagZv'
collect2: error: ld returned 1 exit status
Error: undefined reference to `nothrow @nogc void core.stdc.stdarg.va_end(core.internal.vararg.sysv_x64.__va_list_tag*)`
       referenced from `wrap_printf`
       perhaps `.d` files need to be added on the command line, or use `-i` to compile imports
Error: linker exited with status 1
       cc stdarg1.o -o stdarg1 -m64 -Xlinker --export-dynamic -L/usr/lib/x86_64-linux-gnu -lpthread -lm -lrt -ldl
```

A similar issue arises if one tries to use va_copy().

The thread mentions a couple of workarounds, applying these makes things work.  However I attach a patch which makes va_end() and va_copy() work (for -m32), but only va_end() for -m64.

That is because va_copy() on x64 requires the use of alloca(), and that is also not satisfied when compiling with -betterC, however that can be a different ticket.

The va_copy issue can be demonstrated with this modified version, and differences between -m32 and -m64 observed even when the patch is applied to the library source file.

stdarg1a:
```d
import core.stdc.stdarg;

pragma(printf)
public extern(C) int wrap_printf(scope const char* f, ...) {
	import core.stdc.stdio;

	va_list ap, ap2;

	va_start(ap, f);
	va_copy(ap2, ap);
	auto rc = vprintf(f, ap);
	va_end(ap2);
	va_end(ap);

	return rc;
}

extern(C) void main() {
	wrap_printf("Foo
");
}
```

!!!There are attachements in the bugzilla issue that have not been copied over!!!