Remove vcruntime140.dll dependency

This will save users having to install the VS runtime in order to load
the plugin. Turns out there was very little to implement to make this
work.

Turning off stack probing might cause spooky outcomes further down the
line but we'll burn that bridge when we get there.

1 files changed, 48 insertions, 0 deletions

diff --git a/src/wincrt.c b/src/wincrt.c
new file mode 100644
index 0000000..8ffa6cb
--- /dev/null
+++ b/src/wincrt.c
@@ -0,0 +1,48 @@
+/* This file is dedicated to the public domain. */
+
+// We get most of the libc functions from ucrtbase.dll, which comes with
+// Windows, but for some reason a few of the intrinsic-y things are part of
+// vcruntime, which does *not* come with Windows!!! We can statically link just
+// that part but it adds ~12KiB of random useless bloat to our binary. So, let's
+// just implement the handful of required things here instead. This is only for
+// release/non-debug builds; we want the extra checks in Microsoft's CRT when
+// debugging.
+//
+// Is it actually reasonable to have to do any of this? Of course not.
+
+// TODO(opt): this feels like a sad implementation, can we do marginally better?
+int memcmp(const void *x_, const void *y_, unsigned int sz) {
+	const char *x = x_, *y = y_;
+	for (unsigned int i = 0; i < sz; ++i) {
+		if (x[i] > y[i]) return 1;
+		if (x[i] < y[i]) return -1;
+	}
+	return 0;
+}
+
+void *memcpy(void *restrict x, const void *restrict y, unsigned int sz) {
+#ifdef __clang__
+	__asm__ volatile (
+		"rep movsb\n" :
+		"=D" (x), "=S" (y), "=c" (sz) :
+		"0" (x), "1" (y), "2" (sz) :
+		"memory"
+	);
+#else // terrible fallback just in case someone wants to use this with MSVC
+	char *restrict xb = x; const char *restrict yb = y;
+	for (unsigned int i = 0; i < sz; ++i) xb[i] = yb[i];
+#endif
+	return x;
+}
+
+int __stdcall _DllMainCRTStartup(void *inst, unsigned int reason,
+		void *reserved) {
+	return 1;
+}
+
+#ifdef __clang__
+__attribute__((used))
+#endif
+int _fltused = 1;
+
+// vi: sw=4 ts=4 noet tw=80 cc=80