[9front] vmx vs openbsd-current bsd.rd

[ori@eigenstate.org]

It seems that some time around the OpenBSD 6.9 release,
bsd.rd ended up getting compressed, and losing most of
its symbols; now, our heuristics for image detection
fail to detect it. We used to expect an 'ostype' elf
symbol that contained OpenBSD, but that's only present
on the bsd, bsd.mp kernels:

	$ nm bsdSNAP.rd                                                                                                            	ffffffff81532ba0 D rd_root_image
	ffffffff81532b90 D rd_root_size

So, I hacked up the kernel detection heuristic. Still,
this feels a bit gross.

Does anyone have any better options?

diff 8f4842d3465e96d264f5c2f7fa2d61db871aae9f uncommitted
--- a/sys/src/cmd/vmx/ksetup.c
+++ b/sys/src/cmd/vmx/ksetup.c
@@ -728,7 +728,7 @@
 static int
 tryelf(void)
 {
-	char *s;
+	char *s, *t;
 
 	if(!elfheaders()) return 0;
 	elfdata();
@@ -735,6 +735,11 @@
 	if(!elfsymbols()) return 0;
 	s = symaddr(elfsym("ostype"));
 	if(s != nil && strcmp(s, "OpenBSD") == 0)
+		return obsdload();
+	/* from 6.9 up, bsd.rd has just these syms */
+	s = symaddr(elfsym("rd_root_image"));
+	t = symaddr(elfsym("rd_root_size"));
+	if(s != nil && t != nil)
 		return obsdload();
 	return 0;
 }