Initial revision

src/arch/i386/firmware/pcbios/hidemem.c

@@ -0,0 +1,94 @@
+/* Utility functions to hide Etherboot by manipulating the E820 memory
+ * map.  These could go in memsizes.c, but are placed here because not
+ * all images will need them.
+ */
+
+#include "etherboot.h"
+#include "hidemem.h"
+
+#ifdef	CODE16
+
+static int mangling = 0;
+static void *mangler = NULL;
+
+#define INSTALLED(x)	( (typeof(&x)) ( (void*)(&x) - (void*)e820mangler \
+					 + mangler ) )
+#define intercept_int15		INSTALLED(_intercept_int15)
+#define intercepted_int15	INSTALLED(_intercepted_int15)
+#define hide_memory		INSTALLED(_hide_memory)
+#define INT15_VECTOR ( (segoff_t*) ( phys_to_virt( 4 * 0x15 ) ) )
+
+int install_e820mangler ( void *new_mangler ) {
+	if ( mangling ) return 0;
+	memcpy ( new_mangler, &e820mangler, e820mangler_size );
+	mangler = new_mangler;
+	return 1;
+}
+
+/* Intercept INT15 calls and pass them through the mangler.  The
+ * mangler must have been copied to base memory before making this
+ * call, and "mangler" must point to the base memory copy, which must
+ * be 16-byte aligned.
+ */
+int hide_etherboot ( void ) {
+	if ( mangling ) return 1;
+	if ( !mangler ) return 0;
+
+	/* Hook INT15 handler */
+	*intercepted_int15 = *INT15_VECTOR;
+	(*hide_memory)[0].start = virt_to_phys(_text);
+	(*hide_memory)[0].length = _end - _text;
+	/* IMPORTANT, possibly even FIXME:
+	 *
+	 * Etherboot has a tendency to claim a very large area of
+	 * memory as possible heap; enough to make it impossible to
+	 * load an OS if we hide all of it.  We hide only the portion
+	 * that's currently in use.  This means that we MUST NOT
+	 * perform further allocations from the heap while the mangler
+	 * is active.
+	 */
+	(*hide_memory)[1].start = heap_ptr;
+	(*hide_memory)[1].length = heap_bot - heap_ptr;
+	INT15_VECTOR->segment = SEGMENT(mangler);
+	INT15_VECTOR->offset = 0;
+
+	mangling = 1;
+	return 1;
+}
+
+int unhide_etherboot ( void ) {
+	if ( !mangling ) return 1;
+
+	/* Restore original INT15 handler
+	 */
+	if ( VIRTUAL(INT15_VECTOR->segment,INT15_VECTOR->offset) != mangler ) {
+		/* Oh dear... */
+
+#ifdef WORK_AROUND_BPBATCH_BUG
+		/* BpBatch intercepts INT15, so can't unhook it, and
+		 * then proceeds to ignore our PXENV_KEEP_UNDI return
+		 * status, which means that it ends up zeroing out the
+		 * INT15 handler routine.
+		 *
+		 * This rather ugly hack involves poking into
+		 * BpBatch's code and changing it's stored value for
+		 * the "next handler" in the INT15 chain.
+		 */
+		segoff_t *bp_chain = VIRTUAL ( 0x0060, 0x8254 );
+
+		if ( ( bp_chain->segment == SEGMENT(mangler) ) &&
+		     ( bp_chain->offset == 0 ) ) {
+			printf ( "\nBPBATCH bug workaround enabled\n" );
+			*bp_chain = *intercepted_int15;
+		}
+#endif /* WORK_AROUND_BPBATCH_BUG */
+
+		return 0;
+	}
+	*INT15_VECTOR = *intercepted_int15;
+
+	mangling = 0;
+	return 1;
+}
+
+#endif	/* CODE16 */