1 files changed, 92 insertions, 0 deletions
diff --git a/contrib/syslinux-4.02/gpxe/src/arch/i386/interface/pcbios/biosint.c b/contrib/syslinux-4.02/gpxe/src/arch/i386/interface/pcbios/biosint.c
new file mode 100644
index 0000000..a193def
--- /dev/null
+++ b/contrib/syslinux-4.02/gpxe/src/arch/i386/interface/pcbios/biosint.c
@@ -0,0 +1,92 @@
+#include <errno.h>
+#include <realmode.h>
+#include <biosint.h>
+
+/**
+ * @file BIOS interrupts
+ *
+ */
+
+FILE_LICENCE ( GPL2_OR_LATER );
+
+/**
+ * Hook INT vector
+ *
+ * @v interrupt		INT number
+ * @v handler		Offset within .text16 to interrupt handler
+ * @v chain_vector	Vector for chaining to previous handler
+ *
+ * Hooks in an i386 INT handler.  The handler itself must reside
+ * within the .text16 segment.  @c chain_vector will be filled in with
+ * the address of the previously-installed handler for this interrupt;
+ * the handler should probably exit by ljmping via this vector.
+ */
+void hook_bios_interrupt ( unsigned int interrupt, unsigned int handler,
+			   struct segoff *chain_vector ) {
+	struct segoff vector = {
+		.segment = rm_cs,
+		.offset = handler,
+	};
+
+	DBG ( "Hooking INT %#02x to %04x:%04x\n",
+	      interrupt, rm_cs, handler );
+
+	if ( ( chain_vector->segment != 0 ) ||
+	     ( chain_vector->offset != 0 ) ) {
+		/* Already hooked; do nothing */
+		DBG ( "...already hooked\n" );
+		return;
+	}
+
+	copy_from_real ( chain_vector, 0, ( interrupt * 4 ),
+			 sizeof ( *chain_vector ) );
+	DBG ( "...chaining to %04x:%04x\n",
+	      chain_vector->segment, chain_vector->offset );
+	if ( DBG_LOG ) {
+		char code[64];
+		copy_from_real ( code, chain_vector->segment,
+				 chain_vector->offset, sizeof ( code ) );
+		DBG_HDA ( *chain_vector, code, sizeof ( code ) );
+	}
+
+	copy_to_real ( 0, ( interrupt * 4 ), &vector, sizeof ( vector ) );
+	hooked_bios_interrupts++;
+}
+
+/**
+ * Unhook INT vector
+ *
+ * @v interrupt		INT number
+ * @v handler		Offset within .text16 to interrupt handler
+ * @v chain_vector	Vector containing address of previous handler
+ *
+ * Unhooks an i386 interrupt handler hooked by hook_i386_vector().
+ * Note that this operation may fail, if some external code has hooked
+ * the vector since we hooked in our handler.  If it fails, it means
+ * that it is not possible to unhook our handler, and we must leave it
+ * (and its chaining vector) resident in memory.
+ */
+int unhook_bios_interrupt ( unsigned int interrupt, unsigned int handler,
+			    struct segoff *chain_vector ) {
+	struct segoff vector;
+
+	DBG ( "Unhooking INT %#02x from %04x:%04x\n",
+	      interrupt, rm_cs, handler );
+
+	copy_from_real ( &vector, 0, ( interrupt * 4 ), sizeof ( vector ) );
+	if ( ( vector.segment != rm_cs ) || ( vector.offset != handler ) ) {
+		DBG ( "...cannot unhook; vector points to %04x:%04x\n",
+		      vector.segment, vector.offset );
+		return -EBUSY;
+	}
+
+	DBG ( "...restoring to %04x:%04x\n",
+	      chain_vector->segment, chain_vector->offset );
+	copy_to_real ( 0, ( interrupt * 4 ), chain_vector,
+		       sizeof ( *chain_vector ) );
+
+	chain_vector->segment = 0;
+	chain_vector->offset = 0;
+	hooked_bios_interrupts--;
+	return 0;
+}