--- ./sys/arch/amd64/stand/mbr/mbr.S.orig	2020-01-11 16:20:46.000000000 +0100
+++ ./sys/arch/amd64/stand/mbr/mbr.S	2020-01-11 18:01:44.000000000 +0100
@@ -416,12 +416,17 @@ do_lba:
 
 	popw	%si			/* (get back %si) flags unchanged */
 
-	jnc	booting_os		/* If it worked, run the pbr we got */
+	jnc	tpm_measure		/* If it worked, measure and run the pbr we got */
 
 	/*
 	 * LBA read failed, fall through to try CHS read
 	 */
 
+#ifdef NO_CHS
+do_chs:
+	movw	$enochs, %si
+	jmp	err_stop
+#else
 do_chs:
 	/*
 	 * BIOS call "INT 0x13 Function 0x2" to read sectors from disk into
@@ -451,11 +456,69 @@ do_chs:
 	movw	$0x201, %ax		/* function and number of blocks */
 	xorw	%bx, %bx		/* put it at %es:0 */
 	int	$0x13
-	jnc	booting_os
+	jnc	tpm_measure
 
 read_error:
 	movw	$eread, %si
 	jmp	err_stop
+#endif
+
+tpm_measure:
+#ifdef TPM_MEASURE
+	/*
+	 * BIOS call "INT 0x1a TCG_StatusCheck"
+	 *	On entry 	%ah = 0xBB
+	 * 			%al = 0x00
+	 *	On return:
+	 * 			%eax = returncode, set to 0 if supported
+	 *			%ebx = 0x41504353
+	 *			%ch  = TCG BIOS Major Version
+	 *			%cl  = TCG BIOS Minor Version
+	 *			%edx = BIOS TCG Feature Flags
+	 *			%esi = absolute pointer to event log
+	 *			%edi = pointer to eventlog
+	 * From: TCG PC Client Specific Implementation Specification for
+	 *       Conventional BIOS (Version 1.20 FINAL, July 13, 2005)
+	 */
+        pushl   %edx            /* dl contains bios drive number -> preserve */
+
+	movw	$0xbb00, %ax
+	int	$0x1a
+	test	%eax, %eax
+	jnz	measure_end
+	cmpw	$0x4354, %bx
+	jnz	measure_end
+
+	/*
+	 * BIOS call "INT 0x1a TCG_CompactHashLogExtendEvent"
+	 *	On entry 	%ah  = 0xBB
+	 * 			%al  = 0x07
+	 *			%es  = Segment portion of buffer to be hashed
+	 *			%di  = Offset  portion of buffer to be hashed
+	 *			%esi = The informative value for event field
+	 *			%ebx = 0x41504354
+	 *			%ecx = Length in bytes of the buffer to be hashed
+	 *			%edx = The PCRIndex to be extended
+	 *	On return:
+	 *			%eax = Return Code as defined in section
+	 *			%edx = event number of the event that was logged
+	 *			All other registers are preserved
+	 *
+	 * From: TCG PC Client Specific Implementation Specification for
+	 *       Conventional BIOS (Version 1.20 FINAL, July 13, 2005)
+	 */
+	movw	$0xbb07, %ax
+	xorw	%di, %di
+	xorl	%esi, %esi
+	movl	$0x41504354, %ebx
+	movl    $0x200, %ecx
+        xorl    %edx, %edx      /* doing xorl + movb saves 1 byte */
+        movb    $0x08,  %dl
+	int	$0x1a
+
+measure_end:
+        popl   %edx
+#endif
 
 booting_os:
 	puts(crlf)
@@ -532,7 +595,11 @@ part_num:
 
 /* Error messages */
 efdmbr:	.asciz		"MBR on floppy or old BIOS\r\n"
+#if NO_CHS
+enochs:	.asciz		"\r\nCompiled w/o chs\r\n"
+#else
 eread:	.asciz		"\r\nRead error\r\n"
+#endif
 enoos:	.asciz		"No O/S\r\n"
 enoboot: .ascii		"No active partition"	/* runs into crlf... */
 crlf:	.asciz		"\r\n"