vmm_x86: guest code page in separate asm file

Implement the guest code in dedicated assembler source file, assemble
and link the binary to vmm_x86. The resulting guest-code binary
populates one page that is mapped to host the reset vector of the guest.

This approach simplifies future guest code adaption resp. extension,
e.g., to test rdmsr/wrmsr exiting.

Fixes #4638

repos/os/run/vmm_x86.run

@@ -208,7 +208,7 @@ compare_output_to {
 [init -> vmm] vcpu 0 : created
 vcpu 0 : XX. vm exit - reason 0xfe handled by 'ep'
 vcpu 0 : XX. vm exit - reason 0x78 handled by 'ep'
-vcpu 0 : XX. vm exit -  halting vCPU - guest called HLT - ip=0xfff3
+vcpu 0 : XX. vm exit -  halting vCPU - guest called HLT - ip=0xff81
 }
 
 puts $output_1
@@ -217,19 +217,19 @@ compare_output_to {
 [init -> vmm] vcpu 1 : created
 vcpu 1 : XX. vm exit - reason 0xfe handled by 'ep'
 vcpu 1 : XX. vm exit - reason 0x78 handled by 'ep'
-vcpu 1 : XX. vm exit -  halting vCPU - guest called HLT - ip=0xfff3
+vcpu 1 : XX. vm exit -  halting vCPU - guest called HLT - ip=0xff81
 vcpu 1 : XX. vm exit - reason 0xff handled by 'ep'
-vcpu 1 : XX. vm exit -  due to pause() request - ip=0xfff3
+vcpu 1 : XX. vm exit -  due to pause() request - ip=0xff81
 vcpu 1 : XX. vm exit - reason 0x78 handled by 'ep'
-vcpu 1 : XX. vm exit -  halting vCPU - guest called HLT - ip=0xfff3
+vcpu 1 : XX. vm exit -  halting vCPU - guest called HLT - ip=0xff81
 vcpu 1 : XX. vm exit - reason 0xff handled by 'ep'
-vcpu 1 : XX. vm exit -  due to pause() request - ip=0xfff3
+vcpu 1 : XX. vm exit -  due to pause() request - ip=0xff81
 vcpu 1 : XX. vm exit - reason 0xff handled by 'ep'
-vcpu 1 : XX. vm exit -  due to pause() request - ip=0xfff5
+vcpu 1 : XX. vm exit -  due to pause() request - ip=0xff83
 vcpu 1 : XX. vm exit - reason 0x78 handled by 'ep'
-vcpu 1 : XX. vm exit -  halting vCPU - guest called HLT - ip=0xfff7
+vcpu 1 : XX. vm exit -  halting vCPU - guest called HLT - ip=0xff85
 vcpu 1 : XX. vm exit - reason 0xff handled by 'ep'
-vcpu 1 : XX. vm exit -  due to pause() request - ip=0xfff7
+vcpu 1 : XX. vm exit -  due to pause() request - ip=0xff85
 }
 
 puts $output_2
@@ -238,17 +238,17 @@ compare_output_to {
 [init -> vmm] vcpu 2 : created
 vcpu 2 : XX. vm exit - reason 0xfe handled by 'second ep'
 vcpu 2 : XX. vm exit - reason 0x78 handled by 'second ep'
-vcpu 2 : XX. vm exit -  halting vCPU - guest called HLT - ip=0xfff3
+vcpu 2 : XX. vm exit -  halting vCPU - guest called HLT - ip=0xff81
 vcpu 2 : XX. vm exit - reason 0xff handled by 'second ep'
-vcpu 2 : XX. vm exit -  due to pause() request - ip=0xfff3
+vcpu 2 : XX. vm exit -  due to pause() request - ip=0xff81
 vcpu 2 : XX. vm exit - reason 0x78 handled by 'second ep'
-vcpu 2 : XX. vm exit -  halting vCPU - guest called HLT - ip=0xfff3
+vcpu 2 : XX. vm exit -  halting vCPU - guest called HLT - ip=0xff81
 vcpu 2 : XX. vm exit - reason 0xff handled by 'second ep'
-vcpu 2 : XX. vm exit -  due to pause() request - ip=0xfff3
+vcpu 2 : XX. vm exit -  due to pause() request - ip=0xff81
 vcpu 2 : XX. vm exit - reason 0x78 handled by 'second ep'
-vcpu 2 : XX. vm exit -  halting vCPU - guest called HLT - ip=0xfff4
+vcpu 2 : XX. vm exit -  halting vCPU - guest called HLT - ip=0xff82
 vcpu 2 : XX. vm exit - reason 0xff handled by 'second ep'
-vcpu 2 : XX. vm exit -  due to pause() request - ip=0xfff4
+vcpu 2 : XX. vm exit -  due to pause() request - ip=0xff82
 }
 
 puts $output_3
@@ -257,7 +257,7 @@ compare_output_to {
 [init -> vmm] vcpu 3 : created
 vcpu 3 : XX. vm exit - reason 0xfe handled by 'second ep'
 vcpu 3 : XX. vm exit - reason 0x78 handled by 'second ep'
-vcpu 3 : XX. vm exit -  halting vCPU - guest called HLT - ip=0xfff3
+vcpu 3 : XX. vm exit -  halting vCPU - guest called HLT - ip=0xff81
 }
 
 set output $output_saved

repos/os/src/test/vmm_x86/component.cc

@@ -216,6 +216,9 @@ class Vmm::Vcpu
 };
 
 
+extern char _binary_guest_bin_start[];
+extern char _binary_guest_bin_end[];
+
 class Vmm::Vm
 {
 	private:
@@ -295,17 +298,9 @@ class Vmm::Vm
 
 			/* prepare guest memory with some instructions for testing */
 			uint8_t * guest = env.rm().attach(_memory);
-			unsigned byte = 0xff0;
 
-			guest[byte++] = 0x0f; /* rdtscp */
+			memcpy(guest, &_binary_guest_bin_start, 4096);
-			guest[byte++] = 0x01;
-			guest[byte++] = 0xf9;
 
-			guest[byte++] = 0xf4; /* HLT instruction */
-			guest[byte++] = 0xf4; /* HLT instruction */
-			guest[byte++] = 0xeb; /* JMP - endless loop to RIP */
-			guest[byte++] = 0xfe; /* JMP   of -2 byte (size of JMP inst) */
-			guest[byte++] = 0xf4; /* HLT instruction */
 			env.rm().detach(guest);
 
 			log ("let vCPUs run - first EP");

repos/os/src/test/vmm_x86/guest.s

@@ -0,0 +1,35 @@
+/*
+ * \brief  VM session interface test for x86: guest code
+ * \author Alexander Boettcher
+ * \author Christian Helmuth
+ * \date   2018-09-26
+ *
+ * The guest code is placed on the page hosting the reset vector 0xffff:fff0.
+ */
+
+/*
+ * Copyright (C) 2022 Genode Labs GmbH
+ *
+ * This file is part of the Genode OS framework, which is distributed
+ * under the terms of the GNU Affero General Public License version 3.
+ */
+
+.code16
+
+/* offset code start to keep the jmp distance in imm8 */
+.org 0xf7e, 0x90
+1:
+	rdtscp
+	hlt
+	hlt
+	jmp .
+	hlt
+
+	jmp .
+
+/* reset vector entry - just jmp to code start above */
+.org 0xff0, 0x90
+	jmp 1b
+
+/* fill page with hlt */
+.org 0x1000, 0xf4

repos/os/src/test/vmm_x86/target.mk

@@ -4,3 +4,13 @@ SRC_CC   = component.cc
 LIBS     = base
 
 CC_CXX_WARN_STRICT_CONVERSION =
+
+SRC_BIN = guest.bin
+
+guest.o: guest.s
+	$(MSG_ASSEM)$@
+	$(VERBOSE)$(CC) -m16 -c $< -o $@
+
+guest.bin: guest.o
+	$(MSG_CONVERT)$@
+	$(VERBOSE)$(OBJCOPY) -O binary $< $@