[arch][x86] fix multiboot to properly just cover the data segment, fix x86-64 bug

-Add -6 switch to do-qemux86 to build and run the x86-64 target
-Fix bug in x86-64 context switch, do not understand how it ever worked.

arch/x86-64/crt0.S

@@ -49,6 +49,7 @@ _start:
 
 .align 8
 
+.type multiboot_header,STT_OBJECT
 multiboot_header:
 	/* magic */
 	.int MULTIBOOT_HEADER_MAGIC
@@ -63,7 +64,7 @@ multiboot_header:
 	/* load_addr */
 	.int _start
 	/* load_end_addr */
-	.int __bss_start
+	.int __data_end
 	/* bss_end_addr */
 	.int __bss_end
 	/* entry_addr */

arch/x86-64/thread.c

@@ -118,8 +118,8 @@ void arch_context_switch(thread_t *oldthread, thread_t *newthread)
 		"pushq %%r14			\n\t"
 		"pushq %%r15			\n\t"
 
-		"movq %%rsp,%0			\n\t"
-		"movq %1,%%rsp			\n\t"
+		"movq %%rsp,%[old]			\n\t"
+		"movq %[new],%%rsp			\n\t"
 
 		"popq %%r15			\n\t"
 		"popq %%r14			\n\t"
@@ -140,9 +140,9 @@ void arch_context_switch(thread_t *oldthread, thread_t *newthread)
 
 		"ret				\n\t"
 		"1:				\n\t"
-		: "=g" (oldthread->arch.rsp)
-		: "g" (newthread->arch.rsp)
+		: [old] "=m" (oldthread->arch.rsp)
+		: [new] "g" (newthread->arch.rsp)
 	);
 }
 
-/* vim: noexpandtab */
+/* vim: noexpandtab: */

arch/x86/crt0.S

@@ -45,6 +45,7 @@ _start:
 
 .align 4
 
+.type multiboot_header,STT_OBJECT
 multiboot_header:
 	/* magic */
 	.int MULTIBOOT_HEADER_MAGIC
@@ -59,7 +60,7 @@ multiboot_header:
 	/* load_addr */
 	.int _start
 	/* load_end_addr */
-	.int __bss_start
+	.int __data_end
 	/* bss_end_addr */
 	.int __bss_end
 	/* entry_addr */

scripts/do-qemuarm

@@ -9,7 +9,7 @@ function HELP {
     echo "-t a virtio tap network device"
     echo "-d a virtio display"
     echo "-6 64bit arm"
-    echo "-M <memory in MB>"
+    echo "-m <memory in MB>"
     echo "-h for help"
     echo "all arguments after -- are passed to qemu directly"
     exit 1

scripts/do-qemux86

@@ -1,4 +1,43 @@
-#!/bin/sh
+#!/bin/bash
+
+function HELP {
+    echo "help:"
+    echo "-6 x86-64"
+    echo "-m <memory in MB>"
+    echo "-h for help"
+    echo "all arguments after -- are passed to qemu directly"
+    exit 1
+}
+
+DO_64BIT=0
+MEMSIZE=512
+SUDO=""
+MAKE_VARS=""
+
+while getopts bdhm:cMnt6 FLAG; do
+    case $FLAG in
+        6) DO_64BIT=1;;
+        m) MEMSIZE=$OPTARG;;
+        h) HELP;;
+        \?)
+            echo unrecognized option
+            HELP
+    esac
+done
+
+shift $((OPTIND-1))
+
+if [ $DO_64BIT == 1 ]; then
+    QEMU="qemu-system-x86_64"
+    PROJECT="pc-x86-64-test"
+else
+    QEMU="qemu-system-i386"
+    PROJECT="pc-x86-test"
+fi
+
+ARGS=" -m $MEMSIZE -kernel build-${PROJECT}/lk.elf -nographic"
+
+make $MAKE_VARS $PROJECT -j4 &&
+echo $SUDO $QEMU $ARGS $@ &&
+$SUDO $QEMU $ARGS $@
 
-make pc-x86-test -j4 &&
-qemu-system-i386 -kernel build-pc-x86-test/lk.elf -nographic $@