ldso: Make truly self relocatable

On Linux the linker can now be loaded at arbitrary addresses, this became
necessary for newer kernel versions. The 'linux_arm' target is not supported.

Issue #1728

repos/base-linux/include/base/native_types.h

@@ -20,12 +20,14 @@
 
 /*
  * We cannot just include <semaphore.h> and <pthread.h> here
- * because this would impy the nested inclusion of a myriad
+ * because this would imply the nested inclusion of a myriad
  * of Linux types and would pollute the namespace for everyone
  * who includes this header file. We want to cleanly separate
  * Genode from POSIX.
  */
 
+extern Genode::addr_t _context_area_start;
+
 namespace Genode {
 
 	/**
@@ -129,10 +131,11 @@ namespace Genode {
 		 * Thread-context area configuration.
 		 *
 		 * Please update platform-specific files after changing these
-		 * values, e.g., 'base-linux/src/platform/context_area.*.ld'.
+		 * functions, e.g., 'base-linux/src/ld/context_area.*.ld'.
 		 */
-		static constexpr addr_t context_area_virtual_base() {
-			return 0x40000000UL; }
+		static addr_t context_area_virtual_base() {
+			return align_addr((addr_t)&_context_area_start, 20); }
+
 		static constexpr addr_t context_area_virtual_size() {
 			return 0x10000000UL; }
 

repos/base-linux/src/ld/context_area.nostdlib.ld

@@ -20,6 +20,9 @@ SECTIONS
 {
 	. = 0x40000000;
 	_context_area_start = .;
-	.context_area : { . += 0x10000000; } : context_area
-	_context_area_end = .;
+	/*
+	 * Since Linux loads ldso page aligned, we align the context area after
+	 * loading to a 1 MiB boundary, therefore we reserve one MiB more here.
+	 */
+	.context_area : { . += 0x10100000; } : context_area
 }

repos/base-linux/src/ld/context_area.stdlib.ld

@@ -16,5 +16,4 @@ SECTIONS
 	. = 0x40000000;
 	_context_area_start = .;
 	.context_area : { . += 0x10000000; }
-	_context_area_end = .;
 }

repos/base-linux/src/lib/lx_hybrid/lx_hybrid.cc

@@ -19,6 +19,12 @@
 
 extern "C" int raw_write_str(const char *str);
 
+/**
+ * Define context area
+ */
+Genode::addr_t _context_area_start;
+
+
 enum { verbose_atexit = false };