x86: decouple xen alignment setting from EFI/ELF build

Introduce a new Kconfig option to pick the alignment for xen binary.
To retain original behaviour, the default pick for EFI build is 2M and
ELF build 4K.

Make the PVHSHIM build use 2M alignment for potentially better
performance.

Signed-off-by: Wei Liu <wei.liu2@citrix.com>
Reviewed-by: Jan Beulich <jbeulich@suse.com>

xen/arch/x86/Kconfig

@@ -137,6 +137,29 @@ config TBOOT
 
 	  If unsure, say Y.
 
+choice
+	prompt "Alignment of Xen image"
+	default XEN_ALIGN_2M if PV_SHIM_EXCLUSIVE
+	default XEN_ALIGN_DEFAULT
+	---help---
+	  Specify alignment for Xen image.
+
+	  If unsure, choose "default".
+
+config XEN_ALIGN_DEFAULT
+	bool "Default alignment"
+	---help---
+	  Pick alignment according to build variants.
+
+	  For EFI build the default alignment is 2M. For ELF build
+	  the default alignment is 4K due to syslinux failing to handle
+	  the increment of image size induced by 2M alignment.
+
+config XEN_ALIGN_2M
+	bool "2M alignment"
+
+endchoice
+
 config XEN_GUEST
 	def_bool n
 	prompt "Xen Guest"

xen/arch/x86/xen.lds.S

@@ -12,7 +12,6 @@
 #define FORMAT "pei-x86-64"
 #undef __XEN_VIRT_START
 #define __XEN_VIRT_START __image_base__
-#define SECTION_ALIGN MB(2)
 #define DECL_SECTION(x) x :
 
 ENTRY(efi_start)
@@ -20,13 +19,18 @@ ENTRY(efi_start)
 #else /* !EFI */
 
 #define FORMAT "elf64-x86-64"
-#define SECTION_ALIGN PAGE_SIZE
 #define DECL_SECTION(x) x : AT(ADDR(x) - __XEN_VIRT_START)
 
 ENTRY(start_pa)
 
 #endif /* EFI */
 
+#if defined(CONFIG_XEN_ALIGN_2M) || defined(EFI)
+# define SECTION_ALIGN MB(2)
+#else
+# define SECTION_ALIGN PAGE_SIZE
+#endif
+
 OUTPUT_FORMAT(FORMAT, FORMAT, FORMAT)
 
 OUTPUT_ARCH(i386:x86-64)