x86: force suitable alignment in sources rather than in linker script

Besides being more logical this also allows verifying correct recording
of alignments in .o files.

The cpu0_stack related ASSERT() in xen.lds.S is now of questionable
value (as it now verifies correct tool chain behavior), but I've left
it in nevertheless.

Signed-off-by: Jan Beulich <jbeulich@xxxxxxxx>

--- a/xen/arch/x86/hvm/hvm.c
+++ b/xen/arch/x86/hvm/hvm.c
@@ -89,6 +89,7 @@ struct hvm_function_table hvm_funcs __re
  */
 #define HVM_IOBITMAP_SIZE (3 * PAGE_SIZE)
 unsigned long __section(".bss.page_aligned")
+    __attribute__((aligned(PAGE_SIZE)))
     hvm_io_bitmap[HVM_IOBITMAP_SIZE / BYTES_PER_LONG];
 
 /* Xen command-line option to enable HAP */
--- a/xen/arch/x86/mm.c
+++ b/xen/arch/x86/mm.c
@@ -125,7 +125,8 @@
 #include <asm/pci.h>
 
 /* Mapping of the fixmap space needed early. */
-l1_pgentry_t __section(".bss.page_aligned") l1_fixmap[L1_PAGETABLE_ENTRIES];
+l1_pgentry_t __section(".bss.page_aligned") __attribute__((aligned(PAGE_SIZE)))
+    l1_fixmap[L1_PAGETABLE_ENTRIES];
 
 #define MEM_LOG(_f, _a...) gdprintk(XENLOG_WARNING , _f "\n" , ## _a)
 
@@ -588,7 +589,8 @@ static inline void guest_get_eff_kern_l1
     TOGGLE_MODE();
 }
 
-const char __section(".bss.page_aligned.const") zero_page[PAGE_SIZE];
+const char __section(".bss.page_aligned.const")
+    __attribute__((aligned(PAGE_SIZE))) zero_page[PAGE_SIZE];
 
 static void invalidate_shadow_ldt(struct vcpu *v, int flush)
 {
--- a/xen/arch/x86/setup.c
+++ b/xen/arch/x86/setup.c
@@ -105,7 +105,8 @@ unsigned long __read_mostly xen_virt_end
 
 DEFINE_PER_CPU(struct tss_struct, init_tss);
 
-char __section(".bss.stack_aligned") cpu0_stack[STACK_SIZE];
+char __section(".bss.stack_aligned") __attribute__((aligned(STACK_SIZE)))
+    cpu0_stack[STACK_SIZE];
 
 struct cpuinfo_x86 __read_mostly boot_cpu_data = { 0, 0, 0, 0, -1 };
 
--- a/xen/arch/x86/xen.lds.S
+++ b/xen/arch/x86/xen.lds.S
@@ -222,7 +222,6 @@ SECTIONS
   } :text
 
   .data : {                    /* Data */
-       . = ALIGN(PAGE_SIZE);
        *(.data.page_aligned)
        *(.data)
        *(.data.rel)
@@ -231,10 +230,8 @@ SECTIONS
   } :text
 
   .bss : {                     /* BSS */
-       . = ALIGN(STACK_SIZE);
        __bss_start = .;
        *(.bss.stack_aligned)
-       . = ALIGN(PAGE_SIZE);
        *(.bss.page_aligned*)
        *(.bss)
        . = ALIGN(SMP_CACHE_BYTES);