x86: get rid of BOOT_TRAMPOLINE

We recently saw a machine that has the EBDA extending as low as
0x7c000, so that Xen fails to boot after relocating the trampoline.
To fix this, I removed BOOT_TRAMPOLINE and bootsym_phys completely.

Here are the parts:

1) the trampoline segment is set to 64k below the EBDA.  head.S grows
the ability to relocate the trampoline segment

2) reloc.c is made position-independent.  It allocates data below the
trampoline, whose address is passed in _eax.

3) cmdline.S is called before relocating, so all bootsym_phys there
become sym_phys.

Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>

jb: - fall back to low memory size (instead of segment 0x7c00) if EBDA
      value is out of range
    - also add upper limit check on EBDA value
    - fix and simplify inline assembly operands in reloc_mbi_struct()
    - use lret instead of retf
    - renamed early_stack to wakeup_stack, defined and used now only
      in wakeup.S
    - aligned reloc.bin's end of .text to 16 bytes, so that checking
      __bss_start == end works reliably

Signed-off-by: Jan Beulich <jbeulich@suse.com>

Committed-by: Keir Fraser <keir@xen.org>

1 files changed, 9 insertions, 6 deletions

diff --git a/xen/arch/x86/boot/trampoline.S b/xen/arch/x86/boot/trampoline.S
index dc4fd0603a..4421fc2c69 100644
--- a/xen/arch/x86/boot/trampoline.S
+++ b/xen/arch/x86/boot/trampoline.S
@@ -11,6 +11,13 @@
         .long 111b - (off) - .;            \
         .popsection
 
+#define bootsym_segrel(sym, off)           \
+        $0,$bootsym(sym);                  \
+111:;                                      \
+        .pushsection .trampoline_seg, "a"; \
+        .long 111b - (off) - .;            \
+        .popsection
+
         .globl trampoline_realmode_entry
 trampoline_realmode_entry:
         mov     %cs,%ax
@@ -151,14 +158,14 @@ trampoline_boot_cpu_entry:
 1:      mov     %eax,%cr0                 # CR0.PE = 0 (leave protected mode)
 
         /* Load proper real-mode values into %cs, %ds, %es and %ss. */
-        ljmp    $(BOOT_TRAMPOLINE>>4),$bootsym(1f)
+        ljmp    bootsym_segrel(1f,2)
 1:      mov     %cs,%ax
         mov     %ax,%ds
         mov     %ax,%es
         mov     %ax,%ss
 
         /* Initialise stack pointer and IDT, and enable irqs. */
-        mov     $bootsym(early_stack),%sp
+        xor     %sp,%sp
         lidt    bootsym(rm_idt)
         sti
 
@@ -220,7 +227,3 @@ rm_idt: .word   256*4-1, 0, 0
 #include "edd.S"
 #include "video.S"
 #include "wakeup.S"
-
-        .align  16
-        .fill   PAGE_SIZE,1,0
-early_stack: