If code is loaded by EFI the loader will relocate the image
under 4GB. This cause offsets in x86 code generated by
sym_offs(SYMBOL) to be relocated too (basically they won't be
offsets from image base). In order to get real offset the
formulae "sym_offs(SYMBOL) - sym_offs(__image_base__)" is
used instead.
Also, in some case %esi register (that should point to
__image_base__ addresss) is not set so compute in all cases.
Code tested forcing failures in the code.
Signed-off-by: Frediano Ziglio <frediano.zig...@cloud.com>
---
xen/arch/x86/boot/head.S | 21 ++++++++++++++++++++-
1 file changed, 20 insertions(+), 1 deletion(-)
diff --git a/xen/arch/x86/boot/head.S b/xen/arch/x86/boot/head.S
index f027ff45fd..296f76146a 100644
--- a/xen/arch/x86/boot/head.S
+++ b/xen/arch/x86/boot/head.S
@@ -188,8 +188,27 @@ early_error: /* Here to improve the disassembly. */
xor %edi,%edi # No VGA text buffer
jmp .Lprint_err
.Lget_vtb:
- mov sym_esi(vga_text_buffer), %edi
+ mov $sym_offs(vga_text_buffer), %edi
.Lprint_err:
+ mov $sym_offs(__image_base__), %ebx
+
+ /* compute base, relocation or not */
+ call 1f
+1:
+ pop %esi
+ subl $sym_offs(1b), %esi
+ addl %ebx, %esi
+
+ /* adjust offset and load */
+ test %edi, %edi
+ jz 1f
+ subl %ebx, %edi
+ movl (%edi,%esi,1), %edi
+1:
+
+ /* adjust message offset */
+ subl %ebx, %ecx
+
add %ecx, %esi # Add string offset to relocation base.
# NOTE: No further use of sym_esi() till the end of the "function"!
1:
--
2.45.2
