From 7e748038cd7fcc7b54cf3133102073d5fe4cd0ce Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Roger=20Pau=20Monn=C3=A9?= <royger@FreeBSD.org>
Date: Fri, 26 Jun 2015 07:12:17 +0000
Subject: [PATCH] amd64: set the correct LMA values

The current linker script generates program headers with VMA == LMA:

Entry point 0xffffffff802e7000
There are 6 program headers, starting at offset 64

Program Headers:
  Type           Offset             VirtAddr           PhysAddr
                 FileSiz            MemSiz              Flags  Align
  PHDR           0x0000000000000040 0xffffffff80200040 0xffffffff80200040
                 0x0000000000000150 0x0000000000000150  R E    8
  INTERP         0x0000000000000190 0xffffffff80200190 0xffffffff80200190
                 0x000000000000000d 0x000000000000000d  R      1
      [Requesting program interpreter: /red/herring]
  LOAD           0x0000000000000000 0xffffffff80200000 0xffffffff80200000
                 0x00000000010559b0 0x00000000010559b0  R E    200000
  LOAD           0x0000000001056000 0xffffffff81456000 0xffffffff81456000
                 0x0000000000132638 0x000000000052ecf8  RW     200000
  DYNAMIC        0x0000000001056000 0xffffffff81456000 0xffffffff81456000
                 0x00000000000000d0 0x00000000000000d0  RW     8
  GNU_STACK      0x0000000000000000 0x0000000000000000 0x0000000000000000
                 0x0000000000000000 0x0000000000000000  RWE    8

This is fine for the FreeBSD loader, because it completely ignores p_paddr
and instead uses p_vaddr with a hardcoded offset. Other loaders however
acknowledge p_paddr (like the Xen ELF loader), in which case they will try
to load the kernel at the wrong place. Fix this by adding an AT keyword to
the first section specifying the physical address, other sections will
follow suit, so it ends up looking like:

Entry point 0xffffffff802e7000
There are 6 program headers, starting at offset 64

Program Headers:
  Type           Offset             VirtAddr           PhysAddr
                 FileSiz            MemSiz              Flags  Align
  PHDR           0x0000000000000040 0xffffffff80200040 0x0000000000200040
                 0x0000000000000150 0x0000000000000150  R E    8
  INTERP         0x0000000000000190 0xffffffff80200190 0x0000000000200190
                 0x000000000000000d 0x000000000000000d  R      1
      [Requesting program interpreter: /red/herring]
  LOAD           0x0000000000000000 0xffffffff80200000 0x0000000000200000
                 0x00000000010559b0 0x00000000010559b0  R E    200000
  LOAD           0x0000000001056000 0xffffffff81456000 0x0000000001456000
                 0x0000000000132638 0x000000000052ecf8  RW     200000
  DYNAMIC        0x0000000001056000 0xffffffff81456000 0x0000000001456000
                 0x00000000000000d0 0x00000000000000d0  RW     8
  GNU_STACK      0x0000000000000000 0x0000000000000000 0x0000000000000000
                 0x0000000000000000 0x0000000000000000  RWE    8

Tested on bare metal using the native FreeBSD loader and grub2 from TRUEOS.

Sponsored by: Citrix Systems R&D
Reviewed by: kib
Differential Revision: https://reviews.freebsd.org/D2783
---
 sys/amd64/amd64/xen-locore.S | 2 +-
 sys/conf/ldscript.amd64      | 7 ++++++-
 2 files changed, 7 insertions(+), 2 deletions(-)

diff --git a/sys/amd64/amd64/xen-locore.S b/sys/amd64/amd64/xen-locore.S
index da5f269685a7..43eb1f1fdb95 100644
--- a/sys/amd64/amd64/xen-locore.S
+++ b/sys/amd64/amd64/xen-locore.S
@@ -47,7 +47,7 @@
 	ELFNOTE(Xen, XEN_ELFNOTE_GUEST_VERSION,  .asciz, __XSTRING(__FreeBSD_version))
 	ELFNOTE(Xen, XEN_ELFNOTE_XEN_VERSION,    .asciz, "xen-3.0")
 	ELFNOTE(Xen, XEN_ELFNOTE_VIRT_BASE,      .quad,  KERNBASE)
-	ELFNOTE(Xen, XEN_ELFNOTE_PADDR_OFFSET,   .quad,  KERNBASE) /* Xen honours elf->p_paddr; compensate for this */
+	ELFNOTE(Xen, XEN_ELFNOTE_PADDR_OFFSET,   .quad,  0)
 	ELFNOTE(Xen, XEN_ELFNOTE_ENTRY,          .quad,  xen_start)
 	ELFNOTE(Xen, XEN_ELFNOTE_HYPERCALL_PAGE, .quad,	 hypercall_page)
 	ELFNOTE(Xen, XEN_ELFNOTE_HV_START_LOW,   .quad,  HYPERVISOR_VIRT_START)
diff --git a/sys/conf/ldscript.amd64 b/sys/conf/ldscript.amd64
index 9210a730c30e..a9521d83cfc0 100644
--- a/sys/conf/ldscript.amd64
+++ b/sys/conf/ldscript.amd64
@@ -8,7 +8,12 @@ SECTIONS
   /* Read-only sections, merged into text segment: */
   kernphys = CONSTANT (MAXPAGESIZE);
   . = kernbase + kernphys + SIZEOF_HEADERS;
-  .interp         : { *(.interp) }
+  /*
+   * Use the AT keyword in order to set the right LMA that contains
+   * the physical address where the section should be loaded. This is
+   * needed for the Xen loader which honours the LMA.
+   */
+  .interp         : AT (kernphys + SIZEOF_HEADERS) { *(.interp) }
   .hash           : { *(.hash) }
   .gnu.hash       : { *(.gnu.hash) }
   .dynsym         : { *(.dynsym) }