Merge branch 'x86-urgent-for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip

Pull straggler x86 fixes from Peter Anvin:
 "Three groups of patches:

  - EFI boot stub documentation and the ability to print error messages;
  - Removal for PTRACE_ARCH_PRCTL for x32 (obsolete interface which
    should never have been ported, and the port is broken and
    potentially dangerous.)
  - ftrace stack corruption fixes.  I'm not super-happy about the
    technical implementation, but it is probably the least invasive in
    the short term.  In the future I would like a single method for
    nesting the debug stack, however."

* 'x86-urgent-for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip:
  x86, x32, ptrace: Remove PTRACE_ARCH_PRCTL for x32
  x86, efi: Add EFI boot stub documentation
  x86, efi; Add EFI boot stub console support
  x86, efi: Only close open files in error path
  ftrace/x86: Do not change stacks in DEBUG when calling lockdep
  x86: Allow nesting of the debug stack IDT setting
  x86: Reset the debug_stack update counter
  ftrace: Use breakpoint method to update ftrace caller
  ftrace: Synchronize variable setting with breakpoints

1 files changed, 65 insertions, 0 deletions

diff --git a/Documentation/x86/efi-stub.txt b/Documentation/x86/efi-stub.txt
new file mode 100644
index 000000000000..44e6bb6ead10
--- /dev/null
+++ b/Documentation/x86/efi-stub.txt
@@ -0,0 +1,65 @@
+                          The EFI Boot Stub
+                     ---------------------------
+
+On the x86 platform, a bzImage can masquerade as a PE/COFF image,
+thereby convincing EFI firmware loaders to load it as an EFI
+executable. The code that modifies the bzImage header, along with the
+EFI-specific entry point that the firmware loader jumps to are
+collectively known as the "EFI boot stub", and live in
+arch/x86/boot/header.S and arch/x86/boot/compressed/eboot.c,
+respectively.
+
+By using the EFI boot stub it's possible to boot a Linux kernel
+without the use of a conventional EFI boot loader, such as grub or
+elilo. Since the EFI boot stub performs the jobs of a boot loader, in
+a certain sense it *IS* the boot loader.
+
+The EFI boot stub is enabled with the CONFIG_EFI_STUB kernel option.
+
+
+**** How to install bzImage.efi
+
+The bzImage located in arch/x86/boot/bzImage must be copied to the EFI
+System Partiion (ESP) and renamed with the extension ".efi". Without
+the extension the EFI firmware loader will refuse to execute it. It's
+not possible to execute bzImage.efi from the usual Linux file systems
+because EFI firmware doesn't have support for them.
+
+
+**** Passing kernel parameters from the EFI shell
+
+Arguments to the kernel can be passed after bzImage.efi, e.g.
+
+        fs0:> bzImage.efi console=ttyS0 root=/dev/sda4
+
+
+**** The "initrd=" option
+
+Like most boot loaders, the EFI stub allows the user to specify
+multiple initrd files using the "initrd=" option. This is the only EFI
+stub-specific command line parameter, everything else is passed to the
+kernel when it boots.
+
+The path to the initrd file must be an absolute path from the
+beginning of the ESP, relative path names do not work. Also, the path
+is an EFI-style path and directory elements must be separated with
+backslashes (\). For example, given the following directory layout,
+
+fs0:>
+        Kernels\
+                        bzImage.efi
+                        initrd-large.img
+
+        Ramdisks\
+                        initrd-small.img
+                        initrd-medium.img
+
+to boot with the initrd-large.img file if the current working
+directory is fs0:\Kernels, the following command must be used,
+
+        fs0:\Kernels> bzImage.efi initrd=\Kernels\initrd-large.img
+
+Notice how bzImage.efi can be specified with a relative path. That's
+because the image we're executing is interpreted by the EFI shell,
+which understands relative paths, whereas the rest of the command line
+is passed to bzImage.efi.