[coreboot-gerrit] Patch merged into coreboot/master: 3c12cb0 cbfstool:linux_trampoline: config CS and DS segment descriptors

the following patch was just integrated into master:
commit 3c12cb03847d2db41809ae434530782a7dbef48b
Author: Curt Brune 
Date:   Fri Aug 29 10:43:36 2014 -0700

cbfstool:linux_trampoline: config CS and DS segment descriptors

The Linux trampoline code does not set up the segment descriptors for
    __BOOT_CS and __BOOT_DS as described in the Linux kernel
    documentation:

... a GDT must be loaded with the descriptors for selectors
      __BOOT_CS(0x10) and __BOOT_DS(0x18); both descriptors must be 4G
      flat segment; __BOOT_CS must have execute/read permission, and
      __BOOT_DS must have read/write permission;

This is not a problem when launching a Linux payload from coreboot, as
    coreboot configures the segment descriptors at selectors 0x10 and
    0x18.  Coreboot configures these selectors in the ramstage to match
    what the Linux kernel expects (see
    coreboot/src/arch/x86/lib/c_start.S).

When the cbfs payload is launched in other environments, SeaBIOS for
    example, the segment descriptors are configured differently and the
    cbfs Linux payload does not work.

If the cbfs Linux payload is to be used in multiple environments
    should the trampoline needs to take care of the descriptors that Linux
    requires.

This patch updates the Linux trampoline code to configure the 4G flat
    descriptors that Linux expects.  The configuration is borrowed from
    the descriptor configs in coreboot/src/arch/x86/lib/c_start.S for
    selectors 0x10 and 0x18.

The linux_trampoline code is slightly refractored by defining the
    trampoline entry address, 0x40000, as TRAMPOLINE_ENTRY_LOC.  This
    definition is moved into a separate header file, linux_trampoline.h.
    This header file is now included by both the trampoline assembly
    language code and the trampoline loader C code.

The trampoline assembly language code can now use TRAMPOLINE_ENTRY_LOC
    as scratch space for the sgdt CPU instruction.

Testing Done:

Verified the Linux payload is booted correctly in the following
    environments:

1.  Coreboot -> Linux Payload

2.  Coreboot -> SeaBIOS -> Linux Payload: (previously did not work)

Change-Id: I888f74ff43073a6b7318f6713a8d4ecb804c0162
    Signed-off-by: Curt Brune 
    Reviewed-on: http://review.coreboot.org/6796
    Tested-by: build bot (Jenkins)
    Reviewed-by: Paul Menzel 
    Reviewed-by: Ronald G. Minnich

See http://review.coreboot.org/6796 for details.

-gerrit