From eeb83b6b53fc72fda60dea31fc7e0cf155ccdecf Mon Sep 17 00:00:00 2001 From: "Ronald G. Minnich" Date: Wed, 18 Jul 2018 07:19:30 -0700 Subject: linux_trampoline: use trampoline RAM for the GDT The linux trampoline was modifying the existing GDT to add the 0x10 and 0x18 descriptors for Linux. This will not work when the existing GDT is in ROM. Change the code to set up a new GDT in what we know to be RAM. Tested by booting a linux payload. The main reason this works is that Linux almost immediately loads its own GDT and then segment registers. This GDT is a very temporary bridge. Note that none of this change used to be necessary; the coreboot GDT was originally compatible with Linux (ca 2000); then Linux changed. Change-Id: I13990052fbfd6a500adab8a2db8f7aead1d24fa6 Signed-off-by: Ronald G. Minnich Reviewed-on: https://review.coreboot.org/27529 Tested-by: build bot (Jenkins) Reviewed-by: Patrick Georgi --- util/cbfstool/linux_trampoline.S | 15 +++++++-------- 1 file changed, 7 insertions(+), 8 deletions(-) (limited to 'util/cbfstool/linux_trampoline.S') diff --git a/util/cbfstool/linux_trampoline.S b/util/cbfstool/linux_trampoline.S index 65819e948b..3b4e730b33 100644 --- a/util/cbfstool/linux_trampoline.S +++ b/util/cbfstool/linux_trampoline.S @@ -31,7 +31,6 @@ #define E820_OFFSET 0x2d0 .trampoline_start: - cld xor %edx, %edx mov $0, %ecx @@ -114,12 +113,13 @@ jnz .tableScan ** Use TRAMPOLINE_ENTRY_LOC as a scratchpad. */ mov $TRAMPOLINE_ENTRY_LOC, %eax -sgdt (%eax) -mov 2(%eax), %ebx -movl $0x0000ffff, 16(%ebx) -movl $0x00cf9b00, 20(%ebx) -movl $0x0000ffff, 24(%ebx) -movl $0x00cf9300, 28(%ebx) +movl $0x0000ffff, 16(%eax) // Set up the 2 new descriptors +movl $0x00cf9b00, 20(%eax) +movl $0x0000ffff, 24(%eax) +movl $0x00cf9300, 28(%eax) +movb $0x2b, 0(%eax) // Set the size +movl %eax, 2(%eax) // Set pointer to new GDT +lgdt (%eax) // Load it /* finally: jump to kernel */ mov $LINUX_PARAM_LOC, %esi @@ -129,5 +129,4 @@ jmp *(LINUX_PARAM_LOC + LINUX_ENTRY_OFFSET) 2: hlt jmp 2b - .trampoline_end: -- cgit v1.2.3