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author | Stefan Reinauer <stefan.reinauer@coreboot.org> | 2015-11-20 17:58:59 +0100 |
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committer | Stefan Reinauer <stefan.reinauer@coreboot.org> | 2015-12-02 18:43:01 +0100 |
commit | 0316e1a69fa5d60f70afca00686d4b18a04e6dd2 (patch) | |
tree | aa074f350bf56cab1f2ff738937475183c83c4bf /util/cbfstool/linux_trampoline.S | |
parent | cbce4de97644e810251358fb212615a5b5244d42 (diff) | |
download | coreboot-0316e1a69fa5d60f70afca00686d4b18a04e6dd2.tar.gz coreboot-0316e1a69fa5d60f70afca00686d4b18a04e6dd2.tar.bz2 coreboot-0316e1a69fa5d60f70afca00686d4b18a04e6dd2.zip |
cbfstool: autocreate trampoline
Add the code necessary to create the linux trampoline blob.
Don't enforce this for the in-coreboot build or use objcopy
to produce linux_trampoline.o as it is a bit trickier to get
all the details right than I had hoped:
- you have to know the elf architecture of the host machine
- you might have to have more tools (xxd, perl, etc) installed
Change-Id: I9b7877c58d90f9fb21d16e0061a31e19fffa2470
Signed-off-by: Stefan Reinauer <stefan.reinauer@coreboot.org>
Reviewed-on: https://review.coreboot.org/12505
Tested-by: build bot (Jenkins)
Reviewed-by: Martin Roth <martinroth@google.com>
Diffstat (limited to 'util/cbfstool/linux_trampoline.S')
-rw-r--r-- | util/cbfstool/linux_trampoline.S | 133 |
1 files changed, 133 insertions, 0 deletions
diff --git a/util/cbfstool/linux_trampoline.S b/util/cbfstool/linux_trampoline.S new file mode 100644 index 000000000000..65819e948b2d --- /dev/null +++ b/util/cbfstool/linux_trampoline.S @@ -0,0 +1,133 @@ +/* + * linux_trampoline + * + * Copyright (C) 2013 Patrick Georgi <patrick@georgi-clan.de> + * + * This program is free software; you can redistribute it and/or modify + * it under the terms of the GNU General Public License as published by + * the Free Software Foundation; version 2 of the License. + * + * This program is distributed in the hope that it will be useful, + * but WITHOUT ANY WARRANTY; without even the implied warranty of + * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the + * GNU General Public License for more details. + */ + +/* NOTE: THIS CODE MUST REMAIN POSITION INDEPENDENT + * IT SHOULDN'T USE THE STACK + * AND IN GENERAL EXPECT NOTHING BUT RAM TO WORK + */ +.code32 +.data + +#include "linux_trampoline.h" +#define HEADER_SIG 0x4f49424c // LBIO little endian +#define CB_TAG_FORWARD 0x11 +#define CB_TAG_MEMORY 0x1 +#define CB_TAG_FRAMEBUFFER 0x12 + +#define E820_NR_OFFSET 0x1e8 +#define LINUX_ENTRY_OFFSET 0x214 +#define E820_OFFSET 0x2d0 + +.trampoline_start: + +cld +xor %edx, %edx +mov $0, %ecx + +.headerSearch: +mov $0x10000, %ebx +add %ecx, %ebx +mov (%ecx), %eax +cmp $HEADER_SIG, %eax +je .headerSearchDone // found the header +add $16, %ecx +cmp %ecx, %ebx +jne .headerSearch + +.headerSearchDone: +cmp %ecx, %ebx // reached the end == not found anything? +je 2f // give up + +// we assume the checksum is okay, no test +mov 4(%ecx), %ebx +add %ecx, %ebx // ebx = cb_header + header_bytes +mov 20(%ecx), %ecx // ecx = table_entries + +.tableScan: +cmp $CB_TAG_FORWARD, (%ebx) +jne .testMemory + +/* forward tag: assume 32bit pointer */ +mov 8(%ebx), %ecx +jmp .headerSearch + +.testMemory: +cmp $CB_TAG_MEMORY, (%ebx) +jne .testFramebuffer + +/* memory tag: copy e820 map and entry count. also determine alt_mem_k */ +mov 4(%ebx), %eax +sub $8, %eax +shr $2, %eax /* eax = number of dwords of e820 data */ +cmp $(32 * 5), %eax /* linux wants at most 32 entries of 5 dwords */ +jng 1f +mov $(32 * 5), %eax /* only copy 32 entries */ +1: +mov %eax, %esi +mov $5, %edi +div %edi +mov %eax, (LINUX_PARAM_LOC + E820_NR_OFFSET) +mov %esi, %eax +xchg %eax, %ecx +lea 8(%ebx), %esi /* e820 data source */ +mov $(LINUX_PARAM_LOC + E820_OFFSET), %edi +rep movsl +xchg %eax, %ecx +jmp .endScan + +.testFramebuffer: +cmp $CB_TAG_FRAMEBUFFER, (%ebx) +jne .endScan +/* TODO: handle framebuffer tag */ + +.endScan: +add 4(%ebx), %ebx +dec %ecx +jnz .tableScan + +/* Setup basic code and data segment selectors for Linux +** +** Flat code segment descriptor: +** selector: 0x10 +** base : 0x00000000 +** limit : 0xFFFFFFFF +** type : code, execute, read +** +** Flat data segment descriptor: +** selector: 0x18 +** base : 0x00000000 +** limit : 0xFFFFFFFF +** type : data, read/write +** +** 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) + +/* finally: jump to kernel */ +mov $LINUX_PARAM_LOC, %esi +jmp *(LINUX_PARAM_LOC + LINUX_ENTRY_OFFSET) + + +2: +hlt +jmp 2b + +.trampoline_end: |