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https://github.com/AsahiLinux/u-boot
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03228b26d5
There are two blobs embedded into the u-boot image which are linked to run at an address which is different from where they actually end up in the ROM, one called "realmode" and one called "bios". There are realmode_setup and bios_setup functions which prepare those blobs by copying them into the location they're supposed to run from, among other things. During u-boot relocation from ROM to RAM, the text and a few data segments are copied over. The realmode and bios sections are not copied, and so the only place they can be read from is their original location in the ROM. Looking specifically at the bios blob, there are symbols defined in the linker script called __bios_start and __bios_size which are defined to be the start and size of the blob in the ROM. In the bios_setup function, there seem to be two mistakes happening. First, the offset from ROM to RAM is being added to __bios_start which implies that this code expects to use the copy moved to RAM. No such copy is made, so that's wrong. More subtly, when u-boot relocates itself, it goes through all of the relocations stored in .rel.dyn and fixes them up. This has the effect of transforming the __bios_start reference in bios_setup so that it refers to the version in RAM (if one existed) instead of the one in ROM. To correct for that, the offset actually needs to be subtracted out again to translate the address back into the ROM. The net effect is that for both blobs, a + needs to be changed to a -. Signed-off-by: Gabe Black <gabeblack@chromium.org>
96 lines
2.6 KiB
C
96 lines
2.6 KiB
C
/*
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* (C) Copyright 2002
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* Daniel Engström, Omicron Ceti AB, <daniel@omicron.se>
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*
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* See file CREDITS for list of people who contributed to this
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* project.
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*
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* This program is free software; you can redistribute it and/or
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* modify it under the terms of the GNU General Public License as
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* published by the Free Software Foundation; either version 2 of
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* the License, or (at your option) any later version.
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*
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* This program is distributed in the hope that it will be useful,
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* but WITHOUT ANY WARRANTY; without even the implied warranty of
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* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
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* GNU General Public License for more details.
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*
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* You should have received a copy of the GNU General Public License
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* along with this program; if not, write to the Free Software
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* Foundation, Inc., 59 Temple Place, Suite 330, Boston,
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* MA 02111-1307 USA
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*/
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#include <common.h>
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#include <asm/io.h>
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#include <asm/ptrace.h>
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#include <asm/realmode.h>
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#define REALMODE_MAILBOX ((char *)0xe00)
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int realmode_setup(void)
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{
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/*
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* The realmode section is not relocated and still in the ROM. The
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* __realmode_start symbol was adjusted, though, so adjust it back.
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*/
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ulong realmode_start = (ulong)&__realmode_start - gd->reloc_off;
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ulong realmode_size = (ulong)&__realmode_size;
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/* copy the realmode switch code */
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if (realmode_size > (REALMODE_MAILBOX - (char *)REALMODE_BASE)) {
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printf("realmode switch too large (%ld bytes, max is %d)\n",
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realmode_size,
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(int)(REALMODE_MAILBOX - (char *)REALMODE_BASE));
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return -1;
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}
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memcpy((char *)REALMODE_BASE, (void *)realmode_start, realmode_size);
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asm("wbinvd\n");
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return 0;
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}
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int enter_realmode(u16 seg, u16 off, struct pt_regs *in, struct pt_regs *out)
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{
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/* setup out thin bios emulation */
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if (bios_setup())
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return -1;
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if (realmode_setup())
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return -1;
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in->eip = off;
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in->xcs = seg;
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if ((in->esp & 0xffff) < 4)
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printf("Warning: entering realmode with sp < 4 will fail\n");
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memcpy(REALMODE_MAILBOX, in, sizeof(struct pt_regs));
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asm("wbinvd\n");
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__asm__ volatile (
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"lcall $0x20,%0\n" : : "i" (&realmode_enter));
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asm("wbinvd\n");
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memcpy(out, REALMODE_MAILBOX, sizeof(struct pt_regs));
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return out->eax;
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}
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/*
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* This code is supposed to access a realmode interrupt
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* it does currently not work for me
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*/
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int enter_realmode_int(u8 lvl, struct pt_regs *in, struct pt_regs *out)
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{
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/* place two instructions at 0x700 */
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writeb(0xcd, 0x700); /* int $lvl */
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writeb(lvl, 0x701);
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writeb(0xcb, 0x702); /* lret */
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asm("wbinvd\n");
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enter_realmode(0x00, 0x700, in, out);
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return out->eflags & 0x00000001;
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}
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