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/*
* gbe/gbe.c
* This file is part of the ich9deblob utility from the libreboot project
*
* Copyright (C) 2014 Steve Shenton <sgsit@libreboot.org>
* Francis Rowe <info@gluglug.org.uk>
*
* 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, either version 3 of the License, or
* (at your option) any later version.
*
* 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.
*
* You should have received a copy of the GNU General Public License
* along with this program. If not, see <http://www.gnu.org/licenses/>.
*/
/*
* Provide gbe related functions.
*/
#include <stdio.h>
#include <string.h>
/* structs describing the data from gbe region */
#include "gbe.h"
/*
* ---------------------------------------------------------------------
* Gbe functions:
* ---------------------------------------------------------------------
*/
/* Read a 16-bit unsigned int from a supplied region buffer */
unsigned short gbeGetRegionWordFrom8kBuffer(int index, char* regionData)
{
return *((unsigned short*)(regionData + (index * 2)));
}
/*
* checksum calculation for 8k gbe region (algorithm based on datasheet)
* also works for 4k buffers, so long as isBackup remains false
*/
unsigned short gbeGetChecksumFrom8kBuffer(char* regionData, unsigned short desiredValue, int byteOffset)
{
int i;
/*
* byteOffset defines the byte address where the gbe begins in the buffer "regionData".
* However, this function works with 16-bit words. Shift the byte offset to the right for the word (16-bit) offset.
*/
int wordOffset = byteOffset >> 1;
unsigned short regionWord; /* store words here for adding to checksum */
unsigned short checksum = 0; /* this gbe's checksum */
for (i = 0; i < 0x3F; i++) {
regionWord = gbeGetRegionWordFrom8kBuffer(i+wordOffset, regionData);
checksum += regionWord;
}
checksum = desiredValue - checksum;
return checksum;
}
/* checksum calculation for 4k gbe struct (algorithm based on datasheet) */
unsigned short gbeGetChecksumFrom4kStruct(struct GBEREGIONRECORD_4K gbeStruct4k, unsigned short desiredValue)
{
char gbeBuffer4k[GBEREGIONSIZE_4K];
memcpy(&gbeBuffer4k, &gbeStruct4k, GBEREGIONSIZE_4K);
return gbeGetChecksumFrom8kBuffer(gbeBuffer4k, desiredValue, 0);
}
/* modify the gbe region extracted from a factory.rom dump */
struct GBEREGIONRECORD_8K deblobbedGbeStructFromFactory(struct GBEREGIONRECORD_8K factoryGbeStruct8k)
{
/*
* Correct the main gbe region. By default, the X200 (as shipped from Lenovo) comes
* with a broken main gbe region, where the backup gbe region is used instead. Modify
* it so that the main region is usable.
*/
struct GBEREGIONRECORD_8K deblobbedGbeStruct8k;
memcpy(&deblobbedGbeStruct8k, &factoryGbeStruct8k, GBEREGIONSIZE_8K);
deblobbedGbeStruct8k.backup.checkSum = gbeGetChecksumFrom4kStruct(deblobbedGbeStruct8k.backup, 0xBABA);
memcpy(&deblobbedGbeStruct8k.main, &deblobbedGbeStruct8k.backup, GBEREGIONSIZE_4K);
/*
* Debugging:
* calculate the 0x3F'th 16-bit uint to make the desired final checksum for GBe
* observed checksum matches (from X200 factory.rom dumps) on main: 0x3ABA 0x34BA 0x40BA. spec defined as 0xBABA.
* X200 ships with a broken main gbe region by default (invalid checksum, and more)
* The "backup" gbe regions on these machines are correct, though, and is what the machines default to
* For libreboot's purpose, we can do much better than that by fixing the main one... below is only debugging
*/
printf("\nfactory Gbe (main): calculated Gbe checksum: 0x%hx and actual GBe checksum: 0x%hx\n", gbeGetChecksumFrom4kStruct(factoryGbeStruct8k.main, 0xBABA), factoryGbeStruct8k.main.checkSum);
printf("factory Gbe (backup) calculated Gbe checksum: 0x%hx and actual GBe checksum: 0x%hx\n", gbeGetChecksumFrom4kStruct(factoryGbeStruct8k.backup, 0xBABA), factoryGbeStruct8k.backup.checkSum);
printf("\ndeblobbed Gbe (main): calculated Gbe checksum: 0x%hx and actual GBe checksum: 0x%hx\n", gbeGetChecksumFrom4kStruct(deblobbedGbeStruct8k.main, 0xBABA), deblobbedGbeStruct8k.main.checkSum);
printf("deblobbed Gbe (backup) calculated Gbe checksum: 0x%hx and actual GBe checksum: 0x%hx\n", gbeGetChecksumFrom4kStruct(deblobbedGbeStruct8k.backup, 0xBABA), deblobbedGbeStruct8k.backup.checkSum);
return deblobbedGbeStruct8k;
}
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