| /* |
| * 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. |
| */ |
| |
| #if 0 |
| /* 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: |
| |
| .global trampoline_start, trampoline_size |
| trampoline_start: |
| .long .trampoline_start |
| trampoline_size: |
| .long .trampoline_end - .trampoline_start |
| #endif |
| |
| /* The code above is hand-crafted to fit various contraints. |
| * To simplify porting, the below matches the above. |
| * When changing any code in here, compile the above as a .S |
| * file, objcopy it to binary and paste the result below (minus |
| * the last 8 bytes which are trampoline_start and trampoline_size). |
| */ |
| const unsigned char trampoline[] = { |
| 0xfc, 0x31, 0xd2, 0xb9, 0x00, 0x00, 0x00, 0x00, 0xbb, 0x00, 0x00, 0x01, 0x00, 0x01, 0xcb, 0x8b, |
| 0x01, 0x3d, 0x4c, 0x42, 0x49, 0x4f, 0x74, 0x07, 0x83, 0xc1, 0x10, 0x39, 0xcb, 0x75, 0xe9, 0x39, |
| 0xcb, 0x0f, 0x84, 0x85, 0x00, 0x00, 0x00, 0x8b, 0x59, 0x04, 0x01, 0xcb, 0x8b, 0x49, 0x14, 0x83, |
| 0x3b, 0x11, 0x75, 0x05, 0x8b, 0x4b, 0x08, 0xeb, 0xcf, 0x83, 0x3b, 0x01, 0x75, 0x33, 0x8b, 0x43, |
| 0x04, 0x83, 0xe8, 0x08, 0xc1, 0xe8, 0x02, 0x3d, 0xa0, 0x00, 0x00, 0x00, 0x7e, 0x05, 0xb8, 0xa0, |
| 0x00, 0x00, 0x00, 0x89, 0xc6, 0xbf, 0x05, 0x00, 0x00, 0x00, 0xf7, 0xf7, 0xa3, 0xe8, 0x01, 0x09, |
| 0x00, 0x89, 0xf0, 0x91, 0x8d, 0x73, 0x08, 0xbf, 0xd0, 0x02, 0x09, 0x00, 0xf3, 0xa5, 0x91, 0xeb, |
| 0x05, 0x83, 0x3b, 0x12, 0x75, 0x00, 0x03, 0x5b, 0x04, 0x49, 0x75, 0xb3, 0xb8, 0x00, 0x00, 0x04, |
| 0x00, 0x0f, 0x01, 0x00, 0x8b, 0x58, 0x02, 0xc7, 0x43, 0x10, 0xff, 0xff, 0x00, 0x00, 0xc7, 0x43, |
| 0x14, 0x00, 0x9b, 0xcf, 0x00, 0xc7, 0x43, 0x18, 0xff, 0xff, 0x00, 0x00, 0xc7, 0x43, 0x1c, 0x00, |
| 0x93, 0xcf, 0x00, 0xbe, 0x00, 0x00, 0x09, 0x00, 0xff, 0x25, 0x14, 0x02, 0x09, 0x00, 0xf4, 0xeb, |
| 0xfd |
| }; |
| |
| const void * const trampoline_start = &trampoline; |
| const unsigned long trampoline_size = sizeof trampoline; |