efdcb4634a
With LinuxBoot Linux relied on the legacy method of fetching the RSDP pointer to get ACPI. This uses a more modern approach available since 2018 on the Linux kernel, which involves filling in the zero page. This method takes precedence over any other method of fetching the RSDP in Linux (UEFI, Kexec, Legacy/BIOS). Some UEFI zealots are threatening that legacy code will be removed from Linux so it's best to already adapt to that possibility. Tested on Qemu: - With qemu the RSDP is always in the EBDA, so checking if Linux uses the provided pointer is better done with a forced bad entry - With a fake bad pointer Linux correctly does not find RDSP Change-Id: I688b94608b03b0177c42d2834c7e3beb802ae686 Signed-off-by: Arthur Heymans <arthur@aheymans.xyz> Reviewed-on: https://review.coreboot.org/c/coreboot/+/62574 Tested-by: build bot (Jenkins) <no-reply@coreboot.org> Reviewed-by: Tim Wawrzynczak <twawrzynczak@chromium.org> Reviewed-by: Nico Huber <nico.h@gmx.de> Reviewed-by: Angel Pons <th3fanbus@gmail.com>
145 lines
3.2 KiB
ArmAsm
145 lines
3.2 KiB
ArmAsm
/* linux_trampoline */
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/* SPDX-License-Identifier: GPL-2.0-only */
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/* NOTE: THIS CODE MUST REMAIN POSITION INDEPENDENT
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* IT SHOULDN'T USE THE STACK
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* AND IN GENERAL EXPECT NOTHING BUT RAM TO WORK
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*/
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.code32
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.data
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#include "linux_trampoline.h"
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#define HEADER_SIG 0x4f49424c // LBIO little endian
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#define CB_TAG_FORWARD 0x11
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#define CB_TAG_MEMORY 0x1
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#define CB_TAG_FRAMEBUFFER 0x12
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#define CB_TAG_ACPI_RSDP 0x43
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#define ACPI_RSDP_ADDR 0x70
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#define E820_NR_OFFSET 0x1e8
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#define LINUX_ENTRY_OFFSET 0x214
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#define E820_OFFSET 0x2d0
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.trampoline_start:
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cld
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xor %edx, %edx
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mov $0, %ecx
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.headerSearch:
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mov $0x10000, %ebx
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add %ecx, %ebx
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mov (%ecx), %eax
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cmp $HEADER_SIG, %eax
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je .headerSearchDone // found the header
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add $16, %ecx
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cmp %ecx, %ebx
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jne .headerSearch
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.headerSearchDone:
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cmp %ecx, %ebx // reached the end == not found anything?
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je 2f // give up
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// we assume the checksum is okay, no test
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mov 4(%ecx), %ebx
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add %ecx, %ebx // ebx = cb_header + header_bytes
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mov 20(%ecx), %ecx // ecx = table_entries
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.tableScan:
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cmp $CB_TAG_FORWARD, (%ebx)
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jne .testMemory
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/* forward tag: assume 32bit pointer */
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mov 8(%ebx), %ecx
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jmp .headerSearch
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.testMemory:
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cmp $CB_TAG_MEMORY, (%ebx)
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jne .testAcpiRsdp
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/* memory tag: copy e820 map and entry count. also determine alt_mem_k */
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mov 4(%ebx), %eax
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sub $8, %eax
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shr $2, %eax /* eax = number of dwords of e820 data */
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cmp $(32 * 5), %eax /* linux wants at most 32 entries of 5 dwords */
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jng 1f
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mov $(32 * 5), %eax /* only copy 32 entries */
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1:
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mov %eax, %esi
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mov $5, %edi
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div %edi
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mov %eax, (LINUX_PARAM_LOC + E820_NR_OFFSET)
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mov %esi, %eax
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xchg %eax, %ecx
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lea 8(%ebx), %esi /* e820 data source */
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mov $(LINUX_PARAM_LOC + E820_OFFSET), %edi
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rep movsl
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xchg %eax, %ecx
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/* e820 and LB_TAG_MEMORY type don't fully match: remap unknown type to 2, reserved memory */
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mov (LINUX_PARAM_LOC + E820_NR_OFFSET), %eax
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mov $(LINUX_PARAM_LOC + E820_OFFSET), %edi
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.test_e820_entry:
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cmp $0, %eax
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je .endScan
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cmp $12, 16(%edi) /* type */
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jng .next_e820_entry
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/* Fixup the type to 2, reserved memory */
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mov $2, 16(%edi)
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.next_e820_entry:
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dec %eax
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add $20, %edi
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jmp .test_e820_entry
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.testAcpiRsdp:
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cmp $CB_TAG_ACPI_RSDP, (%ebx)
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jne .testFramebuffer
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mov 8(%ebx), %eax
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mov %eax, (LINUX_PARAM_LOC + ACPI_RSDP_ADDR)
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mov 12(%ebx), %eax
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mov %eax, (LINUX_PARAM_LOC + ACPI_RSDP_ADDR + 4)
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jmp .endScan
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.testFramebuffer:
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cmp $CB_TAG_FRAMEBUFFER, (%ebx)
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jne .endScan
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/* TODO: handle framebuffer tag */
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.endScan:
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add 4(%ebx), %ebx
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dec %ecx
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jnz .tableScan
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/* Setup basic code and data segment selectors for Linux
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**
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** Flat code segment descriptor:
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** selector: 0x10
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** base : 0x00000000
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** limit : 0xFFFFFFFF
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** type : code, execute, read
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**
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** Flat data segment descriptor:
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** selector: 0x18
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** base : 0x00000000
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** limit : 0xFFFFFFFF
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** type : data, read/write
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**
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** Use TRAMPOLINE_ENTRY_LOC as a scratchpad.
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*/
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mov $TRAMPOLINE_ENTRY_LOC, %eax
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movl $0x0000ffff, 16(%eax) // Set up the 2 new descriptors
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movl $0x00cf9b00, 20(%eax)
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movl $0x0000ffff, 24(%eax)
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movl $0x00cf9300, 28(%eax)
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movb $0x2b, 0(%eax) // Set the size
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movl %eax, 2(%eax) // Set pointer to new GDT
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lgdt (%eax) // Load it
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/* finally: jump to kernel */
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mov $LINUX_PARAM_LOC, %esi
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jmp *(LINUX_PARAM_LOC + LINUX_ENTRY_OFFSET)
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2:
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hlt
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jmp 2b
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.trampoline_end:
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