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7734a0f31e
After commit ce697ccee1 ("kbuild: remove head-y syntax"), I
started digging whether x86 is ready for removing this old cruft.
Removing its objects from the list makes the kernel unbootable.
This applies only to bzImage, vmlinux still works correctly.
The reason is that with no strict object order determined by the
linker arguments, not the linker script, startup_64 can be placed
not right at the beginning of the kernel.
Here's vmlinux.map's beginning before removing:
ffffffff81000000 vmlinux.o:(.head.text)
ffffffff81000000 startup_64
ffffffff81000070 secondary_startup_64
ffffffff81000075 secondary_startup_64_no_verify
ffffffff81000160 verify_cpu
and after:
ffffffff81000000 vmlinux.o:(.head.text)
ffffffff81000000 pvh_start_xen
ffffffff81000080 startup_64
ffffffff810000f0 secondary_startup_64
ffffffff810000f5 secondary_startup_64_no_verify
Not a problem itself, but the self-extractor code has the address of
that function hardcoded the beginning, not looking onto the ELF
header, which always contains the address of startup_{32,64}().
So, instead of doing an "act of blind faith", just take the address
from the ELF header and extract a relative offset to the entry
point. The decompressor function already returns a pointer to the
beginning of the kernel to the Asm code, which then jumps to it,
so add that offset to the return value.
This doesn't change anything for now, but allows to resign from the
"head object list" for x86 and makes sure valid Kbuild or any other
improvements won't break anything here in general.
Signed-off-by: Alexander Lobakin <alexandr.lobakin@intel.com>
Signed-off-by: Ingo Molnar <mingo@kernel.org>
Tested-by: Jiri Slaby <jirislaby@kernel.org>
Cc: "H. Peter Anvin" <hpa@zytor.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Link: https://lore.kernel.org/r/20230109170403.4117105-2-alexandr.lobakin@intel.com
221 lines
5.5 KiB
ArmAsm
221 lines
5.5 KiB
ArmAsm
/* SPDX-License-Identifier: GPL-2.0 */
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/*
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* linux/boot/head.S
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*
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* Copyright (C) 1991, 1992, 1993 Linus Torvalds
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*/
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/*
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* head.S contains the 32-bit startup code.
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*
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* NOTE!!! Startup happens at absolute address 0x00001000, which is also where
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* the page directory will exist. The startup code will be overwritten by
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* the page directory. [According to comments etc elsewhere on a compressed
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* kernel it will end up at 0x1000 + 1Mb I hope so as I assume this. - AC]
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*
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* Page 0 is deliberately kept safe, since System Management Mode code in
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* laptops may need to access the BIOS data stored there. This is also
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* useful for future device drivers that either access the BIOS via VM86
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* mode.
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*/
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/*
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* High loaded stuff by Hans Lermen & Werner Almesberger, Feb. 1996
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*/
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.text
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#include <linux/init.h>
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#include <linux/linkage.h>
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#include <asm/segment.h>
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#include <asm/page_types.h>
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#include <asm/boot.h>
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#include <asm/asm-offsets.h>
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#include <asm/bootparam.h>
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/*
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* These symbols needed to be marked as .hidden to prevent the BFD linker from
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* generating R_386_32 (rather than R_386_RELATIVE) relocations for them when
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* the 32-bit compressed kernel is linked as PIE. This is no longer necessary,
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* but it doesn't hurt to keep them .hidden.
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*/
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.hidden _bss
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.hidden _ebss
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.hidden _end
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__HEAD
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SYM_FUNC_START(startup_32)
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cld
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cli
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/*
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* Calculate the delta between where we were compiled to run
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* at and where we were actually loaded at. This can only be done
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* with a short local call on x86. Nothing else will tell us what
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* address we are running at. The reserved chunk of the real-mode
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* data at 0x1e4 (defined as a scratch field) are used as the stack
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* for this calculation. Only 4 bytes are needed.
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*/
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leal (BP_scratch+4)(%esi), %esp
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call 1f
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1: popl %edx
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addl $_GLOBAL_OFFSET_TABLE_+(.-1b), %edx
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/* Load new GDT */
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leal gdt@GOTOFF(%edx), %eax
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movl %eax, 2(%eax)
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lgdt (%eax)
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/* Load segment registers with our descriptors */
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movl $__BOOT_DS, %eax
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movl %eax, %ds
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movl %eax, %es
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movl %eax, %fs
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movl %eax, %gs
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movl %eax, %ss
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/*
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* %edx contains the address we are loaded at by the boot loader (plus the
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* offset to the GOT). The below code calculates %ebx to be the address where
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* we should move the kernel image temporarily for safe in-place decompression
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* (again, plus the offset to the GOT).
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*
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* %ebp is calculated to be the address that the kernel will be decompressed to.
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*/
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#ifdef CONFIG_RELOCATABLE
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leal startup_32@GOTOFF(%edx), %ebx
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#ifdef CONFIG_EFI_STUB
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/*
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* If we were loaded via the EFI LoadImage service, startup_32() will be at an
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* offset to the start of the space allocated for the image. efi_pe_entry() will
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* set up image_offset to tell us where the image actually starts, so that we
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* can use the full available buffer.
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* image_offset = startup_32 - image_base
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* Otherwise image_offset will be zero and has no effect on the calculations.
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*/
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subl image_offset@GOTOFF(%edx), %ebx
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#endif
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movl BP_kernel_alignment(%esi), %eax
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decl %eax
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addl %eax, %ebx
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notl %eax
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andl %eax, %ebx
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cmpl $LOAD_PHYSICAL_ADDR, %ebx
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jae 1f
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#endif
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movl $LOAD_PHYSICAL_ADDR, %ebx
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1:
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movl %ebx, %ebp // Save the output address for later
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/* Target address to relocate to for decompression */
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addl BP_init_size(%esi), %ebx
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subl $_end@GOTOFF, %ebx
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/* Set up the stack */
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leal boot_stack_end@GOTOFF(%ebx), %esp
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/* Zero EFLAGS */
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pushl $0
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popfl
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/*
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* Copy the compressed kernel to the end of our buffer
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* where decompression in place becomes safe.
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*/
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pushl %esi
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leal (_bss@GOTOFF-4)(%edx), %esi
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leal (_bss@GOTOFF-4)(%ebx), %edi
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movl $(_bss - startup_32), %ecx
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shrl $2, %ecx
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std
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rep movsl
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cld
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popl %esi
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/*
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* The GDT may get overwritten either during the copy we just did or
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* during extract_kernel below. To avoid any issues, repoint the GDTR
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* to the new copy of the GDT.
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*/
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leal gdt@GOTOFF(%ebx), %eax
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movl %eax, 2(%eax)
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lgdt (%eax)
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/*
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* Jump to the relocated address.
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*/
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leal .Lrelocated@GOTOFF(%ebx), %eax
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jmp *%eax
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SYM_FUNC_END(startup_32)
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#ifdef CONFIG_EFI_STUB
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SYM_FUNC_START(efi32_stub_entry)
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add $0x4, %esp
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movl 8(%esp), %esi /* save boot_params pointer */
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call efi_main
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/* efi_main returns the possibly relocated address of startup_32 */
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jmp *%eax
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SYM_FUNC_END(efi32_stub_entry)
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SYM_FUNC_ALIAS(efi_stub_entry, efi32_stub_entry)
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#endif
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.text
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SYM_FUNC_START_LOCAL_NOALIGN(.Lrelocated)
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/*
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* Clear BSS (stack is currently empty)
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*/
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xorl %eax, %eax
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leal _bss@GOTOFF(%ebx), %edi
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leal _ebss@GOTOFF(%ebx), %ecx
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subl %edi, %ecx
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shrl $2, %ecx
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rep stosl
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/*
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* Do the extraction, and jump to the new kernel..
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*/
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/* push arguments for extract_kernel: */
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pushl output_len@GOTOFF(%ebx) /* decompressed length, end of relocs */
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pushl %ebp /* output address */
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pushl input_len@GOTOFF(%ebx) /* input_len */
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leal input_data@GOTOFF(%ebx), %eax
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pushl %eax /* input_data */
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leal boot_heap@GOTOFF(%ebx), %eax
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pushl %eax /* heap area */
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pushl %esi /* real mode pointer */
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call extract_kernel /* returns kernel entry point in %eax */
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addl $24, %esp
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/*
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* Jump to the extracted kernel.
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*/
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xorl %ebx, %ebx
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jmp *%eax
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SYM_FUNC_END(.Lrelocated)
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.data
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.balign 8
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SYM_DATA_START_LOCAL(gdt)
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.word gdt_end - gdt - 1
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.long 0
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.word 0
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.quad 0x0000000000000000 /* Reserved */
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.quad 0x00cf9a000000ffff /* __KERNEL_CS */
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.quad 0x00cf92000000ffff /* __KERNEL_DS */
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SYM_DATA_END_LABEL(gdt, SYM_L_LOCAL, gdt_end)
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/*
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* Stack and heap for uncompression
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*/
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.bss
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.balign 4
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boot_heap:
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.fill BOOT_HEAP_SIZE, 1, 0
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boot_stack:
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.fill BOOT_STACK_SIZE, 1, 0
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boot_stack_end:
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