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x86, boot: straighten out ranges to copy/zero in compressed/head*.S

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Both on 32 and 64 bits, we copy all the way up to the end of bss,
except that on 64 bits there is a hack to avoid copying on top of the
page tables.  There is no point in copying bss at all, especially
since we are just about to zero it all anyway.

To clean up and unify the handling, we now do:

  - copy from startup_32 to _bss.
  - zero from _bss to _ebss.
  - the _ebss symbol is aligned to an 8-byte boundary.
  - the page tables are moved to a separate section.

Use _bss as the copy endpoint since _edata may be misaligned.

[ Impact: cleanup, trivial performance improvement ]

Signed-off-by: H. Peter Anvin <hpa@zytor.com>
This commit is contained in:
H. Peter Anvin 2009-05-08 16:20:34 -07:00
parent b40d68d5b5
commit 5b11f1cee5
3 changed files with 29 additions and 16 deletions
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8
arch/x86/boot/compressed/head_32.S
View file

@ -93,9 +93,9 @@ ENTRY(startup_32)
* where decompression in place becomes safe.
*/
pushl %esi
leal _ebss(%ebp), %esi
leal _ebss(%ebx), %edi
movl $(_ebss - startup_32), %ecx
leal _bss(%ebp), %esi
leal _bss(%ebx), %edi
movl $(_bss - startup_32), %ecx
std
rep movsb
cld
@ -125,7 +125,7 @@ relocated:
* Clear BSS
*/
xorl %eax, %eax
leal _edata(%ebx), %edi
leal _bss(%ebx), %edi
leal _ebss(%ebx), %ecx
subl %edi, %ecx
cld

18
arch/x86/boot/compressed/head_64.S
View file

@ -253,9 +253,9 @@ ENTRY(startup_64)
* Copy the compressed kernel to the end of our buffer
* where decompression in place becomes safe.
*/
leaq _end_before_pgt(%rip), %r8
leaq _end_before_pgt(%rbx), %r9
movq $_end_before_pgt /* - $startup_32 */, %rcx
leaq _bss(%rip), %r8
leaq _bss(%rbx), %r9
movq $_bss /* - $startup_32 */, %rcx
1: subq $8, %r8
subq $8, %r9
movq 0(%r8), %rax
@ -276,8 +276,8 @@ relocated:
* Clear BSS
*/
xorq %rax, %rax
leaq _edata(%rbx), %rdi
leaq _end_before_pgt(%rbx), %rcx
leaq _bss(%rbx), %rdi
leaq _ebss(%rbx), %rcx
subq %rdi, %rcx
cld
rep stosb
@ -329,3 +329,11 @@ boot_heap:
boot_stack:
.fill BOOT_STACK_SIZE, 1, 0
boot_stack_end:
/*
* Space for page tables (not in .bss so not zeroed)
*/
.section ".pgtable","a",@nobits
.balign 4096
pgtable:
.fill 6*4096, 1, 0

19
arch/x86/boot/compressed/vmlinux.lds.S
View file

@ -2,6 +2,8 @@ OUTPUT_FORMAT(CONFIG_OUTPUT_FORMAT, CONFIG_OUTPUT_FORMAT, CONFIG_OUTPUT_FORMAT)
#undef i386
#include <asm/page_types.h>
#ifdef CONFIG_X86_64
OUTPUT_ARCH(i386:x86-64)
ENTRY(startup_64)
@ -48,13 +50,16 @@ SECTIONS
*(.bss)
*(.bss.*)
*(COMMON)
#ifdef CONFIG_X86_64
. = ALIGN(8);
_end_before_pgt = . ;
. = ALIGN(4096);
pgtable = . ;
. = . + 4096 * 6;
#endif
. = ALIGN(8); /* For convenience during zeroing */
_ebss = .;
}
#ifdef CONFIG_X86_64
. = ALIGN(PAGE_SIZE);
.pgtable : {
_pgtable = . ;
*(.pgtable)
_epgtable = . ;
}
#endif
_end = .;
}