[PATCH 02/14] x86, boot: honor CONFIG_PHYSICAL_START when relocatable

From: H. Peter Anvin
Date: Thu May 07 2009 - 18:27:58 EST

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From: H. Peter Anvin <hpa@xxxxxxxxx>

Currently, when building a relocatable kernel, CONFIG_PHYSICAL_START
is ignored. This is undesirable, as we would like to keep the kernel
out of ZONE_DMA and away from the possible memory hole at 15 MB (which
some vendors for some bizarre reason still have.)

With this patch, CONFIG_PHYSICAL_START is considered the *minimum*
address at which the kernel can be located; a relocating bootloader
can locate it higher, but not lower. This also restores the
originally intended behavior that CONFIG_RELOCATABLE is functionally a
noop if used with a non-relocating bootloader.

This patch also change movsb and stosb to movsl, stosl and stosq, to
shave a small fraction off the boot time.

Signed-off-by: H. Peter Anvin <hpa@xxxxxxxxx>
---
arch/x86/boot/compressed/head_32.S | 77 ++++++++++++++++++-----------------
arch/x86/boot/compressed/head_64.S | 37 ++++++++++-------
2 files changed, 61 insertions(+), 53 deletions(-)

diff --git a/arch/x86/boot/compressed/head_32.S b/arch/x86/boot/compressed/head_32.S
index 85bd328..31fc6dc 100644
--- a/arch/x86/boot/compressed/head_32.S
+++ b/arch/x86/boot/compressed/head_32.S
@@ -39,11 +39,11 @@ ENTRY(startup_32)

cli
movl $(__BOOT_DS),%eax
- movl %eax,%ds
- movl %eax,%es
- movl %eax,%fs
- movl %eax,%gs
- movl %eax,%ss
+ movl %eax, %ds
+ movl %eax, %es
+ movl %eax, %fs
+ movl %eax, %gs
+ movl %eax, %ss
1:

/* Calculate the delta between where we were compiled to run
@@ -64,12 +64,18 @@ ENTRY(startup_32)
*/

#ifdef CONFIG_RELOCATABLE
- movl %ebp, %ebx
- addl $(CONFIG_PHYSICAL_ALIGN - 1), %ebx
- andl $(~(CONFIG_PHYSICAL_ALIGN - 1)), %ebx
+ movl $LOAD_PHYSICAL_ADDR, %eax
+ movl %ebp, %ebx
+ cmpl %ebx, %eax
+ jbe 1f
+ movl %eax, %ebx
+1:
+ addl $(CONFIG_PHYSICAL_ALIGN - 1), %ebx
+ andl $(~(CONFIG_PHYSICAL_ALIGN - 1)), %ebx
#else
movl $LOAD_PHYSICAL_ADDR, %ebx
#endif
+ movl %ebx, %edi /* Save kernel target address */

/* Replace the compressed data size with the uncompressed size */
subl input_len(%ebp), %ebx
@@ -84,27 +90,30 @@ ENTRY(startup_32)
addl $4095, %ebx
andl $~4095, %ebx

-/* Copy the compressed kernel to the end of our buffer
+/*
+ * Set up the stack
+ */
+ leal boot_stack_end(%ebx), %esp
+ pushl %edi /* Saved kernel target address */
+
+/*
+ * Copy the compressed kernel to the end of our buffer
* where decompression in place becomes safe.
*/
pushl %esi
- leal _ebss(%ebp), %esi
- leal _ebss(%ebx), %edi
- movl $(_ebss - startup_32), %ecx
+ leal (_bss-4)(%ebp), %esi
+ leal (_bss-4)(%ebx), %edi
+ movl $(_bss - startup_32), %ecx
+ shrl $2, %ecx
std
- rep
- movsb
+ rep; movsl
cld
popl %esi

-/* Compute the kernel start address.
+/*
+ * %ebp -> kernel target address
*/
-#ifdef CONFIG_RELOCATABLE
- addl $(CONFIG_PHYSICAL_ALIGN - 1), %ebp
- andl $(~(CONFIG_PHYSICAL_ALIGN - 1)), %ebp
-#else
- movl $LOAD_PHYSICAL_ADDR, %ebp
-#endif
+ popl %ebp

/*
* Jump to the relocated address.
@@ -117,20 +126,14 @@ ENDPROC(startup_32)
relocated:

/*
- * Clear BSS
- */
- xorl %eax,%eax
- leal _edata(%ebx),%edi
- leal _ebss(%ebx), %ecx
- subl %edi,%ecx
- cld
- rep
- stosb
-
-/*
- * Setup the stack for the decompressor
+ * Clear BSS - note: stack is currently empty
*/
- leal boot_stack_end(%ebx), %esp
+ xorl %eax, %eax
+ leal _bss(%ebx), %edi
+ leal (_ebss+3)(%ebx), %ecx
+ subl %edi, %ecx
+ shrl $2, %ecx
+ rep; stosl

/*
* Do the decompression, and jump to the new kernel..
@@ -178,12 +181,12 @@ relocated:
/*
* Jump to the decompressed kernel.
*/
- xorl %ebx,%ebx
+ xorl %ebx, %ebx
jmp *%ebp

-.bss
/* Stack and heap for uncompression */
-.balign 4
+ .bss
+ .balign 4
boot_heap:
.fill BOOT_HEAP_SIZE, 1, 0
boot_stack:
diff --git a/arch/x86/boot/compressed/head_64.S b/arch/x86/boot/compressed/head_64.S
index ed4a829..f4ddd02 100644
--- a/arch/x86/boot/compressed/head_64.S
+++ b/arch/x86/boot/compressed/head_64.S
@@ -7,11 +7,6 @@
/*
* head.S contains the 32-bit startup code.
*
- * NOTE!!! Startup happens at absolute address 0x00001000, which is also where
- * the page directory will exist. The startup code will be overwritten by
- * the page directory. [According to comments etc elsewhere on a compressed
- * kernel it will end up at 0x1000 + 1Mb I hope so as I assume this. - AC]
- *
* Page 0 is deliberately kept safe, since System Management Mode code in
* laptops may need to access the BIOS data stored there. This is also
* useful for future device drivers that either access the BIOS via VM86
@@ -77,11 +72,17 @@ ENTRY(startup_32)
* contains the address where we should move the kernel image temporarily
* for safe in-place decompression.
*/
+ALIGN_MASK = (CONFIG_PHYSICAL_ALIGN-1) | (PMD_PAGE_SIZE-1)

#ifdef CONFIG_RELOCATABLE
+ movl $CONFIG_PHYSICAL_START, %eax
movl %ebp, %ebx
- addl $(PMD_PAGE_SIZE -1), %ebx
- andl $PMD_PAGE_MASK, %ebx
+ addl $ALIGN_MASK, %ebx
+ andl $~ALIGN_MASK, %ebx
+ cmpl %ebx, %eax
+ jbe 1f
+ movl %eax, %ebx
+1:
#else
movl $CONFIG_PHYSICAL_START, %ebx
#endif
@@ -221,13 +222,17 @@ ENTRY(startup_64)
/* Start with the delta to where the kernel will run at. */
#ifdef CONFIG_RELOCATABLE
leaq startup_32(%rip) /* - $startup_32 */, %rbp
- addq $(PMD_PAGE_SIZE - 1), %rbp
- andq $PMD_PAGE_MASK, %rbp
- movq %rbp, %rbx
+ movq $CONFIG_PHYSICAL_START, %rax
+ addq $ALIGN_MASK, %rbp
+ andq $~ALIGN_MASK, %rbp
+ cmpq %rbp, %rax
+ jbe 1f
+ movq %rax, %rbp
+1:
#else
movq $CONFIG_PHYSICAL_START, %rbp
- movq %rbp, %rbx
#endif
+ movq %rbp, %rbx

/* Replace the compressed data size with the uncompressed size */
movl input_len(%rip), %eax
@@ -266,13 +271,13 @@ relocated:
/*
* Clear BSS
*/
- xorq %rax, %rax
- leaq _edata(%rbx), %rdi
- leaq _end_before_pgt(%rbx), %rcx
+ xorl %eax, %eax
+ leaq _edata(%rip), %rdi
+ leaq _end_before_pgt(%rip), %rcx
subq %rdi, %rcx
+ shrq $3, %rcx
cld
- rep
- stosb
+ rep stosq

/* Setup the stack */
leaq boot_stack_end(%rip), %rsp
--
1.6.0.6

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Next message: H. Peter Anvin: "[PATCH 03/14] x86, config: change defaults PHYSICAL_START and PHYSICAL_ALIGN"
Previous message: H. Peter Anvin: "[PATCH 01/14] x86, boot: align the .bss section in the decompressor"
In reply to: H. Peter Anvin: "[PATCH 01/14] x86, boot: align the .bss section in the decompressor"
Next in thread: H. Peter Anvin: "[PATCH 03/14] x86, config: change defaults PHYSICAL_START and PHYSICAL_ALIGN"
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