[PATCH 02/42] x86, boot: Move compressed kernel to end of buffer before decompressing

[Yinghai Lu <yinghai@kernel.org>]

So we can find out ZO position easily during run-time for kasl buffer
searching.

Current code is using extract_offset to control copied kernel position, it
will put the copied kernel in the middle of buffer when kernel run size is
bigger than decompressed needed buffer size.

Current layout:
when init_size is the same as kernel run_size:
                                        run_size
0              extract_offset          init_size
|------------------|------------------------|
   VO text/data                   VO bss/brk
                   input ZO text ZO data

This patch try to:
move ZO to the end of buffer instead of middle of the buffer.
When init_size is bigger than kernel run size, will have

0                            run_size    init_size
|--------------------------------|----------|
   VO text/data        VO bss/brk
                       input ZO text ZO data

We already have init_size the buffer size, we can find the end easily
when copying ZO before decompressing.

Signed-off-by: Yinghai Lu <yinghai@kernel.org>
---
 arch/x86/boot/compressed/head_32.S     | 11 +++++++++--
 arch/x86/boot/compressed/head_64.S     |  8 ++++++--
 arch/x86/boot/compressed/mkpiggy.c     |  7 ++-----
 arch/x86/boot/compressed/vmlinux.lds.S |  1 +
 arch/x86/boot/header.S                 |  2 +-
 arch/x86/kernel/asm-offsets.c          |  1 +
 arch/x86/kernel/vmlinux.lds.S          |  1 +
 7 files changed, 21 insertions(+), 10 deletions(-)

diff --git a/arch/x86/boot/compressed/head_32.S b/arch/x86/boot/compressed/head_32.S
index 8ef964d..0c140f9 100644
--- a/arch/x86/boot/compressed/head_32.S
+++ b/arch/x86/boot/compressed/head_32.S
@@ -148,7 +148,9 @@ preferred_addr:
 1:
 
 	/* Target address to relocate to for decompression */
-	addl	$z_extract_offset, %ebx
+	movl    BP_init_size(%esi), %eax
+	subl    $_end, %eax
+	addl    %eax, %ebx
 
 	/* Set up the stack */
 	leal	boot_stack_end(%ebx), %esp
@@ -210,8 +212,13 @@ relocated:
 				/* push arguments for decompress_kernel: */
 	pushl	$z_run_size	/* size of kernel with .bss and .brk */
 	pushl	$z_output_len	/* decompressed length, end of relocs */
-	leal	z_extract_offset_negative(%ebx), %ebp
+
+	movl    BP_init_size(%esi), %eax
+	subl    $_end, %eax
+	movl    %ebx, %ebp
+	subl    %eax, %ebp
 	pushl	%ebp		/* output address */
+
 	pushl	$z_input_len	/* input_len */
 	leal	input_data(%ebx), %eax
 	pushl	%eax		/* input_data */
diff --git a/arch/x86/boot/compressed/head_64.S b/arch/x86/boot/compressed/head_64.S
index b0c0d16..67dd8d3 100644
--- a/arch/x86/boot/compressed/head_64.S
+++ b/arch/x86/boot/compressed/head_64.S
@@ -102,7 +102,9 @@ ENTRY(startup_32)
 1:
 
 	/* Target address to relocate to for decompression */
-	addl	$z_extract_offset, %ebx
+	movl	BP_init_size(%esi), %eax
+	subl	$_end, %eax
+	addl	%eax, %ebx
 
 /*
  * Prepare for entering 64 bit mode
@@ -330,7 +332,9 @@ preferred_addr:
 1:
 
 	/* Target address to relocate to for decompression */
-	leaq	z_extract_offset(%rbp), %rbx
+	movl	BP_init_size(%rsi), %ebx
+	subl	$_end, %ebx
+	addq	%rbp, %rbx
 
 	/* Set up the stack */
 	leaq	boot_stack_end(%rbx), %rsp
diff --git a/arch/x86/boot/compressed/mkpiggy.c b/arch/x86/boot/compressed/mkpiggy.c
index d8222f2..5faad09 100644
--- a/arch/x86/boot/compressed/mkpiggy.c
+++ b/arch/x86/boot/compressed/mkpiggy.c
@@ -83,11 +83,8 @@ int main(int argc, char *argv[])
 	printf("z_input_len = %lu\n", ilen);
 	printf(".globl z_output_len\n");
 	printf("z_output_len = %lu\n", (unsigned long)olen);
-	printf(".globl z_extract_offset\n");
-	printf("z_extract_offset = 0x%lx\n", offs);
-	/* z_extract_offset_negative allows simplification of head_32.S */
-	printf(".globl z_extract_offset_negative\n");
-	printf("z_extract_offset_negative = -0x%lx\n", offs);
+	printf(".globl z_min_extract_offset\n");
+	printf("z_min_extract_offset = 0x%lx\n", offs);
 	printf(".globl z_run_size\n");
 	printf("z_run_size = %lu\n", run_size);
 
diff --git a/arch/x86/boot/compressed/vmlinux.lds.S b/arch/x86/boot/compressed/vmlinux.lds.S
index 34d047c..e24e0a0 100644
--- a/arch/x86/boot/compressed/vmlinux.lds.S
+++ b/arch/x86/boot/compressed/vmlinux.lds.S
@@ -70,5 +70,6 @@ SECTIONS
 		_epgtable = . ;
 	}
 #endif
+	. = ALIGN(PAGE_SIZE);	/* keep ZO size page aligned */
 	_end = .;
 }
diff --git a/arch/x86/boot/header.S b/arch/x86/boot/header.S
index 16ef025..9bfab22 100644
--- a/arch/x86/boot/header.S
+++ b/arch/x86/boot/header.S
@@ -440,7 +440,7 @@ setup_data:		.quad 0			# 64-bit physical pointer to
 
 pref_address:		.quad LOAD_PHYSICAL_ADDR	# preferred load addr
 
-#define ZO_INIT_SIZE	(ZO__end - ZO_startup_32 + ZO_z_extract_offset)
+#define ZO_INIT_SIZE	(ZO__end - ZO_startup_32 + ZO_z_min_extract_offset)
 #define VO_INIT_SIZE	(VO__end - VO__text)
 #if ZO_INIT_SIZE > VO_INIT_SIZE
 #define INIT_SIZE ZO_INIT_SIZE
diff --git a/arch/x86/kernel/asm-offsets.c b/arch/x86/kernel/asm-offsets.c
index 8e3d22a1..d2e00bc 100644
--- a/arch/x86/kernel/asm-offsets.c
+++ b/arch/x86/kernel/asm-offsets.c
@@ -87,6 +87,7 @@ void common(void) {
 	OFFSET(BP_hardware_subarch, boot_params, hdr.hardware_subarch);
 	OFFSET(BP_version, boot_params, hdr.version);
 	OFFSET(BP_kernel_alignment, boot_params, hdr.kernel_alignment);
+	OFFSET(BP_init_size, boot_params, hdr.init_size);
 	OFFSET(BP_pref_address, boot_params, hdr.pref_address);
 	OFFSET(BP_code32_start, boot_params, hdr.code32_start);
 
diff --git a/arch/x86/kernel/vmlinux.lds.S b/arch/x86/kernel/vmlinux.lds.S
index 00bf300..5816920 100644
--- a/arch/x86/kernel/vmlinux.lds.S
+++ b/arch/x86/kernel/vmlinux.lds.S
@@ -325,6 +325,7 @@ SECTIONS
 		__brk_limit = .;
 	}
 
+	. = ALIGN(PAGE_SIZE);		/* keep VO_INIT_SIZE page aligned */
 	_end = .;
 
         STABS_DEBUG
-- 
1.8.4.5