x86: cleanup boot-heap usage

The kernel decompressor wrapper uses memory located beyond the
end of the image. This might lead to hard to debug problems,
but even if it can be proven to be safe, it is at the very
least unclean. I don't see any advantages either, unless you
count it not being zeroed out as an advantage. This patch
moves the boot-heap area to the bss segment.

Signed-off-by: Alexander van Heukelum <heukelum@fastmail.fm>

Signed-off-by: Ingo Molnar <mingo@elte.hu>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>

arch/x86/boot/compressed/head_32.S

@@ -130,7 +130,7 @@ relocated:
 /*
  * Setup the stack for the decompressor
  */
-	leal stack_end(%ebx), %esp
+	leal boot_stack_end(%ebx), %esp
 
 /*
  * Do the decompression, and jump to the new kernel..
@@ -142,8 +142,8 @@ relocated:
 	pushl %eax	# input_len
 	leal input_data(%ebx), %eax
 	pushl %eax	# input_data
-	leal _end(%ebx), %eax
+	leal boot_heap(%ebx), %eax
-	pushl %eax	# end of the image as third argument
+	pushl %eax	# heap area as third argument
 	pushl %esi	# real mode pointer as second arg
 	call decompress_kernel
 	addl $20, %esp
@@ -181,7 +181,10 @@ relocated:
 	jmp *%ebp
 
 .bss
+/* Stack and heap for uncompression */
 .balign 4
-stack:
+boot_heap:
-	.fill 4096, 1, 0
+	.fill BOOT_HEAP_SIZE, 1, 0
-stack_end:
+boot_stack:
+	.fill BOOT_STACK_SIZE, 1, 0
+boot_stack_end:

arch/x86/boot/compressed/head_64.S

@@ -28,6 +28,7 @@
 #include <asm/segment.h>
 #include <asm/pgtable.h>
 #include <asm/page.h>
+#include <asm/boot.h>
 #include <asm/msr.h>
 #include <asm/asm-offsets.h>
 
@@ -62,7 +63,7 @@ startup_32:
 	subl	$1b, %ebp
 
 /* setup a stack and make sure cpu supports long mode. */
-	movl	$user_stack_end, %eax
+	movl	$boot_stack_end, %eax
 	addl	%ebp, %eax
 	movl	%eax, %esp
 
@@ -274,7 +275,7 @@ relocated:
 	stosb
 
 	/* Setup the stack */
-	leaq	user_stack_end(%rip), %rsp
+	leaq	boot_stack_end(%rip), %rsp
 
 	/* zero EFLAGS after setting rsp */
 	pushq	$0
@@ -285,7 +286,7 @@ relocated:
  */
 	pushq	%rsi			# Save the real mode argument
 	movq	%rsi, %rdi		# real mode address
-	leaq	_heap(%rip), %rsi	# _heap
+	leaq	boot_heap(%rip), %rsi	# malloc area for uncompression
 	leaq	input_data(%rip), %rdx  # input_data
 	movl	input_len(%rip), %eax
 	movq	%rax, %rcx		# input_len
@@ -310,9 +311,12 @@ gdt:
 	.quad	0x0080890000000000	/* TS descriptor */
 	.quad   0x0000000000000000	/* TS continued */
 gdt_end:
-	.bss
+
-/* Stack for uncompression */
+.bss
-	.balign 4
+/* Stack and heap for uncompression */
-user_stack:
+.balign 4
-	.fill 4096,4,0
+boot_heap:
-user_stack_end:
+	.fill BOOT_HEAP_SIZE, 1, 0
+boot_stack:
+	.fill BOOT_STACK_SIZE, 1, 0
+boot_stack_end:

arch/x86/boot/compressed/misc.c

@@ -217,12 +217,6 @@ static void putstr(const char *);
 static memptr free_mem_ptr;
 static memptr free_mem_end_ptr;
 
-#ifdef CONFIG_X86_64
-#define HEAP_SIZE             0x7000
-#else
-#define HEAP_SIZE             0x4000
-#endif
-
 static char *vidmem;
 static int vidport;
 static int lines, cols;
@@ -449,7 +443,7 @@ asmlinkage void decompress_kernel(void *rmode, memptr heap,
 
 	window = output;		/* Output buffer (Normally at 1M) */
 	free_mem_ptr     = heap;	/* Heap */
-	free_mem_end_ptr = heap + HEAP_SIZE;
+	free_mem_end_ptr = heap + BOOT_HEAP_SIZE;
 	inbuf  = input_data;		/* Input buffer */
 	insize = input_len;
 	inptr  = 0;

include/asm-x86/boot.h

@@ -17,4 +17,12 @@
 				+ (CONFIG_PHYSICAL_ALIGN - 1)) \
 				& ~(CONFIG_PHYSICAL_ALIGN - 1))
 
+#ifdef CONFIG_X86_64
+#define BOOT_HEAP_SIZE	0x7000
+#define BOOT_STACK_SIZE	0x4000
+#else
+#define BOOT_HEAP_SIZE	0x4000
+#define BOOT_STACK_SIZE	0x1000
+#endif
+
 #endif /* _ASM_BOOT_H */