linux-kernel - Re: [patch 2/2] x86_64: align RODATA kernel section to 2MB with CONFIG_DEBUG

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Message-ID: <20091015032429.GA10068@merkur.ravnborg.org>
Date:	Thu, 15 Oct 2009 05:24:29 +0200
From:	Sam Ravnborg <sam@...nborg.org>
To:	Suresh Siddha <suresh.b.siddha@...el.com>
Cc:	hpa@...or.com, mingo@...e.hu, tglx@...utronix.de,
	arjan@...ux.jf.intel.com, linux-kernel@...r.kernel.org,
	chinang.ma@...el.com
Subject: Re: [patch 2/2] x86_64: align RODATA kernel section to 2MB with
	CONFIG_DEBUG_RODATA

> Index: tree/arch/x86/include/asm/sections.h
> ===================================================================
> --- tree.orig/arch/x86/include/asm/sections.h
> +++ tree/arch/x86/include/asm/sections.h
> @@ -2,7 +2,13 @@
>  #define _ASM_X86_SECTIONS_H
>  
>  #include <asm-generic/sections.h>
> +#include <asm/uaccess.h>
>  
>  extern char __brk_base[], __brk_limit[];
> +extern struct exception_table_entry __stop___ex_table[];
> +
> +#if defined(CONFIG_X86_64) && defined(CONFIG_DEBUG_RODATA)
> +extern char __end_rodata_hpage_align[];
> +#endif
>  
>  #endif	/* _ASM_X86_SECTIONS_H */
> Index: tree/arch/x86/kernel/vmlinux.lds.S
> ===================================================================
> --- tree.orig/arch/x86/kernel/vmlinux.lds.S
> +++ tree/arch/x86/kernel/vmlinux.lds.S
> @@ -41,6 +41,21 @@ ENTRY(phys_startup_64)
>  jiffies_64 = jiffies;
>  #endif
>  
> +#if defined(CONFIG_X86_64) && defined(CONFIG_DEBUG_RODATA)
> +
> +#define X64_ALIGN_DEBUG_RODATA_BEGIN	. = ALIGN(HPAGE_SIZE);
> +
> +#define X64_ALIGN_DEBUG_RODATA_END				\
> +		. = ALIGN(HPAGE_SIZE);				\
> +		__end_rodata_hpage_align = .;
This symbol is only defined if CONFIG_DEBUG_RODATA is defined, but (see below).

> +
> +#else
> +
> +#define X64_ALIGN_DEBUG_RODATA_BEGIN
> +#define X64_ALIGN_DEBUG_RODATA_END
> +
> +#endif

A coment describing the purpose of
this would be nice.

> +
>  PHDRS {
>  	text PT_LOAD FLAGS(5);          /* R_E */
>  	data PT_LOAD FLAGS(7);          /* RWE */
> @@ -90,7 +105,9 @@ SECTIONS
>  
>  	EXCEPTION_TABLE(16) :text = 0x9090
>  
> +	X64_ALIGN_DEBUG_RODATA_BEGIN
>  	RO_DATA(PAGE_SIZE)
> +	X64_ALIGN_DEBUG_RODATA_END
>  
>  	/* Data */
>  	.data : AT(ADDR(.data) - LOAD_OFFSET) {
> Index: tree/arch/x86/mm/init_64.c
> ===================================================================
> --- tree.orig/arch/x86/mm/init_64.c
> +++ tree/arch/x86/mm/init_64.c
> @@ -726,9 +726,13 @@ void set_kernel_text_ro(void)
>  
>  void mark_rodata_ro(void)
>  {
> -	unsigned long start = PFN_ALIGN(_text), end = PFN_ALIGN(__end_rodata);
> +	unsigned long start = PFN_ALIGN(_text);
>  	unsigned long rodata_start =
>  		((unsigned long)__start_rodata + PAGE_SIZE - 1) & PAGE_MASK;
> +	unsigned long end = (unsigned long) &__end_rodata_hpage_align;
Here the symbol seems to be referenced unconditionally.

	Sam
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