Re: [RFC PATCH 7/8] ARM: vmlinux.lds: Setup physical load address not virtual

From: Nicolas Pitre <nicolas.pitre@linaro.org>
To: Michal Simek <monstr@monstr.eu>
Cc: linux-kernel@vger.kernel.org,
	Russell King <linux@arm.linux.org.uk>,
	Marc Zyngier <marc.zyngier@arm.com>,
	Grant Likely <grant.likely@secretlab.ca>,
	Will Deacon <will.deacon@arm.com>,
	Rob Herring <rob.herring@calxeda.com>,
	linux-arm-kernel@lists.infradead.org,
	Ohad Ben-Cohen <ohad@wizery.com>,
	Peter Crosthwaite <peter.crosthwaite@petalogix.com>
Subject: Re: [RFC PATCH 7/8] ARM: vmlinux.lds:  Setup physical load address not virtual
Date: Mon, 18 Jun 2012 10:06:36 -0400 (EDT)	[thread overview]
Message-ID: <alpine.LFD.2.02.1206181000540.23555@xanadu.home> (raw)
In-Reply-To: <1340019011-18642-8-git-send-email-monstr@monstr.eu>

On Mon, 18 Jun 2012, Michal Simek wrote:

> Setup correct virtual and physical address in ELF LOAD section.

We are moving to a single kernel binary for multiple targets, including 
targets with different physical load addresses.  The kernel code figures 
out at run time what the actual physical address is when 
CONFIG_ARM_PATCH_PHYS_VIRT is set which is the default these days.  In 
other words, we don't know the physical offset at build time in that 
case and CONFIG_PHYS_OFFSET is simply not defined.

Why do you need this change?  Your patch comments are lacking 
justification for them.

> Signed-off-by: Michal Simek <monstr@monstr.eu>
> ---
>  arch/arm/include/asm/page.h   |    2 ++
>  arch/arm/kernel/vmlinux.lds.S |   28 ++++++++++++++--------------
>  2 files changed, 16 insertions(+), 14 deletions(-)
> 
> diff --git a/arch/arm/include/asm/page.h b/arch/arm/include/asm/page.h
> index ecf9019..4070209 100644
> --- a/arch/arm/include/asm/page.h
> +++ b/arch/arm/include/asm/page.h
> @@ -15,6 +15,8 @@
>  #define PAGE_SIZE		(_AC(1,UL) << PAGE_SHIFT)
>  #define PAGE_MASK		(~(PAGE_SIZE-1))
>  
> +#define LOAD_OFFSET	(CONFIG_PAGE_OFFSET - CONFIG_PHYS_OFFSET)
> +
>  #ifndef __ASSEMBLY__
>  
>  #ifndef CONFIG_MMU
> diff --git a/arch/arm/kernel/vmlinux.lds.S b/arch/arm/kernel/vmlinux.lds.S
> index c887be0..b996bc0 100644
> --- a/arch/arm/kernel/vmlinux.lds.S
> +++ b/arch/arm/kernel/vmlinux.lds.S
> @@ -3,11 +3,11 @@
>   * Written by Martin Mares <mj@atrey.karlin.mff.cuni.cz>
>   */
>  
> +#include <asm/page.h>
>  #include <asm-generic/vmlinux.lds.h>
>  #include <asm/cache.h>
>  #include <asm/thread_info.h>
>  #include <asm/memory.h>
> -#include <asm/page.h>
>  	
>  #define PROC_INFO							\
>  	. = ALIGN(4);							\
> @@ -86,11 +86,11 @@ SECTIONS
>  #else
>  	. = PAGE_OFFSET + TEXT_OFFSET;
>  #endif
> -	.head.text : {
> +	.head.text : AT(ADDR(.head.text) - LOAD_OFFSET) {
>  		_text = .;
>  		HEAD_TEXT
>  	}
> -	.text : {			/* Real text segment		*/
> +	.text : AT(ADDR(.text) - LOAD_OFFSET){	/* Real text segment	*/
>  		_stext = .;		/* Text and read-only data	*/
>  			__exception_text_start = .;
>  			*(.exception.text)
> @@ -132,12 +132,12 @@ SECTIONS
>  	 * Stack unwinding tables
>  	 */
>  	. = ALIGN(8);
> -	.ARM.unwind_idx : {
> +	.ARM.unwind_idx : AT(ADDR(.ARM.unwind_idx) - LOAD_OFFSET) {
>  		__start_unwind_idx = .;
>  		*(.ARM.exidx*)
>  		__stop_unwind_idx = .;
>  	}
> -	.ARM.unwind_tab : {
> +	.ARM.unwind_tab : AT(ADDR(.ARM.unwind_tab) - LOAD_OFFSET) {
>  		__start_unwind_tab = .;
>  		*(.ARM.extab*)
>  		__stop_unwind_tab = .;
> @@ -152,35 +152,35 @@ SECTIONS
>  #endif
>  
>  	INIT_TEXT_SECTION(8)
> -	.exit.text : {
> +	.exit.text : AT(ADDR(.exit.text) - LOAD_OFFSET) {
>  		ARM_EXIT_KEEP(EXIT_TEXT)
>  	}
> -	.init.proc.info : {
> +	.init.proc.info : AT(ADDR(.init.proc.info) - LOAD_OFFSET) {
>  		ARM_CPU_DISCARD(PROC_INFO)
>  	}
> -	.init.arch.info : {
> +	.init.arch.info : AT(ADDR(.init.arch.info) - LOAD_OFFSET) {
>  		__arch_info_begin = .;
>  		*(.arch.info.init)
>  		__arch_info_end = .;
>  	}
> -	.init.tagtable : {
> +	.init.tagtable : AT(ADDR(.init.tagtable) - LOAD_OFFSET) {
>  		__tagtable_begin = .;
>  		*(.taglist.init)
>  		__tagtable_end = .;
>  	}
>  #ifdef CONFIG_SMP_ON_UP
> -	.init.smpalt : {
> +	.init.smpalt : AT(ADDR(.init.smpalt) - LOAD_OFFSET) {
>  		__smpalt_begin = .;
>  		*(.alt.smp.init)
>  		__smpalt_end = .;
>  	}
>  #endif
> -	.init.pv_table : {
> +	.init.pv_table : AT(ADDR(.init.pv_table) - LOAD_OFFSET) {
>  		__pv_table_begin = .;
>  		*(.pv_table)
>  		__pv_table_end = .;
>  	}
> -	.init.data : {
> +	.init.data : AT(ADDR(.init.data) - LOAD_OFFSET) {
>  #ifndef CONFIG_XIP_KERNEL
>  		INIT_DATA
>  #endif
> @@ -191,7 +191,7 @@ SECTIONS
>  		INIT_RAM_FS
>  	}
>  #ifndef CONFIG_XIP_KERNEL
> -	.exit.data : {
> +	.exit.data : AT(ADDR(.exit.data) - LOAD_OFFSET) {
>  		ARM_EXIT_KEEP(EXIT_DATA)
>  	}
>  #endif
> @@ -207,7 +207,7 @@ SECTIONS
>  	__data_loc = .;
>  #endif
>  
> -	.data : AT(__data_loc) {
> +	.data : AT(ADDR(.data) - LOAD_OFFSET) {
>  		_data = .;		/* address in memory */
>  		_sdata = .;
>  
> -- 
> 1.7.0.4
> 