linux-kernel - Re: [PATCH] arm: remove dead blocks in XIP

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Date:	Thu, 24 Mar 2016 20:48:13 +0100
From:	Arnd Bergmann <arnd@...db.de>
To:	linux-arm-kernel@...ts.infradead.org
Cc:	Jonas Rabenstein <jonas.rabenstein@...dium.uni-erlangen.de>,
	linux-kernel@...r.kernel.org, linux@....linux.org.uk,
	ard.biesheuvel@...aro.org
Subject: Re: [PATCH] arm: remove dead blocks in XIP_KERNEL link script

On Thursday 24 March 2016 19:58:40 Jonas Rabenstein wrote:
> Commit 538bf4694898 ("ARM: 8513/1: xip: Move XIP linking to a separate
> file") separated all CONFIG_XIP_KERNEL related portions of the linker
> script into a separate file. The copied parts depending on CONFIG_SMP
> may be removed, as CONFIG_SMP (and related options) can never be
> selected together with CONFIG_XIP_KERNEL. CONFIG_SMP_ON_UP has a direct
> dependency on !CONFIG_XIP_KERNEL. CONFIG_XIP_KERNEL itself depends on
> !ARCH_MULTIPLATFORM, but all devices specifying HAVE_SMP are also some
> kind of multiplatform devices. Finally, HAVE_TCM is also only selected
> by multiplatform devices and may not selected for the same reasons.
> 
> Signed-off-by: Jonas Rabenstein <jonas.rabenstein@...dium.uni-erlangen.de>
> ---
>  I detected the issue with chimaera, a tool I currently develop for my bachelor
>  thesis extending the undertaker tool suite (https://undertaker.cs.fau.de).

Your analysis of the existing dependencies sounds correct to me. We clearly
cannot have SMP_ON_UP, and it may make sense to drop the TCM section
as it is very unlikely to get used here (it's already basically unused
on the non-XIP kernel, but should remain there).

Regarding SMP and HOTPLUG_CPU, I think it makes sense to leave the support
in this file, because it's possible that we will need that in the foreseeable
future.

	Arnd

>  arch/arm/kernel/vmlinux-xip.lds.S | 75 ---------------------------------------
>  1 file changed, 75 deletions(-)
> 
> diff --git a/arch/arm/kernel/vmlinux-xip.lds.S b/arch/arm/kernel/vmlinux-xip.lds.S
> index cba1ec8..7da95f8 100644
> --- a/arch/arm/kernel/vmlinux-xip.lds.S
> +++ b/arch/arm/kernel/vmlinux-xip.lds.S
> @@ -25,13 +25,8 @@
>  	*(.hyp.idmap.text)						\
>  	VMLINUX_SYMBOL(__hyp_idmap_text_end) = .;
>  
> -#ifdef CONFIG_HOTPLUG_CPU
> -#define ARM_CPU_DISCARD(x)
> -#define ARM_CPU_KEEP(x)		x
> -#else
>  #define ARM_CPU_DISCARD(x)	x
>  #define ARM_CPU_KEEP(x)
> -#endif
>  
>  #if (defined(CONFIG_SMP_ON_UP) && !defined(CONFIG_DEBUG_SPINLOCK)) || \
>  	defined(CONFIG_GENERIC_BUG)
> @@ -74,9 +69,7 @@ SECTIONS
>  		*(.text.fixup)
>  		*(__ex_table)
>  #endif
> -#ifndef CONFIG_SMP_ON_UP
>  		*(.alt.smp.init)
> -#endif
>  		*(.discard)
>  		*(.discard.*)
>  	}
> @@ -177,13 +170,6 @@ SECTIONS
>  		*(.taglist.init)
>  		__tagtable_end = .;
>  	}
> -#ifdef CONFIG_SMP_ON_UP
> -	.init.smpalt : {
> -		__smpalt_begin = .;
> -		*(.alt.smp.init)
> -		__smpalt_end = .;
> -	}
> -#endif
>  	.init.pv_table : {
>  		__pv_table_begin = .;
>  		*(.pv_table)
> @@ -197,10 +183,6 @@ SECTIONS
>  		INIT_RAM_FS
>  	}
>  
> -#ifdef CONFIG_SMP
> -	PERCPU_SECTION(L1_CACHE_BYTES)
> -#endif
> -
>  	_exiprom = .;			/* End of XIP ROM area */
>  	__data_loc = ALIGN(4);		/* location in binary */
>  	. = PAGE_OFFSET + TEXT_OFFSET;
> @@ -236,63 +218,6 @@ SECTIONS
>  	}
>  	_edata_loc = __data_loc + SIZEOF(.data);
>  
> -#ifdef CONFIG_HAVE_TCM
> -        /*
> -	 * We align everything to a page boundary so we can
> -	 * free it after init has commenced and TCM contents have
> -	 * been copied to its destination.
> -	 */
> -	.tcm_start : {
> -		. = ALIGN(PAGE_SIZE);
> -		__tcm_start = .;
> -		__itcm_start = .;
> -	}
> -
> -	/*
> -	 * Link these to the ITCM RAM
> -	 * Put VMA to the TCM address and LMA to the common RAM
> -	 * and we'll upload the contents from RAM to TCM and free
> -	 * the used RAM after that.
> -	 */
> -	.text_itcm ITCM_OFFSET : AT(__itcm_start)
> -	{
> -		__sitcm_text = .;
> -		*(.tcm.text)
> -		*(.tcm.rodata)
> -		. = ALIGN(4);
> -		__eitcm_text = .;
> -	}
> -
> -	/*
> -	 * Reset the dot pointer, this is needed to create the
> -	 * relative __dtcm_start below (to be used as extern in code).
> -	 */
> -	. = ADDR(.tcm_start) + SIZEOF(.tcm_start) + SIZEOF(.text_itcm);
> -
> -	.dtcm_start : {
> -		__dtcm_start = .;
> -	}
> -
> -	/* TODO: add remainder of ITCM as well, that can be used for data! */
> -	.data_dtcm DTCM_OFFSET : AT(__dtcm_start)
> -	{
> -		. = ALIGN(4);
> -		__sdtcm_data = .;
> -		*(.tcm.data)
> -		. = ALIGN(4);
> -		__edtcm_data = .;
> -	}
> -
> -	/* Reset the dot pointer or the linker gets confused */
> -	. = ADDR(.dtcm_start) + SIZEOF(.data_dtcm);
> -
> -	/* End marker for freeing TCM copy in linked object */
> -	.tcm_end : AT(ADDR(.dtcm_start) + SIZEOF(.data_dtcm)){
> -		. = ALIGN(PAGE_SIZE);
> -		__tcm_end = .;
> -	}
> -#endif
> -
>  	BSS_SECTION(0, 0, 0)
>  	_end = .;
>  
>